Over heating

I have a 2002 impala with a 3.4 lt

the temp runs fine until i turn on the heater then the the car tends to over heat but i only get cold air from the fan.

Sounds like you have low coolant level, try refilling with 50-50 antifreeze. If that fixes it keep an eye on the level, you could have a leak.

That would be my first place to look. Oddly, it should produce hot air except at idle …but that depends on how far low it is. One would reason that you probably use the heater core as the bypass hose (most cars) and that the heater would only act as an additional radiator. It may not be the case with your installation.

I flushed the radiator,replaced the radiator cap,replaced the thermostat,and replaced the water pump and did a presure test and still having the same problem.

Try this.

Get the engine up to operating temperature. With the engine idling loosen the upper radiator hose clamp. Take a small flat bladed screwdriver and slip it between the upper radiator hose and the radiator hose neck. Allow the engine to continue to idle until a steady stream of coolant comes out of the radiator hose. Remove the screwdriver and retighten the hose clamp.


Can you give us the event train? Have you switched on the heater …experienced the increase in temp …shut it down …restarted …repeated? I somehow can’t see this not burping itself. Some are more difficult than others.

Get a longer piece of heater hose. Break it mid-span (by a mender and clamps before hand). With the engine COLD, fill the engine with coolant mix through the hose. Eventually the coolant will pour out of the other end of the hose. You’ll be holding this above the highest level that the coolant will ever see while sealed …well above the heater core …well above the intake …well above the radiator.

Mate, clamp, start. This is somewhat draconian, but you need to eliminate any air that may be trapped in the engine. This is the only way I can describe that will 100% assure that you get it correct.

Good luck.