Which way does transmission fluid flow into radiator?

Probably a stupid question. I have a '22 TRD OR, which does not have the external air transmission cooler. Therefore there are two rubber lines running into the radiator. My question is does the fluid flow from the bottom fitting to the top? Or the other way around?

 

The bottom hose is the one you want. When I put in my aux cooler I ran a line from the bottom of the radiator to the top of the cooler and then ran a line from the bottom of the aux to the return line that you took off the radiator.

 

If I'm understanding you correctly, the transmission flows like my drawing and that is how you would want to plumb the cooler in?

 

If you are installing an auxiliary trans cooler, why bother with the cooler in the radiator? Why not just bypass it? If your intent is to cool the fluid, why expose it to the 200+F deg. engine coolant?

 

I was just trying to make it as OEM as possible?

 

Yes your drawing is how I hooked mine up. I added my aux cooler because I tow a Trailer with my truck and it keeps the temps in the acceptable range.

 

I'm guessing that whichever cooler you may install, it's probably going to take ~ 1/2 quart or so of fluid?

 

Probably. I did mine at the same time I did the tranny service.

 

I believe it uses the coolant radiator to get the transmission fluid up to temp at cold start. I think even the OEM auxiliary transmission cooler still goes through the radiator.

 

I have towed for many years with several different cars and trucks. I installed aux external transmission fluid coolers on most of them and they were always connected in series to the bottom outlet of the factory in-tank radiator cooler. (return line to the transmission) I called Hayden about this one time and they advised to connect it in-series that way, after/down-stream from the factory the tank cooler, and not to by-pass it. I didn't ask why but the idea of helping with initial winter warm-up makes sense.

 

Yes. ^^

The transmission's fluid trip through the radiator is to both warm the fluid and to cool the fluid. Warm it up from cold as fast as possible at first. It is Toyota's opinion the transmission should not run cold for long. The radiator will also cool excessively hot fluid to a lower temperature.

I'm just going to put out some numbers here for a comparison, they may not be accurate for your use. The coolant temp may be between 160-190 degrees normally. When the trans fluid gets up to 220-240 or more the radiator will cool the fluid down.