Trans cooler fliud route

LVJJJ wrote:
Although I've been towing for years, and have always had a transmission cooler on every tow vehicle, I can't remember whether the fluid should come from the trans thru the cooler then to the rad and out back to the transmission, or vice versa?

In other words before or after the the radiator?

Recently purchased an '04 GMC Envoy to tow our 4000 TT, has tow package but no cooler. On the Trailvoy forum, there didn't seem to be a consensus as to which way it should be. Since those using their Trailblazer or Envoy for towing was a minority, I'm thinking us RV'ers here would know best.

The climate you live in seems to be the reason for placing the cooler before or after?

IMO the typical OTA aux or OEM cooler should be plumbed AFTER the OTO (i.e. radiator type) cooler. This is because the OTO is much more efficient in removing heat from the transmission fluid but will never have a cooling fluid (i.e. antifreeze) cooler than the air used for the cooling temp in the OTA cooler. Thus you remove as much heat as possible with the more efficient OTO cooler and then try and cool it as close to ambient air temps with the OTA cooler. AFAIK this sequence is used in FORD vehicles and I would be somewhat surprised if other OEMs didn't use the same sequence in their transmission cooling systems.

Finally, I think factors such as the increased cooling at speed from the OTA coolers and such things as the cooler differential temps and heat transfer factors also play into why one cooler should generally be before the other, but that is way above my paygrade or desire to really fully understand.

Larry