I just bought an 04 silverado 2500HD it has the 6.0 in it. I have driven it for 2 weeks and today when I went to drive it I had no heat and the temp was spiking. But every once and a while it would have heat for a few mins and the temp guage went back down then loose heat again and temp would go back up. I havent seen anything like this with my previous trucks. I was thinking maybe a thermostat but not quite sure because there is a slight whine in the engine so maybe water pump? Any help would be greatly appreciated

Sounds like the water pump may be failing. Look for a small amount of coolant (weep hole) gathering at the bottom of the water pump. With that said, it could also be other things, like a sticky thermostat. The big issue is not to drive the truck while overheating. The damage that can be caused is very expensive to repair.

It hasnt overheated just running higher than normal. Its my only vehicle at the moment so i have to drive it. I figured id start with the thermostat first seeing how its cheap and easy to fix. ill look into it more tomorrow but I appreciate the help.

sounds more like the pump, if it was the thermostat you wouldnt lose heat. and if its making noise its probably time for a belt. its a good time to look over the truck to see if the previous owner did any maintanace, most people only change the oil. it probably needs coolant flushed, diffs changed, trans, check the hoses, etc... if its got over 100k i would put some plugs in it too.

It did end up being the water pump. I put in a new thermostat and of course antifreeze. I plan on doing a tune up come spring on it just dont have time or money atm but thankyou for the help!!

thanks for posting the fix