Cars Overheating

Typical symptoms of a bad heater core are no heat, or leaking antifreeze into the cabin at your feet. You could also see the vehicle overheating or running hot.

Hi Fred.

I'm not totally sure I understand your question, but I'll take a shot. Are you saying that the engine fan stays on all the time for your car, keeping the radiator cool, and so you're not able to get any heat in the cabin air? Or possibly that the cabin fan is on all the time and you can't get any heat because it's keeping the radiator cool.

unless there is something very odd about your car (or you're living at the south pole), your engine coolant will be plenty warm within a few minutes of starting. If you are doubtful, drive the car for 5 to 10 minutes, stop, turn off the motor, pop the hood, and carefully move your hand close to the radiator. The blower fan helps transfer heat, but that's to move the coolant temp down probably into the 150-200F range.

if you're not getting any cabin heat, I'd have stronger suspicion about the heater core for your air system. In the majority of vehicles, there is a loop of coolant that comes off the back of the engine block, through the fire wall, and up to a U-Bend of pipe. When the heater is off, the coolant is just re-directed back to the engine. As you turn the knob or lever for cabin heat, it'll turn a switching valve to shunt the hot coolant into a heat exchanger/mini-radiator that the cabin air blows past. This system being a mini-radiator is why highways with long uphill grades will advise motorists to turn on their heater full heat, highest fan, when climbing in the summer. it's an additional way to keep the engine from overheating, even if it sucks for people in the vehicle.

Depending on the car, it can be either easy or really involved diagnosing or repairing the heat exchanger. if you go this route, you'll want to make sure that the coolant is circulated through the core thoroughly and that the coolant-system is de-bubbled.

Good Luck!
D

The cabin heater consists of a heater core and fan. there are two hoses attached to the core, running to and from the engine coolant radiator. One of the hoses has tap or valve to regulate the hot water flow, it is either stuck open or the control cable is broken.

It dosen't happen often, but the air intake side of the core can become obstructed with leaves etc. If that is the case, the only way I know of to fix it is to remove the core & clean it. You did check the heater control valve to make sure it is allowing proper coolant flow through the core, right? Did you run it after refilling the system with the cap off and the heater on high to purge any air in there?

If the water pump was bad you should hear it or if the bearings were bad, then the serpentine belt would likely fall off. run the car until hot and open the cap for the radiator. If there is pressure then the pump is working. And running without a thermostat just keeps a constant flow iwth no engine temperature regulation. I would put a thermostat in and see how the heater works after that.