PINNED - AGM & GEL battery info lead battery info

[Burgerman]

NO.

NO.

NO!!!

NEVER EVER exhaust them. It DESTROYS them.

ALWAYS keep charged as much as possible, as often as possible.

Charge Every Day (overnight), if you used it at all, no matter how little.

Charge once every 2 weeks even if you NEVER use it at all.

Never discharge it more than needed. Charge several times a day if you want!

Charge a lot, often, at any opportunity while you eat or check email, and always FULLY overnight.

[LROBBINS]

If what you are thinking is that you have to exhaust the (lead-based of any type) batteries before re-charging - NO! NO! NO! NO! NO! All that does is sell batteries because it KILLS them. Charge as often as possible even if you've hardly used it at all. Ciao, Lenny

P.S. One example. Years ago a parent told me of getting that advice from a dealer - she wondered why the battery wouldn't hold a charge after only two months of this abuse. DON'T DO THAT.

[LROBBINS]

John (Burgerman) and I were writing at the same time, but you can see from our almost identical messages just how seriously we take this. Ciao, Lenny

[Burgerman]

Heard a salesman telling this "run it till its dead before charging".
And, "it will develop a memory if you don't run it right down", bullshit yet again in response to: "my scooter has no range" in a mobility shop in the town centre a week ago.

The guy was saying this because he was told this was correct by their own TECH guy in the back!

Seriously this myth stems from the so called Ni-Cad battery memory effect. And even THIS is also a myth, One that grows and grows. There are people claiming its to do with crystal sizes etc. Its all crap! It originally happened when a bunch of cells were cycled in orbit on a satellite without getting a full charge by NASA. And was widely reported. So the cells get out of balance, reducing overall PACK capacity, until a FULL LONG SLOW recharge dragged up the low cells. Or by decreased capacity from overcharge.

The Ni-Cad "memory" effect is largely a myth blown far out of proportion. The original source of the battery discharge retention cycle was discovered in early satellites which were charged with solar power. Early in orbit, the batteries were discharged at a constant rate, then recharged for a relatively specific period of time. As the cells were discharged from their original 1.6V output down to about 15% capacity, they were charged for exactly the same amount of time each orbit due to the period of time the solar panels hit the solar blanket of light.

It NEVER was real, it never related to lead batteries anyway...

http://www.repairfaq.org/ELE/F_NiCd_Battery.html This guy says it "is" but then explains that its not real anyway!

[bgmen]

is there a charger that is wheelchair and loaded to 14v?

[Burgerman]

I honestly don't know how to reply.

Try some different translation software?

If you have GEL batteries, you need to charge them at 14.10V at room temperature, and until you see 100C to 400C. Or for about 10 hours+ ideally.
If you have AGM batteries you need to charge them at 14.40V at room temperature, and same as above...

But of course you need to DOUBLE this in a wheelchair. So GEL 28.20V and AGM 28.80V.

[bgmen]

I have gel batteries must be charged to 14.1 charger of my wheelchair charge to 13

[Burgerman]

No it doesn't.

It charges AT 14.1 GEL or 14.4 volts AGM.

AFTER charge ENDS it drops to 13.5v while on and still connected.
And if you disconnect charger, battery voltage drops to about 13v.

[bgmen]

charger stops charging at 13.

[Burgerman]

You monitor this on each separate battery? Because it should charge to 28.2v or 28.6v. AS it charges?

If not then its either already charged. And goes straight to 13.5v or 27v. Or its failty and you should get a properly working charger.

[maker102]

Perfect timing for this topic. I am in need of replacing a set of Group 24 batteries however when I did a search for pc1500 batteries I came up with this on Amazon:
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=PC1500%20Odyssey%20battery
Kind of dense here, but which one is correct?

[Blade Runner]

I think the T is top terminal and thr DT is dual terminal, both top and side.
Top is what you need.

Bob

[Burgerman]

http://www.batterymegastore.co.uk/produ ... wgody0oA_Q

This is top only. And as cheap as you will get. It doesn't matter if you get dual, single, marine or whatever they are all basically the same. Any that is cheap will work.

[ex-Gooserider]

http://www.batterymegastore.co.uk/product/34-PC1500/?ref=bmuk&gclid=CN2f9PnWsb4CFYLnwgody0oA_Q

This is top only. And as cheap as you will get. It doesn't matter if you get dual, single, marine or whatever they are all basically the same. Any that is cheap will work.

