Show 1523: "Stump the Chumps" Caller Who Had No Heat

Caller had replaced heater hoses, radiator hose, thermostat, water pump, verified the heater control flaps were working, still had no heat. Tom and Ray at the time said it must be air in the cooling system blocking flow to the heater, and suggested to bleed all the air out. That didn’t work. Ray now thinks it may be a problematic head gasket.

That’s possible. Maybe some of the coolant ports may be plugged up. But aren’t there still some relatively simple tests to do before taking on the time and expense of replacing the head gasket?

I had a Jeep come in once for a bad water pump. It came back that afternoon for not enough (no) heat. Imagine my surprise when, after checking all of the obvious, I pulled the new pump and found that the impeller was reversed! I doubt that is the case with this vehicle, given that it had no heat before the pump was replaced, but it would depend on at what point in the process the pump was replaced. In other words, the pump could have been replaced to no effect and then the heater core and still no heat. It could be that the heater core was, in fact, bad but if the pump impeller was reversed there would still be no heat after replacing the bad core. Need more information to determine anything at this point…

I’d be inclined, as a start to figuring out what’s wrong – speaking of the caller’s problem here – to warm the engine up, then get a big bucket and remove the hose going to the heater core and let the coolant flow into the bucket, a couple quarts or so. To see how hot that coolant is. If it is only luke warm, there’s no way there’s going to be any heat in the passenger compartment. And indeed the problem might be the head gasket. But if that coolant in the bucket is very hot, further investigation is required. And a faulty head gasket explanation seems less likely.