I have a 2002 4door 4wd with a very strange heat problem. The motor warms to normal operating temp, the heater blower works on all 4 speeds, but at idle there is no heat. If I rev the engine or drive it there is plenty of hot air coming out of the vents. When I stop at a light and let it idle there is no heat again. Does this indicate a partially clogged heater core or a bad water pump or slipping belts? I have not noticed any leaks and the fluids are all topped up.

 

I would say that it is time to flush the core. Once you are done with that, make double sure that you get all of the air out of the system.

 

Also, check your coolant level to make sure you are not low.

 

whats the best way to get the air out of the system?

 

run the engine with the rad cap off about 1500-2000 rpm with a garden hose trickeling over the thermostat housing. Do this till the water is moving good through the rad. It should get the air out.

 

What does trickling water over the thermostat housing do for you? Do you do this with the thermostat housing off as well? I have never used anything remotely close to this method to get air out of a cooling system and have not had any real problems in doing so.

I have always just jacked up the front passenger corner of the truck a bit higher than the driver corner and ran the engine up to operating temperature, then allowed it to cool. Do this a few times and all of the air should be out.