Given that Maker102 is in IL, USA, I doubt that a UK vendor would be a good source but otherwise good info...

IIRC what has been said elsewhere, top or top and side terminal configurations will work for most chairs. Side terminal only can be problematic because room is needed for the connections. Also be sure that if side terminals are present, that the battery box is either made from non-conductive material, or that the terminals are totally protected from contacting the box or each other!

It is slightly easier to connect to tab or screw terminals (often labeled "marine"), but since it is easy and cheap to get the adapters to convert automotive post terminals to screw types, I wouldn't spend much extra to get marine terminals...

Given that batteries are heavy, make sure when price shopping to look at prices with both shipping and any sales tax included...

ex-Gooserider

[paulgato]

Hi, I have just bought an Odyssey battery and the manual says I MUST use a charger of AT LEAST 0.4C, or 40% of the 10-hour Ah rating, which for the PC1220, with its 10-hour rated capacity of 65Ah means a minimum 26A charger. I phoned Enersys tech. support and got conflicting stories on whether this is really necessary or not. The manual also says 14.7v is the best charge voltage to aim for, whereas BOTH Enersys tech support guys I spoke to said 14.4v would probably be better.

I am thoroughtly confused. Just to recap...

1. Manual says MUST use charger of AT LEAST 0.4C (minimum of 26A in my case) and a bulk charge voltage of 14.4v - 15.0v, with 14,7v being optimum.

2. Tech Support guy A says, "Yes, 0.4C minimum - no one knows why, but it seems it's needed in order to get stated number of cycles. 14.4v is better than 14.7v though."

3. Tech Support guy B says, "No, 0.4C is not required, but a FULL 100% charge IS required, so with a 10A charger (like the one I've already got) that's 11 hours for a fully discharged PC1220 to take it to 95% charged, PLUS another 6-8 hours on float to bring it to 100% charged. That's easier to achieve with a faster charger but a faster charger is not required. 14.4v is better than 14.7v."

4. The top expert at Sterling Chargers says, "0.4C is 'rubbish'. (That's not the actual word he used.) You CAN charge that fast but it will shorten the life of any sealed lead-acid battery, regardless of its particular mode of construction, as you will lose water and sealed batteries can't be topped up. For sealed batteries the slower the charger the better. 0.1C is about optimum. And 14.7v is too high. You need to aim for 14.4v."

So, some say you MUST use a high charge rate, some say you SHOULD ideally but it's not necessary, and some say you SHOULD NOT. And everyone EXCEPT the writers of the manual says 14.4v is better than 14.7v. I am thoroughly confused.

I wonder, with your experience of using and charging Odyssey batteries on a daily basis, what would you say is the best way to charge them, and can you shed any light on why there should be this confusion?

[Burgerman]

1. Manual says MUST use charger of AT LEAST 0.4C (minimum of 26A in my case) and a bulk charge voltage of 14.4v - 15.0v, with 14,7v being optimum.

Yes, 14.4v to 14.7v preferred.
The reason they say you need a big powerful charger is simply because it typically takes a VERY long time to fully recharge a lead based battery. Most mobility chargers are about 7 amps. Most chargers also stop charging way before the battery is truly full.

That means that if a 70Ah battery was charged at 7 amps for a whole 10 hours, it still wouldn't be fully recharged. As some is lost due to heat and internal charging (recombination) losses. And the charger typically charges at full power for only about half of that time then gradually slows down more and more towards the end.

You can rush the first part (big high Amp charger) but the last part takes about 5 hours whatever you do. The reason this is a problem is because your charger will say "ready" long before the battery is REALLY fully charged. If it isn't FULL to 100 percent it gradually sulfates over time and then it goes in the bin. This doesn't only apply to Odyssey batteries but to ALL lead based batteries.

2. Tech Support guy A says, "Yes, 0.4C minimum - no one knows why, but it seems it's needed in order to get stated number of cycles. 14.4v is better than 14.7v though."

He's not a tech guy then. He's an idiot. The reason is the one I gave above and the 14.7v at room temp helps it charge faster, and balance the cells up quickly, while not producing enough hydrogen and oxygen that they cannot be recombined into water. It aids faster charging and doesn't lose electrolyte. If you have enough time, you can charge at 14.4v to 1000thC and get the same number of cycles at only 1 amp! But at 7 amps (typical mobility charger) it takes more than overnight.

