Remote oil cooler on manual transmission

[PEW]

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.

 

[MikeHalloran]

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

 

[patprimmer]

Run copper, aluminium or steel line to the filter and use a finned aluminium filter body and you might not need a cooler.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[IceStationZebra]

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.

ISZ

 

[patprimmer]

Have you looked under the front of an old Porsche 911 recently or at many of the OEM Power Steering oil coolers.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[romke]

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.

 

[evelrod]

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!

Rod

 

[PEW]

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.

 

[PEW]

I see my ATF question has also been partly pre-empted by evelrod, Thanks for that!

Here's a link to a picture of the engine /gearbox:

 

[amorrison]

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.

 

[PEW]

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

Regards, PW.

 

[IceStationZebra]

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)

ISZ

 

[vwhammer]

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
Bill

 

[evelrod]

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 !

Rod

 

[PEW]

"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.

 

[PEW]

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. ;-)

Paul W.

 

[evelrod]

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?

Rod

 

[PEW]

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.

 

[evelrod]

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.

Rod

 

[PEW]

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.

Paul W