I had problems with a similar truck,a 1998 GMC diesel after checking to make sure the control cables were operating the blend door and blowing the mess of the heater core,I replace the thermostats.Still no heat turns out there was a small amount of debris collecting in the fitting for the inlet hose at the thermostat housing after removing it and blowing out the lines the heat was fine.
Try removing the heater hoses from the waterpump and the intake mainfold. Then use a compressor to blow out the gunk in the heater core (place the air hose into the the hose you took off the water pump). This worked for my 2001 jimmy.
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Hi, First check fuses. second, replace thermostat in engine cooling system. Third, If heater fails to produce any heat Flush out heater system and put new 50/50 mix of (ethlineglyco) radiatorfluids.
Probably air locked. check to see if one of the hoses leading into heater is hot. Other cause could be heater solenoid control valve faulty.
Very unlikely that the heater matrix is blocked.
Easiest way to bleed heater is to remove hose's when car is cold and GENTLY flush through with garden hose and push hoses back on when full of water, so you know you have a heater full of fluid.
Hope this helps
I've had this problem. 2000 GMC uses a closed coolant system. Meaning takes and returns coolant from and to the Reserve Bottle and has little air in the engine and heater systems.
If everything appears ok but no heat. "Air Lock" is the most likely cause. (With interior heater set to full heat) Solution; 1. Make sure water pump works. 2. Drain about 1/2 engine coolant into container. 3 Remove both heater hoses from engine side and flush heater core in both directs through heater hoses with garden hose. 4. Reattach heater hoses in correct locations. 4. Refill engine with coolant. 5 Start engine and run for 2 min., use caution when topping up coolant.
6. Most 2000 GMC have twist off caps with plugs located mid way on heater hoses. with engine cold, start engine these caps may be loosened to allow trapped air to escape. Do not attempt with engine hot due to hot coolant injuries. This may take more than one attempt to remove all air from heat system. 7. Lastly most 2000 GMC water pumps have a bleeder plug,( 3/8" square driver plug) located on the water pump. With egine cold this plug should be removed to remove any air. Reinstall plug with thread sealant.
Hope this helps cheers
if you got heat when its running and almost nothing iddling the heater core inside the car has rectriction idle circulation not enough prestone pass thrue the radiator because of scale when our driving way more circulation more prestone go thrue ¸=more heat you need to flush the radiator inside the car normally i put a radiator flush leave it running longer then what they say go for a drive remove the heater core hose be carefull not to break the pipe use garden hose pass hose water pressure o n both side do it a few time each side flush all the prestone add new prestone you shoul have way more heat good luck p.s some shop might tell you change the heater core that perfect but very big money do it right its cheap and gonna work pierre