3. Tech Support guy B says, "No, 0.4C is not required, but a FULL 100% charge IS required, so with a 10A charger (like the one I've already got) that's 11 hours for a fully discharged PC1220 to take it to 95% charged, PLUS another 6-8 hours on float to bring it to 100% charged. That's easier to achieve with a faster charger but a faster charger is not required. 14.4v is better than 14.7v."

That's the first time I saw a tech guy get it correct. And exactly what I said above.

4. The top expert at Sterling Chargers says, "0.4C is 'rubbish'. (That's not the actual word he used.) You CAN charge that fast but it will shorten the life of any sealed lead-acid battery, regardless of its particular mode of construction, as you will lose water and sealed batteries can't be topped up. For sealed batteries the slower the charger the better. 0.1C is about optimum. And 14.7v is too high. You need to aim for 14.4v."

It doesn't shorten life. It extends it simply because it allows you to get a more complete charge in the shortest overnight period. It gets the BULK phase over faster, leaving more time for the CV stage and float to complete. If you charge slower, and wait long enough, same thing...

And the higher the voltage the more the battery tries to produce gas. Pure lead batteries start to do this at above 14.7v at room temperature, but they are recombinant. This means they turn the gases back into water. Up to point. All carefully tested. Stay below 14.7v and you will not lose any electrolyte. That's the reason they say charge at 14.7... Ideally. 14.4v works too, will add around 15 percent to charge time.


So, some say you MUST use a high charge rate, some say you SHOULD ideally but it's not necessary, and some say you SHOULD NOT. And everyone EXCEPT the writers of the manual says 14.4v is better than 14.7v. I am thoroughly confused.

I wonder, with your experience of using and charging Odyssey batteries on a daily basis, what would you say is the best way to charge them, and can you shed any light on why there should be this confusion?

No confusion at all. I used to sell these, and know a lot about batteries generally, charging, and advised manufacturers on such stuff. The only misunderstanding is that nobody listens!

When you DISCHARGE a battery the acid turns to lead Sulfate. And lead dioxide. And coats the plates. When you recharge COMPLETELY, this is returned to the acid. If you don't it turns to hard large crystals over time, that can never be returned to acid no matter what. And your battery is toast.

For what its worth I charge mine at up to 100Amps as I drive, and at 44A (from my maxed out bench power supply) at 14.7v (29.4 actually) as I type sat here! And all night long at 20A and 14.7v in parallel.

[Burgerman]

Simple Odyssey charge info. At 20 Centigrade.

Charge with a 3 stage charger.
STAGE 1 - CC stage ANY current, no limit, up to the 14.4v to 14.7v point. This may be hundreds of Amps, or 1A if that's all you have available. No damage will occur, its just faster or slower. Odyssey have extremely low internal resistance and so will barely get warm at ANY charge rate. Nor will they lose any electrolyte. You only get electrolyte loss if overcharged. If you never exceed 14.7 this cannot happen. The more Amps your charger the shorter this stage lasts.

STAGE 2 - CV STAGE, is where 14.7v has been reached at the max charger amps, and it now naturally falls, away gradually while holding battery at exactly 14.4V to 14.7V. Eventually this will fall to a very low level. You can continue this until 1000thC point is reached and just stop at which point its truly 100% full (fastest method), or you can do what most chargers do, and stop at 100thC (And they all say DONE, but its really not) and then go to float at a lower voltage (below).

STAGE 3 - FLOAT STAGE. For CYCLIC use float at fixed 13.5 to 13.8V, as this completes the charge in about 4 to 6 hours on a healthy battery. Current is very low at this point. You have most likely started using the powerchair after the green "charged" light came on at the end of the STAGE 2 above... So many batteries do not get completely charged. For LONG TERM storage float, use 13.3v to 13.4V Indefinitely.

[paulgato]

Aha! That's really useful information. (Just seen your second post too.) So Tech Guy B at Enersys was right then. That's good news.

Tech Guy B said that from a charging point of view the Odyssey batteries are identical to the industrial/telecom SBS battery range, on which the Odyssey batteries are based, and for which the Thin Plate Pure Lead technology was originally developed. I had discovered that the tech literature for the SBS batteries gives a minimum recommended charge rate of 0.1C, whereas the tech literature for the Odyssey Extreme batteries gives a minimum of 0.4C. Tech Guy B said the reason for the difference is that they reckon that managers of large battery banks in industrial settings are more knowledgeable, and more able to closely monitor and control the charging regime, whereas ordinary public people using them in devices where they are discharged and recharged daily usually don't appreciate the length of time it takes to get to a 100% charge, nor do they recognise the absolute importance of achieving that 100% charge.

