Heating the transmission with engine coolant

[gone-ot]

Recondition: heater control value from wreck

[Gasoline Fumes]

Originally Posted by Daox

Why would you want to use an additional electric pump (and thus another load on the engine), when you could just use the coolant pump that is already on the car?

The reason I suggest pumping the trans fluid to a heat exchanger is because I don't think you'll find enough usable surface area on a trans to get a decent heat transfer.

[user removed]

Lots of car companies use fluids other than gear lube in trannies. Chrysler used atf in it's manuals in the 1960s. BMW used mineral oil in the 70s, learned that one the hard way. A simple fluid change may give you the most benefit for the least cost.

Try some other fluid like atf, your driving conditions are most extreeme but not on tranny fluid. Is there any risk? Of course, but given your imposed limitations I would try that first.

regards
Mech

[Daox]

I'm still digging for info. In this paper, I found this info. This only pertains to the bearings in a gearbox, but it shows substantial reductions in power loss due to increasing the oil temperature, and that is with the gear oil starting at 40C / 104F, and compared to 80C / 176F.

[Daox]

Here is some more info from this paper. Take note this test was done at 9000 rpm! So, losses at a lower rpm should be less. However, the temperature differential is pretty small. 22C / 72F to 28C / 82F.

[Daox]

And, one more. I believe this test was done on a single gear set (just two gears), not a whole gear box. So, the power losses should be lower than in a automotive transmission. However, this is the best data I've found thus far. It gives a range of temperatures tested, and at speeds we would see in our application.

By looking at this chart, it looks like at 2000 rpm, increasing oil temperatures should be able to very roughly half the losses to the transmission.

[ECONORAM]

We used to own a 2004 Ford Taurus, and I noticed n winter the tranny would not hit OD as earlier as the summer. I only had a 5 mile commute to work. I learned the tranny has a temp sensor that prevents the converter from locking when the fluid is too cool. So, in the winter I used a little space heater on a timer, pointed at the tranny It would run for about an hour, just prior to me leaving for work. Warmed things up enough to lock the convert just like summer.

[sqidd]

Man, that sure does seem like a LOT of work for very little if no gain.

On a basic level you are trying to heat the trans fluid up so it is "thinner" right? So why not attack it from the other direction? Run "thinner" fluid to start with? The down side to that of course being that when it is hot out it may be too thin. But it wouldn't be too hard to figure out the balance. What did you say that trans took? 75/90? Man, that is some serious fluid for a manual trans. Most stuff runs ATF now. You could probably run a real good synthetic ATF or at least a low viscosity synthetic gear oil and probably replicate "hot" standard gear oil really well.

Back in the day we used to run GM Syncromesh in transmission that took gear oil in racing applications (heavy load). Stuff worked great and is a lot "thinner" than gear oil.

Here are some viscosity #'s for the different fluids:

ATF 6.5-8.5cst
Syncromesh 9.5cst
75w85 9.8-11.5cst
75w90 12.8-14.5 cst

Switching form 75w90 to 75w85 is a pretty big jump (about 22% average)

Switching from 75w90 to Syncromesh is 31%

I'm not sure you will see a 22-31% decrease in "drag" by pre-heating your current fluid.

Just a thought.

[Daox]

Well, thats what we're trying to figure out here. Is it worth it? Is it a waste of time? I dunno. Its just an idea I'm throwing out for us to discuss.

Those viscosities are probably at 100C. I don't even think my trans will get anywhere near that on my 7 mile commute.

Here is another study:





There is also this very interesting graphic. Note the tests were done at 100C transmission temp.

For reference (from here):
Kinematic Viscosity @ 100°C, cSt (ASTM D445) = 16.6
Kinematic Viscosity @ 40°C, cSt (ASTM D445 = 129.7 87.6

The viscosity change from cold to hot is a heck of a lot more than 13%. So, I can only imagine, in the first few minutes of driving, we are seeing a pretty substantial hit simply from low transmission temperatures.

[sqidd]

Originally Posted by Daox

Well, thats what we're trying to figure out here. Is it worth it? Is it a waste of time? I dunno. Its just an idea I'm throwing out for us to discuss.

Yep, I getcha. I spend most of my days kicking some crazy idea around.

Here is some food for thought:

Back in the day when I was racing the AMA Factory Honda Supersport bikes ran this crazy blue oil that I was told by their engine guy was 2.5w. That lubes the motor and trans.

My F-150 has so much drag from the diffs, T case and trans when it is cold out I will be down 2-3mpg for the first 15-20min of driving.

You are making such short tips I would really consider the "thinner fluid" route. You can always check the trans temps if you are worried you went too thin. As long as the trans stays under 200deg (which is still real safe) you're good to go.

Good luck!