Odd Heating Problem
 

I have an '04 Silverado with a 4.8 in it. Have an odd heating problem.

The heat coming out of the vents is scalding hot, as if the truck is cooling solely through the heater core. The heater hoses get very hot. The rad has some (not much) heat to it. The top rad hose gets hot, as one would expect, but the bottom rad hose stays cool. I can't really feel circulation in the hoses, but there is some circulation in the overflow tank.

The temperature gauge reads normal, just under 100 degrees, and there are no codes. Hoses are clear of blockage. There is no apparent blockage in the engine at the hose connections. Belt is good and the water pump moves freely.

I've replaced the thermostat and the radiator with no improvement.

Any help, ideas, or even wild guesses would be appreciated.

The heater core is fed from the absolutest hottest part of the engine so it should be HOT.

Now, if the temp won't come down with the temp control, there must be a problem with the temp door or actuator. If you are saying that you want 'cool' air from the vents, then the mode door is hanging, for whatever the reason.

Allan

I've had the truck for about three years and the air from the vents has never been this hot before, Allan.

The temp controls are working properly.

how did you verify the temp blend door is moving?

When I turn the temp down, the air gets cooler.

Living in a cold climate though, it is set to the hottest setting in the winter for most of my daily driving. That's why I noticed the air was so hot.

I've compared it to another 4.8 and a 5.3 in the same weather, same run time, etc.. It's far hotter.

the blend door may be moving but not to it full range.

you need to watch the door position counts to properly rule it out.

the coolant temp should be cooler on the way out of the rad. the coolant temp should regulate from 80-100' celcius. Seems like that part of the system is working normally.