1999 3500 4door 4x4 6.5L
I have installed a deep tranny pan, synthetic fluid, heat reducing agent, engine fan/165degree clutch, 4in exhaust and tranny temp gauge on the hot line going to cooler in radiator which then goes to a tranny cooler(all stock) back to tranny. When running truck, (no load) ,in town and at highway speeds, my tranny temp runs pretty close to 220*f all the time. I was told that normal temp is 200-220*f. Ambient temps here are 100*f now and will get warmmer.

I bought the truck to pull my 11,000# boat that I usually haul 40ml to the lake. I do have to climb over quite a few hills to get there and back. The ECT's are 180-210*f. The temps that I was running yesterday got me pretty worried. Tranny temps ran consistantly 220*f-300*f.

I have read where someone installed Max-Cooler from Summit with electric fan. I went to tranny shop last week to have them install a elec. fan on the original cooler, but not enough room between the grill and the cooler.
I have to do something to get the temps reduced.

Has someone installed an after market fan or cooler/fan that fits? I am willing to make a few modifications to make something work without cutting up the grill to bad.

Has your truck always ran that tranny Temp?

If so, maybe the guage is just off.

Or, you might have to add a larger cooler.

You should be able to fit a larger cooler in there.

I would PM MikeL for some advice. He has a tranny shop in Socal and is a very knowledgable guy. He hangs out on the transmission forums.

Yes -- MikeL has a tranny cooler that is supposedly very nice and easy to install. Minimum of 20* less temp on side by side.

Just another opinion, the temp. you are measuring is the absolute hottest the fluid will be, it is buy no means the average sump termperature which is the transmission's working fluid temperature, I would get an accurate trans. sump termperature input value b/4 I decided how much of a problem the temperature really is, does the fluid discolour quickly or easily, that is a telltale sign of overheating, al least on non-synthetic fluids it is, also make sure the convertor is locked at towing speeds, that will cook one real fast if it isn't, as it should be.

Todd.:)