Trans cooler fliud route

Mark Kovalsky wrote:

BenK wrote:
Another of these never ending opinions...

But my opinion has 19 years of automatic transmission engineering data collection backing it. The last three years I was responsible for transmission cooling.

BenK wrote:
Most all OEM setups has the ATF go to the external aux first, then into the main radiator

I studied almost every automatic cooling setup that was available. We bought many, many competitive cars and trucks for the engineers to examine and see what all the other automakers were doing. I NEVER found one that had the aux cooler before the radiator. Not a single one.

BenK wrote:
ATF needs to operate in a range...can be too cold or too hot (worse)

That's true.

BenK wrote:
It needs to see a min temp in order to get rid of over nite condensation, so has to see the main radiator coolant temps before going back to the tranny

I know that is what many people believe, but it isn't true. I tested this in temperatures as low as -40. The radiator NEVER warms the ATF. Ever. In any conditions that I could find. It isn't even close.

I measured temperatures in the ATF line into and out of the radiator. I measured coolant temperature inside the radiator, near the transmission cooler. I measured coolant temperature into and out of the radiator. There were usually 100 thermocouples on the vehicle when I ran one of my tests.

In hot temperatures you could ALMOST make a case that the radiator would warm the ATF. Not quite, but the temperatures of the coolant and ATF were closer than they were cold.

When the ambient temperature gets well below 0, such as -20F to -40F, the coolant in the radiator on the cold side (where the coolant has already passed through the radiator) stays within about 10F of ambient temperature. It is NOT at engine temperature. It isn't even close to getting into positive number temperatures. This is once the engine is warmed to operating temperatures and the engine thermostat is cycling open and shut. It will not stay open because once the thermostat opens the engine takes a big gulp of coolant from the radiator. That coolant is anywhere from -40F to -10F. That cools the engine down below the thermostat close temperature in a very short time. Then the thermostat closes and the coolant stays relatively still in the radiator. The cold ambient air is still passing through the radiator, and the coolant has plenty of time to get back down near ambient temperature before the thermostat opens again for a few seconds and the cycle repeats. I was able to measure this on many different vehicles. The actual numbers varied a bit, but the pattern held on everything I tested.

Since the coolant around the transmission cooler stays below 0F, it does not warm the ATF before it heads back to the transmission.

In later model transmissions there is a transmission thermostat. Ford started phasing these in during the 90's. They bypass the transmission cooling system until the transmission warms up, usually to around 165-180F.

BenK wrote:
I always plumb my external ATF aux radiators BEFORE the main radiator

As explained above that won't help warm the trans at all, but it will reduce your cooling efficiency. The system is more efficient at cooling the transmission if the hottest ATF goes to the radiator cooler first, then to the aux cooler. That is why all OEMs do it that way.