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Remote oil cooler on manual transmission

Remote oil cooler on manual transmission

Remote oil cooler on manual transmission

I have a small car (a Liege) which uses an 850 cc engine and a small 4 speed gearbox, the latter "not being known for its reliability". At Mallory Park racetrack during an endurance event the oil badly overheated and the gearchange became more tricky. The car eventually suffered a bad gear downchange (not me driving) which broke some teeth off the layshaft. To give you some idea of the pressure we put our little cars under, our team came 5th out of 26 teams involved and we beat a team driving a pair of 6 litre, 500 bhp cars; one a Cobra Replica and the other a Lola T70 replica.

I now wish to fit a small oil cooler to the gearbox using an electric pump. I have sourced the cooler and gear driven pump. I intend to use a thermostatic switch to control the pump.

Has anyone here relevant experience of this type of project and what are the pitfalls, if any?

I've found very scant information on the web and I've tried the search facility here with no success.

Thanks in advance for any advice, as long as it's not "use a better gearbox" because I'm hoping to keep the car original.

Paul W.

RE: Remote oil cooler on manual transmission

The oil is already thrashing around in there pretty well, so a finned sump/ sidecover/ whatever might be sufficiently effective.

If you're going to bother with a pump, it makes sense to also install a filter to catch pieces of the gearbox before they can cause a cascading failure.


Mike Halloran
Pembroke Pines, FL, USA

RE: Remote oil cooler on manual transmission

I've heard this many times on hydraulic systems - but it doesn't work. If you do the calculations there is not enough heat rejection from metallic piping unless you are borderline. And consider that the air washing over the tranny is pre-heated by the radiator, engine and exhaust system.

I would strongly suggest adding the pump/cooler and using a good full synthetic oil. And as far as advice, the NASCAR teams all use differential oil coolers. Just Google "differential cooler" and you will get lots of hits.


RE: Remote oil cooler on manual transmission

you state that the oil overheated badly - do you have any idea of the bulk oil temperature in the gearbox?

as long as the temperature does not get above 160 degree C the temperature should not be a problem, but the viscosity might well be - bear in mind that too high a viscosity promotes excessive temperatures and possibly foaming and too low viscosity excessive wear and catastrophic failure. you therefore should find out first what causes the problem.

what type of oil do you use in the gearbox?

one final remark: use steel piping and not copper: copper acts as a catalyst that promotes oxidation of the oil and subsequent thickening, deposits etc.

RE: Remote oil cooler on manual transmission

I cannot address your problems from here, but I can tell you some of the "cures" we attempted in out Lotus gearbox for endurance racing, specifically the "Seis Horas de la Ciudad de Mexico" in 1973.  First we did the 'dry sump' to a small reservoir and heat exchanger (an OEM MGB oil cooler). The oil still heated up significantly after only a few minutes.  I still think the idea is sound, looking back.  I think we were using the wrong lube.  Anyway, we survived then, but eventually I went to using off the shelf ATF in the early 80's and have had no problems since.  My son still has the car and it is still using ATF...recently spent 6+ hours at Willow springs testing and no problems.  The electric pump and all the Mickey Mouse plumbing was a waste of time as I see it now. I have not checked the trans temp lately (mid 80's !!!)  This has given me reason to ck again as we are entered in a vintage race first weekend of April...I foresee no problems, however.

Just FYI, NASCAR still uses pumps and coolers on their final drives AND their gearboxes!


RE: Remote oil cooler on manual transmission

Gentlemen, thanks for the ideas and very prompt responses.

The gearbox and bellhousing is of a one piece cast design. There is a top cover but no sump plate is fitted so I have no scope for a heatsink. On the plus side, it is made entirely of aluminium.

I certainly agree about the need for an inlet filter. Fortunately the pump is purpose designed and does have a large diameter inlet strainer/filter to protect the bronze pump gears.

