Tow vehicle trans overheating Question

I love my boat. I love my tow vehicle. So far Ive had cooling issues with both. I had to replace the trans in my Nautique 2001 because I neglected to replace the impeller on the water pump. But now Ive got problems in my 91 Suburban. The 4l80e should handle my little boat, but Ive seen 260 degrees a few times on the trans, even after aftermarket coolers and high capacity pans. So I checked the flow to the coolers, and it seems to be reversed? Coming out the bottom line to the trans, from the coolers, when it is supposed to be the other way around?

Anyway, all these stupid problems are keeping me from learning how to ski, because I spend more time under the hood of my boat and truck then in the water.

I believe I've got the 4L85e in my 6.5 turbo. My uderstanding is it's a slightly modified 4L80e. I have never had any cooling issue's and have 230K on it.

Eric,
Do you know what mods were done to the 80 to make it an 85? I know the RPM shift points are lower due to the diesel.

I measured the flow, and from what I can tell its about half a gallon in the ten seconds I ran it. I just hooked up the coolers reversed from what I had it, so now it goes through the radiator first, then the aftermarket cooler. I also replaced my el cheapo gauge with a nice B/M gauge, mounted in the pan rather than the test port of the trans. I read a steady 180 degrees for over an hour while towing on flat highway speeds. But, as soon as I hit a good sized climb, in went to about 250. My heart sank. My boat doesnt weigh as much as the ToyHauler Im allowed to borrow. Also, how close should the aftermarket cooler be to the radiator? Ive got about an inch or 2 gap between them.

i think your chasing your tail with the cooler situation, one is sufficient and you added....plenty of cooling capacity, all the whackjob tranny guys always tell me you have to change the valvebody or you will have cooling problems...must be something to it, search some 4L80 trans forums, im sure you will find similar complaints and problems

it went 350 turbo, 400 turbo, 700r4, 4l60e, 4l80e I'll check Pete, im not familier with a 4l85