when to run a tranny cooler

Always.

allways,I run a stock one for a HD truck on both of mine

like said,if used be sure to flush them good

got a PS cooler and an oil cooler on mine

tranz cooler is stock 85 truck unit,ps cooler is from a 93 DAK v-8,oil cooler is from a 88 police gran fury

have a 7 blade fan and a 3 core rad

all on my 85 truck

I always decided to run one after I completely fried my transmission. However, I have 2 (yes 2) coolers and I think I may have overdone it.

It completely bypasses the radiator but even on the hottest day, my tranny gauge (sender is in the pan) never goes about 170. On a normal day, I'm lucky to hit 140 or 150.

Now I am afraid of keeping it too cool.

eight

You should run the tranny lines from the 2 coolers you have and now back into the radiator. This will help get some heat back into it and also help cool your engine. I have heard the same thing about being to cool.

Consider synthetic transmission fluid also!

Heat is the #1 source of problems for an automatic trans. Synthetics hold up much better against heat and potential breakdown.

Amsoil Universal trans fluid.

I've been using their Universal trans fluid in my 2004 Dodge diesel dually that I tow my race car trailer with and their SuperShift in my race car 904. My trans builder said to keep using whatever I have because it protects very well.
Car is race-only, but converter flashes between 5000 and 5400 footbraking, depending on weather and other factors, weighing 3,540+ lbs. Summertime hot-lapping in the late rounds is what concerns me the most and I have an external cooler also, but bypassing the radiator.

Also consider using a thermostat such as this one to keep the fluid at operating temp:
http://www.summitracing.com/parts/PRM-1070/

The ideal set-up is an oversized/large trans cooler before the "in-tank" cooler that maintains the "running-temp" of the returning fluid to the trans.

Heat is the greatest nemesis of an automatic trans.

And as mentioned, too cool is not ideal either, the fluid is not a consistent temp for operation.

Some car makers now use a thermostatic bypass to help the trans heat up its fluid quicker to running temp......something to think about.

thanks i was considering a synsetic what about the cunverter do you have to drain it completely first before filling . wfat about using type f i used it before in my 63 with manual rev valve body ,was told it seals better ....?

I don't think synthetic is going to be a problem. Run your external cooler inline with you're radiator cooler, I run mine into the rad cooler out to the external and back to trans. Type F fluid will firm up your shifts a little.