I tow a 33' 10,000lb fifthwheel camp trailer. I have not seen any overheating issues when on the highway or freeway. The engine temp would approach 220 at times, but the engine fan would engage and would drop the temp back to 200 rather quickly. The trans temps were consistently 190 - 210. (OEM Gauges)
Last weekend I took the fifthwheel into the local mountains. The road is typical mountain road, max speed around 15mph for about 15 miles, rough, windy, and about 3000ft elevation change, locked in 1st gear. Engine temps were 200 - 210 with the engine fan engaging at times, but the trans temp kept climbing even with the fan engaged. When it reached 230, I stopped and put in neutral and ran the engine around 2000rpm to see if the temps would drop. No change after 5 minutes, so I put it in 4Low and proceeded in 2nd gear to our destination. The trans temp slowly lowered to around 190 and stayed there the rest of the way. Two questions:
1) Does this sound normal just due to low air flow to the cooler?:confused:
2) I know Mike has a new trans cooler, but has anyone tried a small cooling fan, just for the trany cooler?:confused:

In first gear, the torque converter does not lock. In second gear, the torque converter will eventually lock when using Tow/Haul. So when you were driving slow with your transmission in 1st gear, a lot of extra heat was being generated by the torque converter (not locked). This raised the fluid temps. When pulling steep grades with my 5th wheel, I always try to get the tranny to shift into second (though that is not always possible - as in your case). That way, I know the converter is locked and the temps will stabilize. When you went to 4LO and allowed the tranny to shift into second gear, it sounds like the torque converter locked again (Tow/Haul) and your temps lowered down.

Reading what others have posted about Mike's tranny cooler, it sounds like it will help lower the tranny temps. Another thing I have noticed after pulling trailers with this truck for about four years now, is that once the tranny temps rise, it takes a long, long, long time for them to come back down.

By the way, on a warm day I can get the trans temps to go to 210 degrees just driving the truck by itself around the local hills where I live in SoCal (not in Tow/Haul).

In first gear, the torque converter does not lock. In second gear, the torque converter will eventually lock when using Tow/Haul. So when you were driving slow with your transmission in 1st gear, a lot of extra heat was being generated by the torque converter (not locked). This raised the fluid temps.

I was not aware of this, it probably explains why the engine braking does not help much at lower speeds also with first not locking the convertor.:confused:

Thanks for the info:ro)

I just got Mike's Cooler...HIGHLY Reccommended!!!!!!