Heating the transmission with engine coolant

[Daox]

It doesn't get a ton lighter than the Tercel haha. It weighs in at 1925 lbs.

The current mod for the trans I'm looking at is dropping an automatic's 4spd differential gearing in it. The extra 5spd manual Paseo (which is what I have laying around) trans has a stock 3.94 diff ratio where as the automatic has a 2.82. I still have to verify that it'll physically fit. If it does, that means I'll be running just under 1400 rpm (vs 1940) @ 45 mph and 2000 (vs 2800) @ 65 for the freeway drivers.

[pjbgravely]

That is strange. In the old days automatics had a lower ration so using an automatic gearing resulted in higher engine speeds.

I like your idea. I was designing a belly pan to achieve the same thing by letting the exhaust pipes heat the transmission in a rear wheel drive. I have yet to complete it but I think it would have needed a louvered lower grill block to allow the engine to actually heat up before 10 miles.

Personally I would use an electric block heater to preheat the engine and trans-axle if electricity is cheap where you live. Finding a way to heat the trans-axle with coolant is the real challenge.

[user removed]

I just looked at my Sentra. The radiator is a top-bottom tank type, not crossflow.The reverse flow cooling system feeds the hottest coolant to the transmission cooler which is in the bottom tank, exactly the opposite of normal. This heats the cold transmission fluid and warms it up instead of cooling the fluid. Once the transmission reaches a temperature above the 169.7 (76.5C) thermostat opening point then the transmission fluid is cooled to maintain a consistent temperature.

In regular flow systems the transmission fluid cooler is in the opposite location, where the coldest fluid in the radiator is located.

There it is "heating the transmission fluid with engine heat" in 1992.

regards
mech

[oil pan 4]

Originally Posted by Old Mechanic

There it is "heating the transmission fluid with engine heat" in 1992.

My suburban came with it. And that was 1984.

[user removed]

Originally Posted by oil pan 4

My suburban came with it. And that was 1984.

A reverse flow cooling system?

regards
mech

[Daox]

Has anyone ever seen this on a manual transmission?

[mcrafarm]

If you have a garage with a gas dryer, you could dry clothes in the morning and preheat the tranny and block using the waste heat diverted using a HVAC flex hose. I'm thinking more of the life cycle energy, using some heat you generate anyway in the morning. Any other such heat sources? Water heater?

[paulgato]

Originally Posted by Daox

You make very good points and I don't really disagree with any of them.

If I were to go the thermostat route, I'd probably use a lower temp thermostat though, say 160F. This would ensure that the trans thermostat opens before the radiator thermostat even begins to open up.

That all being said, where could one get a stand alone / inline thermostat housing?

I did a Google search for "inline thermostat housing car auto" and turned up a few...

RANGE ROVER P38 4.4/4.6V8 - In-line Thermostat and Housing Assembly (PEM101130) | eBay

...this being one of them. Seems inline housings are used in Range Rovers, maybe Jeep Cherokees too. But anyway they seem to be available. The Range Rover one seems to be nice and compact, although I'm not sure why it has three spiggots and not two.

[Edit...] Or this one...?

http://files.qedmotorsport.co.uk/k-s...at_fitting.pdf

...but I still think the gearbox will neither know nor care about a difference of 10 or 20 degrees at around about engine temperature. I wonder if Toyota have tested their gearboxes towing a caravan up a mountain out of Death Valley. Vehicle manufacturers tend to test at extreme temperatures because they want their vehicle to be sold into every market world-wide. (The Taliban used to use Toyota pickups in the desert of Afghanistan I believe. That's some kind of endorsement I guess.)

[maxfnz]

All

Quick 2c here:
- Auto transmissions usually have heat exchangers to the engine radiator (eg inside a header tank) for two reasons - faster warm up when cold (engine warms faster usually) and then to dump heat from the oil (cavitation heating of the oil in the torque convertor, friction). Any thermostat is usually just to stop the oil being over-cooled.

- Manual transmissions probably won't benefit from a heater siimply because of the oil viscosities ... most manuals specify a monoweight oil (80, 90) and if multiweight (80-90 or say 75-140) then it's going to get **thicker** as it heats, not thinner. Surely in that case you need cooling, not heating?

Maybe a manual might be specced for a monoweight oil by the OEM, and if so then going to the lowest for your running temperatures would be an advantage. My call would be to err on the side of caution - most gearboxes are 100% splash lubricated (some will have catch channels to gather spray & duct it into bearings too) so getting it wrong will lead to less average lubrication & so friction losses & wear.

HTH

Max
(old guy who's played with too many European cars with hot automatics and too many noisy motorcycle crash gearboxes )

[Daox]

Originally Posted by maxfnz

- Auto transmissions usually have heat exchangers to the engine radiator (eg inside a header tank) for two reasons - faster warm up when cold (engine warms faster usually) and then to dump heat from the oil (cavitation heating of the oil in the torque convertor, friction). Any thermostat is usually just to stop the oil being over-cooled.

Thanks Max! This leads me to believe I'm not totally off base here. Though I have no doubt that the manual trans will have less gains from heating the fluid than an automatic trans.

- Manual transmissions probably won't benefit from a heater siimply because of the oil viscosities ... most manuals specify a monoweight oil (80, 90) and if multiweight (80-90 or say 75-140) then it's going to get **thicker** as it heats, not thinner. Surely in that case you need cooling, not heating?

This isn't completely true. Lets use 75W-90 for example because that is what is called for by my transmission. As we all know, 75W90 oil acts like a 75W when cold, but 90W when hot. So lets pull the specs from the amsoil site:

Kinematic Viscosity @ 100°C, cSt (ASTM D 445) = 13.9
Kinematic Viscosity @ 40°C, cst (ASTM D 445) = 87.6

As you can see, the 75W90 oil is still a lot thicker at 40C than it is at 100C. This is because oil thins out as it warms up, and 90W is thinner at 100C than 75W is at 40C.