1999 no heat till driving

blower works how come no heat while at idle?

No heat at idle usually indicates low coolant

i already topped off coolant

Did you make sure to bleed all the air out of the cooling system after topped off the radiator?

Air block in the system or maybe a water pump going out.

It’s been my experience that when a water pump goes out it leaks.

Your experience hasn’t included all modes of water pump failure.
They can fail without creating a leak.


No heat could also be a stuck open thermostat. The radiator is removing more heat that the engine is generating at idle, and the thermostat, which is supposed to regulate the temperature of the engine is not doing it at all. The engine is too cool, costing you fuel and heat for the heater.

There’s probably air in the cooling system and when the water pump slows down it collects in the heater core.

To purge all the air out of the cooling system, get the engine up to operating temperature. With the engine idling, slightly loosen the upper radiator hose clamp. Take a small flat bladed screwdriver and insert it between the upper radiator hose and the radiator hose neck. Allow the engine to idle until all the air is purged from the cooling system. Remove the screwdriver and retighten the hose clamp.


I concurr!

Bladecutter, just how does a pump fail, does the impeller wear down? I don’t think so.

just how does a pump fail, does the impeller wear down? I don’t think so.

You have not looked inside a newer plastic impeller water pump.

Joe, you are right, I have never saeen a water pump with a plastic impeller. What kind of a “cheepo” car has one?

Cast impellars can also erode, affecting the ability of the pump to move fluid at idle.

I’d try the T-stat first, coupled with a good air purging.

The function of the T-stat is not to allow the engine to cool, but rather to allow it to heat up. If the engine didn’t need to get to operating temp it would not need a T-stat at all! My money is on the T-stat.