Due to the physical size of the car (it's only ten feet long, nose to tail) and a very small engine bay, I can't fit a long metal pipe to act as the heatsink - it really has to have a cooler matrix, which I've already sourced (a neat and robust cast alloy item from an ATV/quadbike). The distance from the gearbox to the available space for the cooler is only about 18 inches, which will have to include about a foot of flexible rubber. Because the car is used for off-road classic trials as well as on the track, everything has to be tucked up above chassis level for safety, unfortunately that's also out of the under-car airflow. I may need to fit a small electric fan to the matrix, this would be piggy-backed off the pump electrics.

The oil used until now has been as per the manufacturer's recommendation (EP80/90, I used a semi-synthetic). I intend to use a fully synthetic oil from now on; either Redline or Lucas or one of equal quality. I don't know what the oil temperature was after the failure as I had no facility to check it. However, on entering the paddock after the failure, the box was so hot I thought it had lost all its oil. On removal of the level plug it was obvious there was sufficient oil in there but the viscosity was more like paraffin than oil and it smelled scorched.

Despite only having a very noisy first and a good top gear working, I left the car to cool for an hour or so and managed to limp it 70 miles home.

The gearbox was originally designed for an engine which produced about 30 bhp so cooling was no issue but mine has been tuned to produce almost double that. Some owners have fitted other gearboxes but they are all larger/longer and it involves cutting out a welded crossmember of the powder coated chassis. I'm very keen to keep my car original in most respects - there will probably only ever be 60 of them and many folk think they are a future classic.

One repeat question - some time ago I asked for ideas on the use of ATF in this gearbox in place of EP oil. Obviously, ATF will flow through the pump very nicely but will it be suitable in other respects? Does it absorb and dissipate heat as well, or better than EP oils?

Thanks again for the help.

Paul W.   

RE: Remote oil cooler on manual transmission

Doubling the outside surface area (where 95% of the thermal resistance is) of the transmission would provide enough cooling.
IMO the easiest way to do this is to install fins on any flat exterior portion (even a inch long - the individual inches add up).
Make the fins of angle aluminum or copper - say one inch in contact with the transmission body and four inches (or more)out (the actual "fin" width). Make the fin of one quarter inch thick material to decrease temperature drop in the fin. Adher the fin base with high temperature adhesive or a mechanical system.

Do some numbers on the fins (calculating fin efficiency etc.) using your old heat transfer textbook.  

RE: Remote oil cooler on manual transmission

Thanks for the alternative idea but I'm committed to the separate oil cooler method; I've already purchased the parts.

Regards, PW.

RE: Remote oil cooler on manual transmission

Just adding surface area is only half the battle - you still need the air flow. And the aluminum will corrode which significantly lowers its heat transfer. (or it gets painted which has the same end effect) If it was that easy we would all be driving air cooler cars!

As for the temperature, you could measure the case temperature as it would be close to your oil temperature. The easiest way would be to use an adhesive-backed thermocouple and a relatively cheap Digital Multi Meter. (Not the only source, but one of the cheapest. http://www.omega.com/ppt/pptsc.asp?ref=SA2&Nav=tema03)

If you try to use an infrared temperature sensor make sure you measure a surface that has been painted as this will match the default calibration of most of these instruments. If you try to measure the bare aluminum surface you will need to recalibrate the instrument (and not all can be) plus you don't know what calibration factor to use. (values listed in tables are only an estimate)


RE: Remote oil cooler on manual transmission

With your extra HP output and such a small transmission I would venture to guess that the simple cooler you have in mind plus the extra oil capacity that such a system would add should do the trick.

Combine this with a good synthetic oil and all should be well.

That is, of course, if the transmission can physically withstand double the HP.

Maybe that is a factor that has been over looked up to this point.

It could be flexing shafts and overloading bearings to the point that the extra friction is creating more heat than can be deal with.

It could simply be a design flaw that can only be fixed with a stronger replacement trans.

There is also the option of several different types of treatments for gears and such (cryo-treating, coating and so on)that may help.

Food for thought

RE: Remote oil cooler on manual transmission

Bill, you bring up the point that I was hoping someone else would elaborate on...That being, is the gearbox failure caused by the overheating or is the overheating caused by the overloading/flexing/failure of the gearbox?

