Hi everyone! Thanks for taking the time to read my post. My question is simple. What is the most likely culprit for the following....

I own a 2001 SC w/5.4 . Never had a heat problem before. Since it has gotten cold this year, the heat output is pretty weak. I noticed too that the engine warms up initially to a normal temp. At that point, I get nice, hot heat. Then the thermostat opens and the engine temp falls to just off the cold mark and remains there no matter how hard I drive the truck. The heat output at this point is weak. It's still warm, but nowhere near what it should (or used to) be. I am thinking coolant mix or worn out thermostat.

Thanks,
Tirant

 

Sounds like your thermostat is sticking in the "open" position. You might want to check you temperature adjustment ****. They have a bad habit of cracking where the **** goes on to the shaft of the rheostat. Just pull it off to check.

 

Sounds like a thermostat sticking open. Change it before it sticks closed. The thermostat is cheapest part of coolant system, but one of the most important parts. Replace it with a fail open 190 deg F thermostat. These will always fail in the open position. It's better for you to be a little cool than it is for the engine to over heat.

Happy Truckin

 

Thanks for the replies. I was leaning towards the thermostat. Never heard of one partially working. Usually they stick one way or the other. I'll give it a try.
Thanks again!

 

Okay, it was -4 to -7 in and around the twin cities this morning. I let the truck run for about 10 minutes (was sitting outside). I then drove it 35 miles to work, it never got into the normal operating temps and i really had not heat either. Does this sound like a thermostat that is stuck open, or shoudl i just try the cardboard in front of the radiator to see if it will heat up?

Thanks!

 

Sounds like you have the same problem I had. As it turned out, my thermostat was stuck open. I replaced it and I get great heat now.