Intermittent Heat - 2002 Chevy Blazer

[ThrasherFan]

Is there any logical reason the heater in my Blazer would only blow hot air while my foot is on the accelerator? While I'm driving, it seems fine, but when I'm idling at a light, the air blows cold. Or, maybe it's just intermittent and coincidental regarding the accelerator. Any ideas on what this might be and how to fix it?

[Mr. Dummas]

Low coolant level. Let the engine cool, remove radiator cap, start engine, and then check the fluid level and add if need be.

[ThrasherFan]

Thanks for your help!

[Civicminded]

I would check you radiator filler neck, if it is a rusty mud color and sludgy you have the infamous gm dexcool problem. It causes all kinds of problems with the cooling system including intemittant heat. If this is the case I would backflush the heater core, flush the entire system and use traditional coolant. Do you ever hear gurgling sounds on the right side of the dash when you raise engine rpm? If you do the coolant is low and or the heater core is plugged.
Dexcool is junk imho.

[Mike.B]

Dodge Caravans had a similar problem, but it was mostly due to heater core being up so much higher than the engine, that under normal idle, water pump just didn't push enough coolant through the heater core. As soon as you increased the rpm of the engine, it obviously pushed more & harder to allow coolant to run through core better. Had one that was worse then most, disconnected hoses at core near firewall, bought one of those cheap drill operated pumps, attached the hose to one of the core fittings, other into a pail of C.L.R., and circulated it through. Let the CLR sit in core overnight, circulated a few more times next day. Re-attached hoses, added coolant, bled system, (with heater on ) and it was 50%-75% better, and no big bill for core replacement.