Transmission cooler bypass installed

[Drcoffee]

Didn’t want to hi-jack another thread but I have seen many members asking about over-cooling the transmission. When I installed a Tru-cool ATF cooler it did a great job keeping me at 160*F while towing a boat last summer. But fast forward to December 2021 and ambient is now <40*F and my tranny is running at 110*F which is too cool to vaporize water condensation within the transmission. So I swapped out the Tru-Cool cooler for a B&M cooler I had laying around and added a Derale thermostatic valve I bought on ebay for $50. The Tru-Cool was too big to accommodate the valve so I changed it for the B&M I think its the 72640 or 76240 model.

The second pic is the larger Tru-cool with a cover blocking air flow. The other pic is the new valve and B&M cooler. The valve has pre-drilled threaded holes to mount it. I used one stainless screw mounted to the AC line bracket with a little blue loctite and lock washer to keep it from backing out over time.

The valve opens at 180*F , but until then it flows 90% thru the bypass valve and 10% thru the cooler to maintain pressure in the system. This seemed like the best solution for adding extra cooling capacity.

 

[Bluesky 07]

Didn’t want to hi-jack another thread but I have seen many members asking about over-cooling the transmission. When I installed a Tru-cool ATF cooler it did a great job keeping me at 160*F while towing a boat last summer. But fast forward to December 2021 and ambient is now <40*F and my tranny is running at 110*F which is too cool to vaporize water condensation within the transmission. So I swapped out the Tru-Cool cooler for a B&M cooler I had laying around and added a Derale thermostatic valve I bought on ebay for $50. The Tru-Cool was too big to accommodate the valve so I changed it for the B&M I think its the 72640 or 76240 model.

The second pic is the larger Tru-cool with a cover blocking air flow. The other pic is the new valve and B&M cooler. The valve has pre-drilled threaded holes to mount it. I used one stainless screw mounted to the AC line bracket with a little blue loctite and lock washer to keep it from backing out over time.

The valve opens at 180*F , but until then it flows 90% thru the bypass valve and 10% thru the cooler to maintain pressure in the system. This seemed like the best solution for adding extra cooling capacity.

I have a Hayden 698 which is keeping my fluid temps in the 140s. The Derale temp-regulating bypass is a great solution for ensuring the fluid stays at 180° and I plan to install one. But how will determining the correct fluid level work when it's time for another drain and fill (the complete ~12 qt. version)?

I installed the Hayden during my recent exchange, meaning the fluid was flowing through the Hayden and its capacity was accounted for during the level check.

After installing the Derale, the fluid will reach the target range (97° F - 115° F IIRC) with the external cooler bypassed, so its capacity will not be accounted for later when the fluid's operating temp opens up the Derale at 180° F. The capacity is a quart or so. Can the Derale be opened manually? If not, doesn't that mean the transmission will be a quart low any time the external cooler is operating? Any thoughts or concerns around that?

 

[Drcoffee]

I touched on that in the passage you quoted me on. There ia always a 10% flow going to the cooler. This moves any air out of the cooler. I have the inlet at the bottom and exit at the top of the cooler. So by the time the trans reaches 110*F the cooler will be full. Anytime you add a cooler you need to verify the correct fluid level. There are other bypass valves out there but I chose Derale because it allowed fluid flow to the cooler even when cold.
Im not concerned at all.

You could also purge any air in the cooler before checking the atf level by simply removing the upper hose until atf comes out.

 

[UrbanRunner651]

Any reason you ran the return line from the top? Wouldn't you want your return line feeding from the lower outlet to ensure it drains as much fluid as possible?

Bluesky, I had similar concerns about volume drop when in an open state. I reached out to Hayden for specs and eventually got them to give me an accurate volume for the 698 which is only 5.8oz (<1/4qt). Plus the length of your new lines which are 0.5oz/inch for the 11/32dia. After install I added 12oz & drained about 4-5oz during level check.
The variance between bypass & open states should be negligible in that case since the trans should be able to handle +/- 0.5qt

 

[Bluesky 07]

I touched on that in the passage you quoted me on. There ia always a 10% flow going to the cooler. This moves any air out of the cooler. I have the inlet at the bottom and exit at the top of the cooler. So by the time the trans reaches 110*F the cooler will be full. Anytime you add a cooler you need to verify the correct fluid level. There are other bypass valves out there but I chose Derale because it allowed fluid flow to the cooler even when cold.
Im not concerned at all.

You could also purge any air in the cooler before checking the atf level by simply removing the upper hose until atf comes out.

Right, the constant 10%. My bad for missing that.

Thanks, [MENTION=172840]UrbanRunner651[/MENTION], that information is very helpful as well.

 

[Drcoffee]

Any reason you ran the return line from the top? Wouldn't you want your return line feeding from the lower outlet to ensure it drains as much fluid as possible?

Bluesky, I had similar concerns about volume drop when in an open state. I reached out to Hayden for specs and eventually got them to give me an accurate volume for the 698 which is only 5.8oz (<1/4qt). Plus the length of your new lines which are 0.5oz/inch for the 11/32dia. After install I added 12oz & drained about 4-5oz during level check.
The variance between bypass & open states should be negligible in that case since the trans should be able to handle +/- 0.5qt

Are you sure about 0.5 oz/inch. I think you meant foot.

My best guess is the factory runs the fluid in the top out the bottom because the radiator is colder at the bottom. But in the trans cooler, I believe Im purging out the air when the fluid flows from the bottom up. Im not sure it matters but it seems to cool more efficiently in my experience.

 

[Bluesky 07]

[MENTION=78997]Drcoffee[/MENTION], do you have the p/n for the Derale you used? TIA.

 

[Drcoffee]

Derale Transmission Oil Cooler Thermostat 25011

3/8” version

https://static.summitracing.com/global/images/instructions/bmm-bm_cooler_techdoc.pdf

 

[Drcoffee]

Im glad to report that this bypass works as promised. In the cold of the winter tranny rises to 140-150*F and in the summer pulling the 21’ boat only reaches 165*F.

I noticed that the aluminum housing was oxidizing with white powder, so I suggest painting it before the install. A little rustoleum rattle can does a nice job.

 

[Bluesky 07]

Same here. I had my OBD Fusion app monitoring the temp on a 95 degree day and could see the result when the bypass valve opened. Temp would rapidly drop from ~190 to the low 170s.

 

[iamatt]

Bypassed mine with a cooler someone gave me worked at U-Haul. Made it fit, 180F switch and some fans. Haven't ran hot once since. We bomb the beach, NASTY sand for tens of miles. One less thing to worry about now.

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