I'm sure to you this is obvious, and now it all makes sense to me too, but to a non-expert like myself, who was getting different stories from supposed experts who were all equally sure of their opinions and who sounded equally plausible as far as I could tell, it has been very confusing, to the point where I was regretting ever getting involved with Odyssey batteries.

I think what I will do is use the CTEK 10A charger for the time being and make sure it is on charge whenever it is not being used, and then try to get hold of a decent charger of 20A-30A rating, which also has a 14.7v setting, once I have worked out where I'm going to put it. The CTEK MXS10 charger I already have has a 14.7v setting, but the CTEK 25A chargers (MXS25 and M300) only have a 14.4v setting, which is why I was looking at the Sterling Power PCU ones, which have a user-adjustable setting as well as loads of factory settings.

I should perhaps say what I'm using this battery for, as I'm not using it in a power chair. It's a project to try to get an average of 100mpg out of the Mk4 VW Golf TDi estate car I use for work. (It's a bet I have with a friend who recently bought a Prius Hybrid. So far I'm at about 82mpg overall average.) Right now I'm engaged in sorting out a permanent system for doing away with the alternator, or rather, only switching it on for very long journies where I can't plug the car in to recharge. I've already killed one cheap AGM 'leisure' battery in about 6 months of alternator-less driving, so I wanted to get the best deep-cycle-capable battery that would fit in the Golf engine bay without modification, and that, I was told, would be the Odyssey PC1220.

(I apologise if this is 'off-topic', but hopefully the parts about Odyssey battery charging will apply equally to power chairs.)

I also have a second battery which feeds power into the main car electrical system via a DC/DC step-up converter, which outputs 12A at a steady 14.0v. 12A covers daytime driving current requirements easily, but at night, or with wipers going, power is drawn from the main starter battery as well. (I can add a second 12A DC/DC converter in parallel if it seems necessary.) Currently I'm just using an old but decent car battery as the 'donor' battery, but once I've done all the taking-the-carpets-up-and-running-wiring and so on, I'll be using either one or two Yuasa YPC100-12 105Ah AGM deep cycle batteries, which will be mounted in the spare wheel well below the load area. One YPC100-12 is already installed there but not wired up yet. I was a bit concerned about the added weight of a second YPC100-12 but I'm leaning now to the view that a nicely comfortable over-supply of lead in the rear will result in a much better and more long-lived system, as then my daily short journies will barely make a dent in that 210Ah bank and the batteries will only be drawn down low on those very occasional longer journies.

I came across your site here, saw that you had been using Odyssey batteries for your daily personal transport, and realised that power chair users probably make roughly the same demands on batteries as I do by driving without an alternator, ...or probably even more. Oh. and yes, I am saving about 10% on fuel by not using an alternator. That's 10% of about £1500/year, so not negligible, although I don't expect to actually save any money with this project! I plug the car in to the mains via a discrete bumper plug whenever the car is on the driveway. I also have an engine pre-heater fed via the same bumper plug, which I switch on with a remote control key fob thing from inside the house an hour before driving off. That also saves about 5% on fuel overall, but more on shorter journies of course.

The reason I was reluctant to get a larger charger than the CTEK 10A one I already have installed in the engine bay is that larger chargers are too bulky to fit there, and/or they have cooling fans so are not waterproof. I would have had to put a larger charger inside the cabin somewhere, drill yet more holes through the firewall for the charger output cables, plus it's hard to find places where larger chargers would fit and get adequate ventilation. I found ONE place in the rear where a 25A CTEK charger for the rear batteries will fit, but nowhere in the front really. So it's good news that I don't absolutely NEED a high current charger for the starter battery and I really appreciate your advice.

[Burgerman]

I presume you have seen the F1 cars this year?

Why not keep the large amp alternator, and use an SSR to disconnect it during engine power, and reconnect it when you need to brake vie a link to the brake light switch. That will take a load of the brakes, take no engine power at all and charge your battery...

And in inertial switch can be used too or instead so that the alternator adds power on overrun or while engine braking.

[paulgato]

Good thinking Burgerman. If I could do what you suggest, I would. In fact on my list of things to do today is to fit the replacement alternator that has been sitting in a box in my living room the past couple of weeks. I managed to destroy my current alternator by experimenting with regenerative braking. The problem is I don't know enough about alternators.

