Transmission Cooling ideas - Air Versus Water

[Rob T]

I have a 6MT that is seeing some of the heating issues Gator talks about in the 818R section. My car is strictly a track car and typically runs 20 minute sessions. I have been thinking about two options for cooling the transmission I have, which is old enough to have the internal oil pump that can be re-routed to a cooler (like Hobby Racer). In addition to the air to oil design HobbyRacer had developed (others, too), I was considering using a marine, oil to water tube in shell and using the return of my AWIC system as the "water". I'd like some comments on the idea, please. Here is what I see as of now....

Advantages
1) Compact and easy to mount next to transmission.
2) Simple to route hoses, etc.
3) System already exists - it does not take any additional controls or electrical work.
4) The thermostat block HobbyRacer has identified would not require any electrical or other work.
5) Pressure drop would be minimal and head change (due to height) could be virtually eliminated by keeping the tube in shell low relative to the transmission - it could stay flooded.
6) These heat exchangers are "robust" from marine duty.
7) Don't have to duct air to the cooler or change the airflow through the engine bay.

Disadvantages
1) Transmission fluid and water are now being passed by each other.
2) This ties the AWIC system to the transmission heat load. It is unknown if the front mounted radiator has enough capacity to handle the extra heat. Currently, my IAT's are ambient +10F. I don't want to mess that up. Clearly, the water would flow from the radiator to the AWIC to the transmission cooler back to the radiator.
3) The transmission could operate well over 212F at times, based on current data, pressurizing the AWIC system, which does not really happen now with just the AWIC load.
4) While the new tube in shell will add a bit of pressure drop, it should be minimal as the water passages are quite large.

What do you guys think of the idea (not original, I am sure) and what am I missing?

[Hobby Racer]

I think its a solid idea. Tho only issue I can see is that you will heat soak the AWIC system much quicker than before. I am not sure if your short 20 minute sessions will be an issue or not. You will also have to wait longer between sessions to bleed off any excess heat.

But again, this is only speculation. I use an oil to water cooler for my engine oil and I love it! I never have temp fluctuations and as a bonus the oil heats up quicker during my first session.

I would go for it. If the heat load is too much for the AWIC radiator you can always tie it into the engine coolant return line so the setup would not got to waste.

[Rob T]

One thing I forgot to mention. One of my two radiator fans is on a switch and I have a manual switch for the AWIC pump. So....I could run one of the fans and circulate the AWIC water while sitting in the pits after the session. A battery drain, for sure, but possible. The AWIC radiator is first in line, in front of the cooling system radiator.

[Sgt.Gator]

Do you have a temp sensor/gauge/datalogger in the AWIC Coolant line?
I too would be concerned that the extra heat load would shorten your track time for the AWIC to be effective.

[Mitch Wright]

What if you source the water from the engine using the heater inlet and outlet? As Gator mentioned I wouldn't want to add additional heat to the AWIC.

[Sgt.Gator]

Expanding on Mitch's comment....You could do similar to Dom's Cyl #4 cooling mod and kill two birds with one stone. Take the coolant out of the back of Cyl #4 and route it thru your Marine cooler., then back into the cooling system thru the heater bypass U hose. The water would be pre-heated to whatever temp is coming out of the engine block so it wouldn't be as effective for the trans...but I think it would be worth a try. I bought a bunch of the JDM Subaru Twin Turbo Legacy Plug-Water Bypass parts, 21170AA020. I'll be happy to send you one if this is the route you want to try.
You'll need this part and a T to put the return water back into the heater bypass hose. I use the Dorman 56387.
21170AA020 B.jpg
21170AA020 A.jpg

Dorman T 1.jpg
Dorman T 2.jpg

[Bob Cowan]

Heat is energy. Every time you transfer energy/heat from one medium to another, you lose some efficiency. Going from oil to water to air will be less efficient than oil to air. You're adding more complexity and weight than you need.

[Bob_n_Cincy]

Heat is energy. Every time you transfer energy/heat from one medium to another, you lose some efficiency. Going from oil to water to air will be less efficient than oil to air. You're adding more complexity and weight than you need.

The reason for AWIC systems and water cooled engines all has to do with taking the heat to the place with the best air flow. Very few vehicles are running air cooled engines these days. My 500cc atv and 1000cc side by side all use liquid to transfer heat to the radiator/exchanger.

[mike223]

The reason for AWIC systems and water cooled engines all has to do with taking the heat to the place with the best air flow.

Excuse a question from a roadster guy - but I was wondering about this yesterday (but didn't post).

Is there any way to take the airflow straight to the transmission? - like maybe using a separate electric radiator fan to direct cooling air across the transmission housing?

Just a thought...

[Hobby Racer]

Excuse a question from a roadster guy - but I was wondering about this yesterday (but didn't post).

Is there any way to take the airflow straight to the transmission? - like maybe using a separate electric radiator fan to direct cooling air across the transmission housing?

Just a thought...

That can certainly be done, but you get more efficient cooling via a radiator instead of cooling the transmission case and then the oil via convection. The trans case is a pretty big heat sink and holds the heat more than the very thin fins and tubes of a radiator.

[Bob_n_Cincy]

Excuse a question from a roadster guy - but I was wondering about this yesterday (but didn't post).
Is there any way to take the airflow straight to the transmission? - like maybe using a separate electric radiator fan to direct cooling air across the transmission housing?
Just a thought...

I tried a rear radiator with big fans on my 818.
rear_rad.jpg

It was Unsuccessful. The fans only generated about 10 mph air. The front of the car generate 130 mph when at full power.
With the rad in the front my fans never turn on while on track. Going to the paddock to the pit the fans kick on every time.

On a standard Subaru, most air coming through the rad exits through the transmission tunnel. The air is heated from rad and exhaust pipes, but it is still cooler than the transmission. The 818 cockpit blocks any of this airflow.

Bob

[Sgt.Gator]

On a standard Subaru, most air coming through the rad exits through the transmission tunnel. The air is heated from rad and exhaust pipes, but it is still cooler than the transmission. The 818 cockpit blocks any of this airflow.

Bob

When I flat bottomed my STI and went to a hood vent that draws most of the air entering the front thru the radiator and FMIC, and out the top of the hood, was when I started melting plastic electrical connectors on my six speed tranny. The heat from the downpipe was too much for them, an issue I never had before that. We had to add a bunch of extra heat shielding to wiring anywhere near the back of the engine and the transmission.

[DanielsDM]

What if you source the water from the engine using the heater inlet and outlet? As Gator mentioned I wouldn't want to add additional heat to the AWIC.

I've been considering doing this. I think it might work well. If the coolant temp leaving the motor is 180 or less it may keep the trans oil temp under 200. I'll have to build it and test to know for sure.

[David Ferguson]

A car on a race track has high-speed, high-pressure cool air available when it needs it. A marine application has cool water available when it needs it. You should definitely use air-oil coolers with your transmission for a track car.