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Old 05-12-2021, 06:26 PM   #1
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Trans cooler thermostatic bypass valve

I have a 1998 Safari Sahara with a CAT 3136b and an Allison World MD 3060.
The transmission used to run around 220 degrees on flat highway while towing a toad.

So I installed a trans cooler that I pulled off of a school bus with an Allison transmission. The cooler measures 12"h x 20"w, with 6 crossflow tubes, and 1" inlets.

After installing the cooler, the transmission only heats up to about 130 degrees in the summer and barley comes off of the bottom peg. The engine also runs cooler. Sooooooo .......

Has anyone installed an additional cooler and installed a thermostatic bypass valve to get the tranny up to operating temps, but keep it cooler? What valve did you use? Where did you get it? I have looked around a bunch, but I only find bypass valves for diesel pick-up trucks.

Thanks in advance!

Alex
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Old 05-12-2021, 06:50 PM   #2
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Questions ?

What chassis is your coach built on ?

Any idea if the trans temp gauge , is using the Allison trans temp sensor in the valve body , or a sensor elsewhere in the fluid system ?

Is the factory trans cooler an " oil to water " type in the lower rad hose ?

EDIT: What temp is the engine running at ?
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Old 05-12-2021, 10:37 PM   #3
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You would want to add cooler in parallel and use a hydraulic solenoid valve on bus cooler side. Careful not to add any restrictions to OEM. Add a thermostatic switch to open at set temperature, maybe an override switch to force it open from dash, would be nice for stop and go traffic. This should be safe set up. People with hydraulic fans have gone to Wax valve due to factory electric pwm controllers being erratic and failing. Keep it simple.
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Old 05-17-2021, 12:57 PM   #4
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Quote:
Originally Posted by Skip426 View Post
Questions ?

What chassis is your coach built on ?

Any idea if the trans temp gauge , is using the Allison trans temp sensor in the valve body , or a sensor elsewhere in the fluid system ?

Is the factory trans cooler an " oil to water " type in the lower rad hose ?

EDIT: What temp is the engine running at ?
This is a Safari Sahara built on a Magnum Chassis. I am not sure where the trans temperature sensor is located. Yes the factory original cooler is an oil to water cooler in the lower radiator.



The additional cooler that I added uses the two additional ports on the bottom of the Transmission. One marked "To Cooler" the other has a return arrow. Both of the ports had factory plugs in them before I installed the additional cooler.

The engine runs just over 190 and the Trans runs at just over 200.
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