I have a similar problem on a 2001 chevrolet 2 door blazer. I turn the heat all the way on (manual controls) and i get very little heat. With the fan low, i get luke-warm air. With the fan on High (#4) i get COLD air.

I have checked the hoses leading to my heater core. The hose closest to the passenger side is very warm (not scalding), and the other hose is barely warm if not cold. I recently had my heater core flushed by a company. THey installed a plastic "T" in the 'cold' heater core hose and used pulsating air and water to reverse flush the system (to the best of my knowledge). It seemed to help a little, but I still get almost no heat.

The mechanic believes that replacing the thermostat is the next best step. I am not as knowledgable as I'd like to be about this heating system on the truck, but I'm lead to believe it is a clogged heater core. What is the problem with my truck... and how do I go about fixing it? Do I need to replace my heater core (groan)? Thanks for any help!!

Both heater hoses should be almost too hot to hold with bare hands. There might be an air pocket in the cooling system, but more likely it's a restricted heater core. Remove both heater hoses from the engine, stick a garden hose in one of the heater hoses and flush until the water runs clear from the other heater hose. Then stick the garden hose in the other heater hose and repeat. (Flush in both directions) Reconnect the hoses, top off with coolant, bleed air from the system. If still no heat, replace the heater core.