ELECMAN

I want to install a tranny cooler in my cutlass i have a th400 tranny a older gentleman told me that you should run the tranny lines straight to the cooler and bypass the radiator because if the radiator is hot its making the fluid run hot is this true or put it in series with the radiator

rustyroger

My local transmission shop and the instructions supplied with all the kits I have bought (I install a trans cooler on every car I own as they will have caravan towing duties) recommend installing this way;
Mount the cooler in front of the coolant radiator & A/C condensor, preferably fabricating a stand alone bracket rather than using the ziplocks supplied,
Run the hot transmission line to the new cooler,
Return it to the original hot fitting on the coolant radiator.
This is to avoid overcooling the trans fluid, remember it has an optimum operating temperature, alternatively fit a bypass thermostat, I have been told fitting a 'stat is not really necessary for my requirements, possibly if I was in using the car in a more extreme climate (very hot summers & very cold winters) a thermostat might be a good idea.
I have never had issues with my transmissions (GM, Ford, Mopar and BW) doing it this way.
I have asked on several forums what the consequences of overcooled fluid might be, several replies show charts showing expected transmission life at various temperatures but none indicating what may happen if it consistently runs very cool (below 140f). Any transmission experts able to give a comprhensive reply?.
Roger.

jag1886

You are suppose to run the pressure line from the transmission to the radiator first, then through the external cooler, then back to the transmission.

joe_padavano

I've done it with and without the radiator in the loop and found no difference in performance.

TripDeuces

You can never have the trans temp too cool. Unless of course it solidifies to jelly. There is no optimal temp for tranny fluid. If you could keep it between 140-160 it would last forever.

Olds64

I would use both. Your radiator shouldn't be too hot anyways.

rustyroger

My GM transmissions have all worked fine from cold, as did the AOD in a Lincoln and the 727 in a Dodge truck. I seem to remember a BW65 in a '70 Jaguar and an '86 Nissan Sentra shifting up slowly until they warmed up a little.
Roger.