My 1998 Blazer is doing something strange. While I am driving the heat is perfect but If Im idling in my driveway or parking lot the heat gets cold. I have plenty of antifreeze so Im stumped.

 

have any of your cooling system replaced/flushed lately? if so it's possible you have air in the system put front right tire on a ramp and let it idle to cycle a few times to bleed the air out.

 

Are you pulling my leg? I told my mechanic buddy what you mentioned to do and he laughed at me.

 

So what does your mechanic buddy say the problem is?

 

If your mechanic buddy hasn't heard of that process for getting air out of a closed cooling system id be very leery of trusting him to work on my vehicle it's a very basic fundamental of newer vehicles (my daughter learned it in 10th grade auto shop class)

 

The confusion could come from the words you used Outsydr. "Have you had your cooling system replaced/flushed" seems to ask if the entire cooling system has been replaced. I am sure you meant have you replaced the coolant and flushed the cooling system.

As far as the problem, I too would recommend a flush of the heater core. While you are driving down the road, the engine RPM is higher. This can allow for more heat capacity flowing through the core and if restricted can cause a lapse in heat output while idling.

 

What I meant was has any part of the system (ie: water pump, thermostat, radiator etc.) been replaced or flushed lately, so if my wording was confusing then my bad, I apologize for the misunderstanding.

 

I did not mean to insult you. I tried what you said and it seems better. Please accept my sincere apology.

 

Some times you have to do it a cpl times and be sure the radiator cap is off. You also could have a bad radiator cap that will not hold pressure at an idle you can have it checked at any parts house