killed300ex

My 94 2500 CTD is having an overheating problem. Its not bad when I am just driving around empty it will stay right around 190 degrees. The problem arises as soon as I hook some weight behind it start pushing it at highway speeds (truck tows great under highway speeds untill I hit a hill). Getting up to speed you can watch the temp go up then the second you hit any kind of grade you can watch the temp guage skyrocket. This is with only 5000 lbs behind it. I cant even get any power out of it because it just makes the temp go up faster. Wondering if you guys had any ideas what could cause this? I am leaning towards either a stuck thermostat or a cloged radiator?
Thanks
Evan

clutch1

fan working?

dieselfuelonly

Under normal driving conditions does your temperature gauge seem to "bounce" from a little above cold to a little before 190*? That is what it should do, you may be one of the few people that has actually had a thermostat fail closed.

killed300ex

I believe the fan is working not sure about the fan clutch is there a way to check that it is working properly? The temp stays almost perfectly still untill I hit a hill then it climbs fast and then cools down real slow. I am going to try to pick up a thermostat today and change it tonight hope it isnt to big of a pain to change.
Evan

dieselfuelonly

Yeah it shouldn't take very long to switch it out. Sounds like its your thermostat if it stays still, the temp gauge should bob up and down during normal driving, and stick at about 190* when towing. The one on my 2500 is probably stuck, but its stuck open so it just takes a little longer to heat up.

infidel

Most common cause of overheating I come across is from a radiator clogged up with bugs. Sometimes it's so bad the radiator has to be removed for thorough cleaning.
Beware of using high pressure to clean, you can easily bend the heck out of the fins.

If your stat was stuck closed it would overheat even without a load.

CarlJensen

As Infidel said, radiator clogged or fan not working. I use simple green on my radiator and low pressure water. May need to go over it several times. It's amazing how much junk you can get out of them, thick core! If the fan is working you should be able to hear it. Sounds like a jet getting ready to take off on you! It won't crank up until it gets pretty hot though, I forget what the temp is supposed to be.