I have a difficult time envisioning a lubricant so overheated as to cause 'gears to fail' without some really terrible signs, e.g., lots and lots of SMOKE !


RE: Remote oil cooler on manual transmission

"I have a difficult time envisioning a lubricant so overheated as to cause 'gears to fail' without some really terrible signs, e.g., lots and lots of SMOKE !"

Rod, The gear failure was caused by a bad down gearchange, not by the high gearbox temperature (that's not what I said).

I think the reason for the bad gearchange was that the synchromesh was working unpredictably due to overheated oil. I had noticed myself that third gear in particular was beginning to snatch when changing up and down. I've noticed this before when driving hard on the road.

On this occasion we were really driving hard and car was spending a lot of time at 6,500 to 7,000 rpm in third and top. There is no doubt we were pushing it to its limits. I still think a better quality oil plus positive temperature control is the answer I'm looking for.

I've done some more research today and found a source of a solid state thermostatic switch that can be attached to the gearbox casing using silicon adhesive. These switches cost next to nothing, have a small metal body and are normally used to control temperature in cookers, coffee machines, etc. They are available in a range of "ON" temperatures, in 20 degrees C increments. I intend to try wiring one through a relay to switch the pump on/off.

What is the suggested optimum temperature to run a synthetic gearbox oil?

Thanks again for all the input, it's much appreciated.

Paul W.     

RE: Remote oil cooler on manual transmission

Bill, You have a very valid point about metal treatments such as cryo; it is something that had crossed my mind even before my gearbox broke after talking to a company rep. at a kit car show here in UK.

The reason I was interested is that another Liege owner friend has supercharged his car and now it physically breaks gearbox parts at low speeds due to the extra torque. He's told me the metal around the keyway on the first motion shaft gives way. Reliant (factory now long gone), whose gearboxes we cannibalised to build our Lieges, had a reputation for poor reliability / quality towards the end of the production run. I think substandard heat treatment by a sub-contractor was possibly one cause. Cryo might help and I might investigate further.

My supercharged friend has temporarily given up Classic Trials until he can change to another stronger gearbox type. He jokingly claimed an RAC "Triple" award from the Trials club because he went home by recovery truck three times in one year, all gearbox failures. A normal "Triple" award means no hillclimbing failures all year, on the three main trials run by the Motor Cycling Club (yes I know we have cars, it's just the way it is).

One or two owners have fitted a Suzuki Jeep box, it's one of the few we have available that can physically fit under the car. Unfortunately it's a far from straightforward conversion as it's a bit too long. As well as chassis cutting and welding, the engine has to be physically moved forward which has implications on the competition class regulations. The gearbox change has been authorised by the governing body but by moving the engine the car then becomes a "special" and has to compete against large rear engined specially designed trialling cars, which have other, big advantages over our little ones.

I really do want to avoid changing this gearboxbox. winky smile  

Paul W.

RE: Remote oil cooler on manual transmission

Obviously you have a problem...A problem related to the synchros, for sure and possibly to the type of lubrication you are using.  I do not, however, feel that it is temperature related.

Before going off half cocked, put a temp probe in the gearbox, mine was a Smiths oil temp gauge mounted through the fill plug...Just temporary, long enough to get some readings. Once I found that we were wasting our time with pumps and such,  I replaced the fill plug.  After twelve or thirteen years of fooling with the perceived problem, balky shifts, 'grinding' and persistent failure of the synchro 'clips', those evil little ten cent pieces in the Ford synchro.  I switched to ATF (recommended by a friend I trusted) in 1980.  Since then, through the 80's SCCA Regional and Nationals, I never experienced the problem again.  The gearbox (close ratio Lotus Elan/Cortina/Anglia, ex Alan Mann Works) has had NO problems since.  The car was sold in '95, re sold several times to various New England competitors.  My son bought it in 2004 and I restored it over the last several years.  The gearbox is absolutely as it was when it left my shop in 1991.  None of the various owners had even changed the oil...safety wired and sealed...I can recognize my work.