I successfully disabled the alternator some months ago by disconnecting the wire that goes via the ignition switch and via the dash warning light to the alternator. With that disconnected the alternator won't start up. Switching the alternator back on is easy - just reconnect that wire. However, once that wire has been connected and the engine started, disconnecting it won't stop the alternator as it provides its own field current once it is running. So the difficulty is in switching OFF the alternator once it is running.

I destroyed the alternator by doing the following. I was wanting to fit an ON/OFF switch on the dash for the alternator, but also wanting to be able to connect that switch in with the brake lights, so as to achieve a degree of regenerative braking. (an inertia switch would be better) I had read somewhere that if you softly ground the field current (through a resistor or a light bulb) then that will stop the alternator producing current. I tried that - or thought I was trying that - by grounding the 'IGnition' wire I had disconnected - grounding the end of the wire still attached to the alternator. I tried first with a 5w bulb. Sure enough, the battery voltage slowly dropped from 14.4 volts down to about 13v, but as soon as I disconnected the bulb, it went back up to 14.4v. I then tried a larger bulb (lower resistance). The only other bulb I had was a 55w headlight bulb. That didn't light, and to be honest I don't now remember whether the voltage dropped when it was in circuit, but after I had tried that larger bulb I found the alternator was putting out 14.4v even when the IGnition wire was disconnected and the engine had been off for a while (and then re-started obviously!) I found that even with the engine off and the key out of the ignition, there was now 800mA or so getting into the alternator direct from the battery via the big fat charge wire - energising the field winding 24/7! Presumably I had blown/shorted at least one diode in the alternator. Since that little experiment I have had to disconnect ALL wires from the alternator to prevent it putting out a charge, and to prevent it draining the battery when parked up. (Not raining (much) and no work on, so I should get off the computer and fit that new alternator today.)

So yes, if there is another way to switch the alternator on AND OFF with the engine running, then I am all ears. I had considered a complicated circuit involving a step-up voltage booster, to fool the alternator into thinking the battery voltage was a couple of volts higher than it actually is, but after that little mishap I kind of lost confidence and put the idea on the back burner. How would this Solid State Relay idea work then?

(I am aware this really IS going off-topic now!)

(Someone once suggested putting a couple of NiCad cells inline with the alternator's battery sense wire to up the sensed voltage a couple of volts and stop the alternator putting out, hmmm... Or if I could fit an alternator from the newer Bluemotion Golfs which use renenerative braking, and control that somehow...? Or somehow fit a an electro-mechanical clutch so the alternanator doesn't even spin when it's not needed...?)

[Burgerman]

http://www.metrompg.com/posts/alternator-optional.htm

Interesting...

Seems to me that all you need do is use a switch, brake switch, inertia switch, link to fuel injection to detect low injector pulsewidth etc to activate alternator at any time you are decelerating.

LEAVE ignition light wire alone...
Connect alternator to battery via heavy wire wound resistor with a value that only allows say 2 amps max to flow if battery is 11.2v (dead) when charging. The alternator tries to put out 14.4 to 14.5v regulated usually. This means it will only charge at a negligible 1 amp (ish) normally through the resistor. That will use negligible power and it will have almost no EMF or fuel cost. And wont hurt it. (I think...) Or you may need a small bulb from alternator output to ignition light connection? Research...

When braking etc, bypass the resistor with a solid link via a DC to DC solid state relay. So it charges at whatever amps it takes to pull the battery up to 14.4v.

And 45psi in the tyres, 0-20 oil, lower car, oil rather than grease in wheel bearings and CV joints, tape over all joints, and add some two stroke oil to the fuel tank. That gives smoother more complete combustion, and makes it run better too.

And only go downhill...

[paulgato]

Well, I did get the 'new' (used) alternator installed yesterday just before the rain started.

Thanks for the link. That guy also posts on http://www.ecomodder.com, which I find to be a good resource. I have a thread there where I've been documenting this particular project.. It's long and rambling but there is some good solid data there too, such as the current consumption of every piece of equipment in the car...

http://ecomodder.com/forum/showthread.p ... 27179.html

Seems to me that all you need do is use a switch, brake switch, inertia switch, link to fuel injection to detect low injector pulsewidth etc to activate alternator at any time you are decelerating.

I might try some of those things but first I need a way to stop and start the alternator while driving.

LEAVE ignition light wire alone...
Connect alternator to battery via heavy wire wound resistor with a value that only allows say 2 amps max to flow if battery is 11.2v (dead) when charging. /.../ When braking etc, bypass the resistor with a solid link via a DC to DC solid state relay.

This is interesting. I hadn't considered interrupting the main charge wire, but if it were connected with a permanent resistor in series which is bridged out on demand there'd be no risk of voltage spikes I guess. In fact my original idea was to use a deep cycle battery and a DC/DC converter set to output say 20A at 14.7v. The alternator would then 'see' that 14.7v on its battery +ve reference or sense wire and would conclude that its services were not required. And if the current demand was greater than the 20A the voltage would drop and the alternator would make up the difference. I liked that idea precisely because I wouldn't have had to change the car's electrical system in any way (and wouldn't risk breaking any alternators - ha ha.) I didn't find a suitable voltage-adjustable converter though, so went with interrupting the field exciter wire instead. I'm still thinking that using the sense wire would work, as that is what the alternator already uses to adjust its output from 0A to 90A. In theory I'd just need to switch that sense wire between its existing connection point and a voltage source which I can control, and which will be high enough that it will stop the alternator from charging. Depending on how much current is drawn by the regulator via that 'sense' wire, the new source could be as simple as a NiCad battery pack, or could be a small, low current DC/DC step-up converter.

And 45psi in the tyres, 0-20 oil, lower car, oil rather than grease in wheel bearings and CV joints, tape over all joints, and add some two stroke oil to the fuel tank. That gives smoother more complete combustion, and makes it run better too.

51psi in the (LRR) tyres for the past year with no issues. (Corners much better with harder tyres too.) I changed the gear oil and put some Molyslip in - that was dead easy, cheap and made an immediate, obvious reduction in rolling resistance. Oil in bearings/CV joint? Won't it fall out/wash out? I've heard of folks using synthetic grease in wheel bearings. Two stroke oil in fuel...? Really? That makes me a bit nervous - those 30,000 psi injection pumps are expensive and sensitive.

All good suggestions but I've become a bit bogged down with this 'alternator delete' project so I feel I have to focus first on getting the basic battery charge/discharge system up and running and properly installed/safe/reliable/neat before getting too involved with other things. I've had good mpg gains from plugging the car into the mains every night, but it's been taking huge amounts of time, and I'm looking forward to finishing it.

[Burgerman]

51psi in the (LRR) tyres for the past year with no issues. (Corners much better with harder tyres too.) I changed the gear oil and put some Molyslip in - that was dead easy, cheap and made an immediate, obvious reduction in rolling resistance. Oil in bearings/CV joint? Won't it fall out/wash out? I've heard of folks using synthetic grease in wheel bearings. Two stroke oil in fuel...? Really? That makes me a bit nervous - those 30,000 psi injection pumps are expensive and sensitive.

Moly slip is snake oil.

So is PTFE, and all the other additives.

I built automotive rolling road dynamometers, nitrous injection systems, and race engines for drag bikes and cars for many years.

Oil in bearings is kept there by seals. cant leak or wash out, same with CV joints. Two stroke oil at around 200 to one will make your engine both quieter and get rid of the clatter when cold and run more efficiently. Wont hurt anything. Premix it with a gallon of fuel, and tip it in...

[paulgato]

We will have to disagree about Molyslip Mr Burgerman. I've used it for 30 years in both gearboxes and engines. I don't use it in my present engine though. I use the 'Longlife' oil that the VW dealer tries to charge £44 a can for (!) but I'm sure it helped in the gearbox. I suspect that engine oils have improved a lot and now Molyslip doesn't help much. I tried it in this engine once but couldn't detect any improvement.

In my lazy youth I used to sometimes add half a can of Molyslip to an engine that was overdue for an oil change, and you could hear (and feel) a very obvious difference: it sounded like the oil had been changed when all I'd done was pour 150ml of grey gunk in. (Quieter, more free-revving.) Engines would also run measurably cooler with Molyslip. I agree about Slick 50 though (PTFE). I tried that in a petrol engine once, many years ago. It did work, but it only had an effect until the oil was next changed, nothing like the "50,000 mile protection" they claimed, plus it was expensive, so I went back to using Molyslip.

I read up on putting two-stroke oil in the diesel tank. It seems many people swear by it. I might give it a go at some point, but I'll do some more research first, just to be on the safe side. Do you use that yourself?

One thing that has a very marked effect in this car is using premium diesel. I use Shell Ultimate diesel. More expensive, but for my car at least it pays for itself in increased mpg. From memory the mpg boost was about 7% and the extra cost was 6%, so only a marginal COST benefit, but it also made the engine run much more smoothly. (Perhaps they put two-stroke oil in it - ha ha.)

[Burgerman]

When working for bike magazines (performance bikes) I tested every oil additive and many oils to find out for sure. Several bikes, and under controlled conditions using my own inertial chassis computerised dynamometer. Controlled air, engine, oil temperatures, corrected for pressure, temperature and humidity.

No additive had any affect on any power curve at all. Only changing oil grade had any affect. And that was under 1 percent overall. Wynns, STP, Molyslip, Slick 50, etc etc. All a waste of money.

Molyslip is just Molebnium Disulfide in a cheap base oil. Its a friction additive. And decent oil already contains a package of friction modifiers and detergents, high pressure long chain molecules for high film strength etc.

Adding stuff to it can make the oil worse. For e.g., too much Zinc (another additive) causes cams to get pitted. Too much moly or other friction modifier causes roller or ball bearing races to slide instead of rolling. That causes flat spots, and subsequent failure. Same with roller cam followers etc.

Do yourself a favour, use a quality modern thin synthetic like 10w20 mobil synthetic and don't mess with its carefully engineered balanced package.

[paulgato]

Interesting. Perhaps we don't disagree that much. I do think it is pointless to add anything to the good quality synthetic oil I am currently using, but it most certainly improved the old mineral oil I was using in engines years ago.

I say "I changed" the gear oil a year or so ago and noticed that very dramatic improvement in rolling resistance, but in fact I got my local mechanic to do it. It took him ten minutes on the ramp but would have taken me a couple of hours grubbing about under the car on a muddy driveway. I got him to put the new oil and the Molyslip in at the same time of course, so it was not a scientific test. The improvement could, I suppose, have been entirely due to having new oil in there, although VW don't specify any replacement interval for the gear oil. They claim that it can be left in there forever. (They're probably lying, to make it look like their cars need less maintenance than they actually do, but that's what they say.) I used the latest version of the recommended VW gear oil.

So it may be that my opinion on Molyslip is out of date, or it may be that every time I added Molyslip to existing oil in gearboxes and noticed an improvement - both in rolling and in shifting - it was because the existing gear oil was old and tired, and the addition of Molyslip compensated for that.

[Burgerman]

The improvement could, I suppose, have been entirely due to having new oil in there, although VW don't specify any replacement interval for the gear oil. They claim that it can be left in there forever. (They're probably lying, to make it look like their cars need less maintenance than they actually do, but that's what they say.) I used the latest version of the recommended VW gear oil.

The problem is that unless you can do your back to back tests in scientifically controlled conditions, with an accurate digital dynamometer to plot rear wheel BHP in a controlled test cell, as I did, then you cant really know. Measuring MPG on the streets, and subjective feelings, do not give accurate results. People that have just had a car valeted, or serviced will tell you it runs better and is quieter, does more to the gallon. When its simply not true. They FEEL that this is the case, the Dyno says not...

Testimonials are pretty meaningless, and the placebo effect of adding something you expect to do some good all makes it seem real enough.

You change engine oil because the corrosion inhibitors, and detergents get used up, and because it gets loaded up with carbon. There's no corrosion inhibitor or detergents in gear oils. And no carbon getting past the pistons. And no acids from combustion. And so no need to ever change gear oil. Its true that some steel from bearings and gear teeth (wear) would contaminate the oil over very high mileages, but they fit magnetic traps to grab that and hold it in one spot. After extreme mileages around 10x that of the life of the vehicle, there may be some measurable viscosity change too, but its so small as to be not worth worrying about. And its in the direction of lowering viscosity as long chains get cut up. Hence most manufacturers quote top up or check intervals but no oil change for the life of the vehicle.

[paulgato]

I'm certainly not doubting the results of your scientific tests with the dynometer (?) and as I say I'm not sure whether the improvement after the gear oil change was due to changing the oil for fresh oil or the addition of Molyslip, but the effect was not just subjective and was very dramatic. Or maybe the newer version of VW gear oil is much better than that installed ten years earlier when the car was built?

I actually didn't think changing the gear oil would have much of an effect; it was just that it was so cheap and easy to do I thought I might as well eliminate that possible source of friction. I remember driving away from the garage and being amazed at how much further the car would roll in neutral down familiar stretches of local road. I then took it on a local 'test route' where I measure the effect on mpg of various changes. That route is a straight stretch of dual carriageway of about 5 miles, where cars can safely overtake me, and where I can set the cruise control to 50mph and set the car's mpg trip meter at a certain point and note the mpg average at another point at the end of the circuit. It's a two-way test run, incorporating a roundabout at the half-way point. The roundabout is not taken at 50mph (!) so there is some possible variation in driving efficiency at that point, but after the gear oil change I got my highest ever reading, beating my previous best reading by about 4 mpg. (about 5%) I know there can be many reasons for variations in mpg, including atmospheric variations, but it was a very still morning, and the fact that it was my best ever reading by a margin tells me it wasn't just favourable weather.

