Every time I pull trailers with my truck, it starts to get a little warm. It usually stays right on the 190 mark but now it will go all the way over to the last white mark and hover around right below it. Is this normal? What can I do to fix this?

 

I had that problem as well. Finally installed a cummins 180 Thermostat and it fixed the problem.

Bob

 

I too think the Cummins 180* T-Stat is excellent. PN 3967195.

Also, make sure radiator is clean. Do a search for LOTS of feedback. Good info here...
https://www.dieseltruckresource.com/...ad.php?t=70392

RJ

 

The most common causes of overheating while towing are (in no particular order):

1. Defective thermostat (a properly operating 190 will work just fine)

2. Defective fan clutch

3. Oil-fouled radiator from engine breather catch bottle.

Rusty

 

mine runs just under the 190 when not towing, and right around 190 when towing. Not much difference here.

The only time it went up much was one day I went up the baker grade in california, 17 miles long, and it was 119 degrees. At that point I believe the coolant temperature was at 200 or 205, but I watched it like a hawk to see if it was going to go way up there or just a little. At the top of the grade it went back down to where it belonged.

 

Borrow someone's infrared heat gun. This will immediately tell you the hot spots and whether the thermostat is working. Next, pull the radiator and thoroughly clean the inside and most importantly the outside. This is a great time to add new fluid and replace all water hoses and thermostat.