Now, if there is something amiss, something not correctly engineered/installed, etc.  I can go with that.  Sorry, I just cannot see excessive temp as a causal factor in a gearbox failure as described.

Now, I saved this for last because I may be way off base...How big is the fist that's rowing that little gear lever around?


RE: Remote oil cooler on manual transmission

Rod, you have answered the question I asked some time ago about the use of ATF in manual car gearboxes. At that time I flew Sikorsky S-76 helicopters, one of which used ATF in all three gearboxes in the transmission system and I was interested in minimising power losses caused by a high viscosity EP oil in my little car, by replacing it with ATF.

I think this may be a good way forward but have never had enough confidence to use it. I may well do so now.

Paul W.

RE: Remote oil cooler on manual transmission

Paul, I really understand.  I was told by my friend that I could use ATF several YEARS before I actually tried it.  Since then, I have used it in several trannys with 'limited' problems.  The 83 T-Coupe used ATF as OE specs, no problems, my 1939 Buick three speed, no problems (a real sweet shifting box)---1959 Metropolitan, easier shifting, a little noisier and a small leak I have not found yet (cause I have not looked all that hard?)---1930 Ford with '39 gearset, no problems, but it is noisier, not that that it matters all that much in a Model A.  I just wish there was some way I could improve the shifting in my '63 Mini Cooper race car...it can be a bitch sometimes.

A bit of a 'crap shoot', is it not?  I just 'calls 'em like I sees 'em'...Following my example may or may NOT be wise!
Best of luck.


RE: Remote oil cooler on manual transmission

I'll perhaps bite the bullet and try using ATF before I fit the cooler ans see how it works.

I can drill, tap and blank off a pipe outlet in the lower casing for the cooler before I rebuild the box. I can then easily gain access later while it's in the car. I intend to use a modified level plug for the return fitting so future access to will be straightforward.

Having just thought about this, I can drill and tap to use a second filler or drain plug as a blank, then modify it later to take the supply pipe.

Thanks again for all your replies, everyone's help is very much appreciated.

I'll report back - I may be gone some time as I have a delivery of 5 tons of top soil for a new vegetable garden to deal with as my immediate priority... so my wife has told me. We only ordered 2.5 tons so if anyone's got a  wheelbarrow they're very welcome to fetch a load or two. smile

Paul W


RE: Remote oil cooler on manual transmission

use of a ATF might be a good alternative. ATF's are very oxidation resistant and that could help you. if you want to try it, you are advised to use a topquality synthetic ATF.

You can get an idea of the types that are suitable here: http://www01apps.zf.com/kst464/ZF_InteroeleV2_download/download.asp?doStatistik=1&doMode=1&;mode=3&doID=1&id=2371

you should choose a product listed for one of the 5 or 6 speed automatics. these products differ somewhat in frictional characteristics, but all have a very high oxidation and thermal stability. getting them could be a problem since they are only used when rebuilding the transmission and for factory fill. you might try a firm that specializes in transmission rebuilding. they might be willing to sell you a few litres.

another suitable product group are the products used in aisin 6 speed automatics installed in or example volvo, peugeot and alfa romeo cars. they have similar characteristics as the ZF-advised product. obtaining them is just as difficult unfortunately.

RE: Remote oil cooler on manual transmission

Romke, thanks. The link didn't work but I think I found the correct website.

There's a very good motor factor near me and also a transmission specialist so I'm sure I can find a good quality fluid.

RE: Remote oil cooler on manual transmission

I noticed that ZF has taken part of their site down for maintenance. The link might work again next week.

RE: Remote oil cooler on manual transmission

FWIW I have done a lot of work with PSRUs (transmissions for aircraft) and I have always designed in a cooler with a return spray at the gears and bearings that are loaded.The big advantage for remote reservoir w/cooler is (as was mentioned) not having a box whirl around a lot of oil. The caveat with an on/off switch is; where does the oil in line go? Does it drain back into the box and overfill it, or is there a reservoir that can be brought back on line? Just a few thoughts as I have never designed a gear box other then dry sump.


I don't know anything but the people that do.

