Even if you live in Florida, Texas or California, these days you need your car's defroster to work properly to fight those early morning chills, and if you live up north a working heater can be a matter of life or death. Read on and we will cover how your cars heater and engine cooling system work, what the most common causes of it not working, and how to fix it.
The cooling system on modern cars is fairly straightforward. A network of passages carry liquid antifreeze/coolant around the hotter parts of the engine. The coolant is forced around the passages by a water pump. A thermostat prevents the coolant from flowing until the motor gets warm enough. Rubber hoses carry the coolant from the motor to the radiator, and also to the heater core, which is basically a smaller radiator under the dashboard.
The radiator uses the outside air and a fan to cool the fluid in the system, while the heater core uses the heat from the coolant and a fan to warm the air inside the car.
For the cold engine to warm up quickly, it is fitted with a thermostat. When cold the thermostat restricts the flow of coolant to prevents it from entering the radiator. Once the engine is up to temperature the thermostat opens and the coolant flows around the whole system. The thermostat, and clutch or electrically controlled cooling fan work in conjunction to keep the water at the optimum temperature. This is why, once your car warms up, the temperature gauge should remain relatively static.
If the temperature gauge isn't moving much from the lowest reading, or the car runs poorly for more than a few minutes on a cold day, the cooling system may not be working properly. There are a few potential culprits for why your car engine coolant may not be heating up:
Fixes: The only way to fix a faulty thermostat or temperature sender is to replace it. If the coolant is low, or there is an air lock (and also after replacing any faulty parts) you need to fill the system properly. To do this, set the heater controls in the car to maximum heat, remove the radiator cap (or remote mounted coolant pressure cap, sometimes on the overflow tank) and fill to the correct level. Now start the engine without replacing the cap and idle for a few minutes. Watch for the coolant level to drop as the thermostat opens.
Keep topped up to the max level with the engine running. Squeeze the top radiator hose to help air pump around the system (taking care to avoid any moving parts, in particular the radiator fan, which could come on suddenly without warning). Between the engine heat and the water pump, all the air should be forced from the system. Once full and warm, replace the cap and test drive.
A car heater that isn't working could be caused by several simple issues. Either the blower isn't working, in which case you may get warm air but not much of it, or it is blowing air but it may not be very hot. Here is what to check if your heater or defroster isn't working: