1995 K2500 6.5 TD/4L80E with 48 plate external cooler.
I recently went on a pretty good trip to test these things. I had a slide
in camper in the bed driving in southern Ohio (hills) on 85 degree days.
Here is what I found:
1) On the open highway at about 65-70 mph, I saw about 150-170 deg. F
2) On long steep, slow grades and down to about 55 mph, I saw 180-190 deg. F
3) Long steep grades (like in a state park road) of about 20 mph and high
RPMs, I saw 200 deg. F
It seemed that the air flow was the determining factor here, not RPMs. My
higher RPMs would cool the engine temp., but raise the ATF temps. Maybe a
better fan and clutch will help pull the air when I do the '97+ cooling
upgrade this fall and I will upgrade to the 72 plate transmission cooler at
that time. I'll try to remember to post back.
I hope this may help some that don't have gauges to watch. Pay attention to
your driving conditions or you'll be going to see Gary much sooner than you