RE: Remote oil cooler on manual transmission

Thankyou for the idea.

I understand the advantages of a properly designed dry sump system (I'm a helicopter pilot with some engineering background) but speaking from a practical point of view I don't have the resources or time to research/experiment this avenue.

My concern would be that in an essentially "empty" dry sumped gearbox I couldn't guarantee correct oil supply to all areas needing it. I don't think it's been done before on this type of gearbox so I would definitely be out on a limb.

The use of ATF plus a cooler & circulation pump is, I regret, all I can reasonably do.

Paul W.

RE: Remote oil cooler on manual transmission

A couple of extra thoughts. I spoke to my local transmission specialist yesterday; he is changing some parts over for me.

Having discussed the issue this with him he advised me to use a top-quality 15W/40 engine oil instead of ATF because from his own experiences.

He does think that the gearbox oil cooler is a very good idea; he rebuilds transmissions for a number of local car racers and he said he is now trying to get them all to fit oil coolers. He says just use a manual switch to run it as soon as the car warms up, period. I may still fit a thermostatic switch for a couple of reasons.

The engine oil issue makes my life easier because that's what the engine uses; because of the small engine size I can change both oils at the same time and the whole lot will use up one 5 litre can winky smile .

RE: Remote oil cooler on manual transmission

Sounds like you have it all under control, Paul.  I see no reason that a good quality engine oil will not perform adequately, after all, I race a '63 Austin Cooper Mini in vintage ( 115 hp at the wheels 1380cc ) and the little close ratio four speed box works well with my Redline 50 .

Hmmm. Looking at the Mini's gearbox, I guess I already have a transmission AND differential/final remote cooler. winky smile


RE: Remote oil cooler on manual transmission

the engine oil might be an alternative. bear in mind though that the viscosity is higher then ATF and that will problably result in a higher oil temperature. that then compensates somewhat for the higher viscosity, but introduces additional frictional losses that generate heat that must be dissipated.

do you have the possibility to test both oils and do some temperature measurements?

i still prefer the ATF, most applications use an oil that is rather too viscous.

as far as wear is concerned: both types of oils contain anti-wear additives - so there you should not worry.

the best way to sort things out is to run the vehicle on a rolling road and do temperature mesurements with both types of oils under identical circumstances. that problably would show which type works best.

RE: Remote oil cooler on manual transmission

romke, in years past, we have taken 'on track' readings for all things ' hot' including the gearbox.  In the early 80's I found that the ATF was SUBSTANTIALLY cooler than the 80W-90 OR the Castrol (40 I think)engine oil.  That was one of, if not THE, determining factor in my switching the Lotus/Ford gearbox to ATF.  Yes, Mildred, I had to "prove it" to myself...ATF is what I still use today. (Raced the car last weekend, track temp was 70ish and temps were barely readable...gearbox was only 140f after 12 laps at Willow Springs.


RE: Remote oil cooler on manual transmission

Engine oil or ATF? Decisions, decisions!winky smile

Whatever it is, it will be properly cooled sooner or later.

Great thread, btw, I'm enjoying hearing all these different opinions.


RE: Remote oil cooler on manual transmission


what shifting problems do you experience in your mini and what oil do you use in the engine/gearbox/diff combo?

i remember that those gearboxes had a tendency to shift well with fresh engine oil, but shift performance deteriorated when the oil was longer in use. the most likely cause for that was the breakdown of the type of VI-improver used in the 60-ties and 70-ties and the limited detergency of those products that caused some deposits (not visible to the naked eye) on the synchromesh mating faces essentially changing the rictional characteristics.

i guess modern synthetics based engine oils with much less (and better quality) VI-improver and far better detergency may well improve on that.

in regard to shift performance it might be interesting to compare engine oils designed for 4stroke motorcycle engines. basically there are to types: MA and MB, that differ in frictional characteristics. The MA types give high static and dynamic friction when used with wet clutches, the MB type gives lower friction. although the frictional characteristics are engineered to work well with clutches, they might also influence synchromesh behaviour. the frictional characteristics are managed through the inclusion of friction modifiers in the MA types, the MB types do not include a friction modifier.

apart from being "MA" or "MB" the oils further meet the standard automotive engine specs and are available both in synthetic, partly synthetic and mineral types.

you therefore could experiment with synthetic types with distinct frictional characteristics.


