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Eric, Master Technician/shop foreman
Category: Chevy
Satisfied Customers: 846
Experience:  ASE Master Technician, 25 years experience, Over400 General Motors certifications
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2000 GMC: 4.3 liter engine...cooling system..heater core../fill kit

Customer Question

No heat from heater, 2000 GMC Jimmy SLT - not Envoy. 4.3 liter engine. Back flushed cooling system through heater core using prestone flush/fill kit, new thermostat too. Temp knob on dash seems to do activate something (when zone seletor sw. is in defrost and fan sw on high, the air movement is high when temp knob is on hot and when i move the temp knob to cold - air movement is considerably less.) does this mean the blend door actuator is working? Why still no heat?
Submitted: 7 years ago.
Category: Chevy
Expert:  Eric replied 7 years ago.
Hi, what type of control head does it have? dual zone, with 2 sliders for temp or one single temp slider or knob? Also, even though you flushed the core, are both heater hoses going into firewall getting hot? Is it manual controls or automatic? Let me know and i will try to help you out. Thanks,Eric
Customer: replied 7 years ago.
The 2000 Jimmy (small one like an s-10 pickup) has a 3 rotating knob setup - 4 pos fan, potentiometer temp, and vaccumn zone selector ie; max AC/AC/dash only/dash&floor/floor only/defrost&floor/def only). I don't know the difference between manual and automatic - but i need to rotate the center temp knob in order to change the temperature. It's also difficult to tell if both hoses are hot, they feel the same but the large rad hoses feel hotter.
Expert:  Eric replied 7 years ago.
So it blows no heat at all? or just a little? The hoses should be basically too hot to touch for very long with the engine hot. Have you gotten all the air bled from the system? Let me check on a couple things and i will post back shortly. Thanks,Eric
Customer: replied 7 years ago.
When say on windsheild defrost and temp control on full hot, it almost feels like it's on AC - does not blow any hot air whatsoever. All air has been bled and waterpump seems to be working. Again - Temp knob on dash seems to activate something (when zone seletor sw. is in defrost and fan sw on high, the air movement on top of dash is significant, but when I turn the temp knob to cold the air movement changes to considerably less.)
Customer: replied 7 years ago.

ADD: Is there a control valve (controlling water flow to heater core) on a 2000 Jimmy? If so, where is it located? Maybe it is clogged or not functional.

Customer: replied 7 years ago.
Well it looks as if the heater core was possibly clogged - so far. When i used the flush fill kit originally, I had also used my hose pinching pliers to make certain that water flow was forced to go through the heater core, so i'm at a loss still, but i'm forward flushing it at the moment and got a buch of corrosion to pass.
Customer: replied 7 years ago.
Looks like I have fixed the problem. I completely isolated the heater core and flushed it forward and backwards.
Expert:  Eric replied 7 years ago.

Yes, sounds like your on the right track. Its a common problem with the Jimmy/Blazer.

Flush it out good, sometimes you may even need to drive it again, then flush it again. Good luck, Thanks,Eric