I try to test all the changes I make. Obviously some of my judegments are subjective, but some are a bit more measured. When I first started monitoring my overall average mpg closely the car was getting (as shown on the dash) about 55mpg. A year later (same approx ambient temperature) it was showing 83mpg. Now it's showing about 93mpg, and I expect it to improve as the weather warms up over the summer. (The dash mpg meter is optimistic by about 7%.)

Once the alternator-delete project is done and dusted and stabilised, I have a few things on my list to try next. I'll add to that list the wheel bearing lubricant change, and possibly this two-stroke oil thing. Also a full underbody fairing, and stripping a bit of unnecessary weight such as the A/C system, roof rails, and anything else that has no function but which won't make the car look too weird when removed. I'd like to try another engine re-map. The first one I think made the car more efficient in an absolute sense but made it much more difficult to drive slowly and frugally in the real world, so I had it put back to standard.

[Burgerman]

You cant measure fuel economy to 5 percent like that. Far too many environmental and vehicle variables.

I have done this oil thing on diesels many times. Humour me. Go buy some cheap (cheaper the better) 2 stroke oil, or even engine oil. Mix enough oil/fuel in a can to get an approx. 100 to 200 to 1 mix in your tank. Not remotely critical. Tip it in and top up tank to mix it.

Then tell me its not quieter and smoother, especially from cold. And gains MPG and theres zero smoke. Its not just subjective like a quick MPG test is, its measurable on a Dynamometer. Ask me how I know!

I used to design and build computerised pure digital automotive chassis dynamometers for a living in the 80s, which I got into because all the commercial ones were not accurate enough to do any seriously accurate back to back testing on the drag bike and car motors I was building for customers...
I build my own fuel injection, turbo, and nitrous injection systems too. Serious stuff that gets around 550 BHP per litre from a bike engine.

Build yourself a nitrous injection system for your car cheaply!
http://www.nitrous.info one of my 20 year old sites...

[paulgato]

You're clearly the man to ask about these things Bugerman, and I will try the two-stroke thing once I have done my own 'due diligence' on the subject, and once the alternator delete thing is done. (Though maybe not the NO2 thing right now! Interesting to read though.) I will remember to let you know the results. I try to only make one change at a time so I have a better chance of testing whether it works or not - preferably over at least one full tank of fuel.

The testing thing is difficult. Dyno testing is not posssible for the vast majority of us. The accepted standard out here 'on the streets' is to do A-B-A testing, where you test, make the change, test, change back to standard, test again. For some things that's possible; for some it's not. The testing I did to determine the projected effect of driving without using the alternator was possible to do in that way; use of fuel additives is not so easy, as you can't take the additive out of the tank once it's in there. (Then the best you can do is an AAA-BBB test.) Tests like this should be done on a calm day and in quick succession after thoroughly heat-soaking the engine. (I often do test runs on familiar local roads after coming back from a long journey, before going home, when I know the engine, drivetrain and tyres are all nicely warmed up and are not going to warm up any further. It generally takes about two hours driving before the mpg will hit its peak.) The weather can make a huge difference (temperature, humidity, water on road surface, air pressure, wind speed) and we all try to take account of that, more or less successfully.

There are judgement calls at every step. Some will be wrong, some will be right. The fact that my overall displayed mpg has gone up over the past 20 months from 55mpg to 93mpg tells me that most of those judgement calls, based on the flawed testing I've been doing, have been right. Sometimes you just KNOW something has got better because its blindingly obvious. The gear oil change was one of those "Oh my god, I didn't think it was going to be THIS much better!" moments, as was getting the front wheel alignment adjusted to zero toe-in, ...and as was my first alternator replacement 18 months ago, which incidentally fixed a rough idling issue that turned out to be due to a frozen alternator freewheel pulley that I didn't even know existed. Suddenly I could cruise smoothly in 5th gear at 26mph at tickover and get stupendous 100+mpg around town in light traffic. And even at 30mph, the slowest I could comfortably drive before in 5th, mpg was WAY up after the alternator change.)