RE: Remote oil cooler on manual transmission

romke, the shifting problems in my Mini Cooper race car can usually be attributed to the dumb ass rowing the shifter about...usually.  Of course the antiquated "remote shifter" of the early Minis is not exactly "state of the art", even for 1963.  As far as the gearbox/synchros...I really have not had a problem, at least with THIS gearbox, a straight cut close ratio synchro box.  Of course I change the lubricant after each race weekend, Redline Racing 50.

As all this relates to motorcycle gearboxes...I have experience with a few, most notably the Hodaka style "ball change" constant engagement type, the early BSA and Norton non synchro and, My KZ which was closer to at true "dog box". All very close ratio, all could be shifted without a clutch with ease...NOT typical of automotive synchro or dog box.  Where a bike can live on just about any lubricant, that may not be the hot setup for a car.

Trust that if I could isolate the Mini's gearbox, it would be using ATF !  AND, NO I'm not even going to try !!! winky smile


RE: Remote oil cooler on manual transmission

That's backwards- MB oils are friction modified and MA oils typically aren't.  

Actually, MA oils (subsequently split into MA2 (higher) and MA1 (lower) classes) have high friction suitable for wet clutch applications, and MB oils have lower wet clutch friction which typically makes them less suitable (though OEMs can spec whatever class they choose to).  Traditional 'friction modifiers' _reduce_ static friction, so MB oils typically contain high doses of these.  

There have been papers published describing friction _increasing_ modifiers in motorcycle oils, so describing either performance classification as containing or not containing FM ingredients may not be accurate.

RE: Remote oil cooler on manual transmission

The gearbox modification has been done. I've sited an oil "suction" pipe from a position near the bottom of the casing and the return outlet near the top.

I've fitted the return flow outlet where it should avoid throwing oil at meshing gears; I am concerned about causing undue aeration of the oil. I've decided to slow the pump, too. The reason for this is that in standard form it can move 3.7 Imperial gallons per minute and the gearbox only holds about a pint so it will have a very quick "turnaround time".

For this reason I've taken advice and decided to use Silkolene "SilkTran" oil which apparently has a very good resistance to aeration. I must admit a bias to their products as my grandmother was their company secretary for many years and I know their head chemist. Seeing him stop to oil up the exposed valve gear on his 3 wheeler V twin powered Morgan as a schoolboy was probably one of the reasons I became interested in wacky, off-beat vehicles.

All I have to do now is install it. I'll report back when it's all done and the car is back on the road.

RE: Remote oil cooler on manual transmission

The oil cooler and electric pump are now installed. The pump is wired through a fused relay and a resistor to slow down the flow a little. The relay circuit is triggered by a thermal circuit breaker rated at 70 degrees C, which I've fitted to the outside face of the gearbox casing.

I've filled the box with the Silkolene SilkTran synthetic lubricant, as previously mentioned. It took 25% more fluid to reach the level plug due to the extra capacity of the cooling circuit, which is probably a bonus in itself.

Hopefully there will be nothing more amiss to report so thanks again to all those participating in the discussion.

RE: Remote oil cooler on manual transmission

Hope I do not disappoint you, but as far as I know the lubricant mentioned is (a high suality) SAE 75W-90. That might still give rise to higher temperatures (but it is better then what you used to have), when compared with a high quality ATF.

I suggest you try the Silkolene and if overheating still occurs, try ATF.

Good luck.

RE: Remote oil cooler on manual transmission

Thanks, romke.

Hopefully the cooler will now keep the temperature under control and as you say, the SilkTran lubricant is certainly much better than the plain vanilla mineral based stuff I used before, at any temperature (it must be, it costs much more than best beer per litre. But will hopefully last somewhat longer).

I certainly will try ATF next if there are further issues.

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