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Originally Posted by RockyMtnRay
It wouldn't hurt...but if you don't tow, it won't help a lot either. I have both coolers and a pan mounted transmission temperature gauge and the highest I've ever seen the pan temperature when not towing is 150 (on a 95 degree day, in heavy traffic, while climbing long and steep hills). The external cooler only works when at speed (over about 40 mph)...at low speed the cooler in the radiator is doing all the cooling...and I only see about a 10 degree difference. The external cooler is really just a supplement to the internal cooler. I should add that ATF is quite stable and long lasting as long as its temperature does not stay above 175.
One of the reasons that the '03s/'04s don't have an external cooler unless you have the towing package is that the transmission cooler in the radiator is very effective for regular driving.
Only if you tow...actually only if you tow a fairly heavy load in high temperatures on hilly/mountainous terrain and can't keep the transmission's torque converter locked...does the ATF pan temperature rise above 175 with both factory coolers. I do extreme towing...4000 lbs up 10 mile long 7% grades with the engine at 4200 RPM in 2nd gear the whole way. Highest temperature I've ever seen my transmission get to was still only 195 and that was with 90 plus ambient temperatures.
For ordinary, non-towing (or even light towing) driving, any external cooler is more feel-good than useful.
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Thanks RockyMtnRay for your informative post. I'm going to just head out and nix the cooler. I see your point in that a 7" x 7" cooler will not help much until you operate at a significant speed and since my trailer is in the "small" category, I'll "chance" it. B&M makes a thermostat operated unit w/fan that probably puts the OEM Toyota unit to shame and it is 1/2 the price of what Toyota wants for theirs. A service technical that works for Toyota told me "off the cuff" that the Tundra tranny coolers were crap compared to other truck brands and aftermarket units so you can see how I was beginning to get confused by the conflicting information I was getting. Your post made sense to me and I'm going to just head out. I would like to order the B&M or Derale fan units but I don't have time before I leave. The truck has only 10K on it and it is 1 year old. If I screw up the transmission, I'll let Toyota repair it then sell it as I want an O5' anyway. Again, thanks for the great advice!
P.S. To the moderators--thanks for the information about "moving my original post." Might I suggest that an email be sent to the person originating the thread simply denoting that it has been moved (and to where). To be honest I never even thought to look in the section where it was moved but appreciate you informing me that that's where the original went. I just got through reading the posts to it (also very informative) and you can simply "kill" this one if you want to and don't worry about having to merge them.