Here’s Why Your Car Has No Heat

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The first cold days are here and now your car has no heat. We run down the reasons why so you can feel warm and toasty again.

Winter is coming. It’s time to check that heating system to be sure you have no surprises. Turn that temp knob to fully red, or your digital temperature setting to well above the outside temp and crank the fan. If the fan works, we move on. If not, you need the fan serviced. Fan works, but still no heat? Here’s what to check yourself, and what to be prepared for if you need service.

Step One – Start With A Cold Engine – Check The Coolant

WARNING – If you do this first step with an engine that is not cold you are going to be injured. So be sure the car is stone cold before you begin. Now grab some safety glasses and wear them. Next, pop the hood and find your coolant reservoir. It will be a translucent white tank with a dip hose leading to it. Unless you have a BMW. If you have a BMW it will look like half of a cartoon bomb (really) and not be see-through. Use your manual to find the tank if you are not 100% sure. Observe the level of coolant. It will either be green or pinkish red. If there is none in there, you may have found the problem. The tank is marked with a high and low point. Note where it is when the vehicle is cold (usually low). Also, visually observe the level of the coolant when the car is warmed up from having been driven. The coolant should be higher in the reservoir when the car is at running temperature. Your car’s heating and cooling system uses the coolant to move heat from the engine into your car’s heater core. That’s small radiator sort of thingy hidden behind the engine. A fan blows over this heater core and the warmed air enters the cabin. If there is no coolant it can’t work.

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If you have no coolant in your reservoir the next step is to open the radiator cap. Again – ONLY WHEN THE CAR IS STONE COLD. Touch the cap gently to be sure you are right that the car is cold. If it is, open it up and carefully set it aside so it doesn’t fall down into the engine. Note what you see. If there is no coolant at the top, you have made some ground on the diagnosis. If it is there, you will be calling a mechanic, but at least you can tell her the status of the fan and the status of the coolant! You are now an educated customer.

 

If there is no coolant in the radiator, use your manual to find out what type it uses and then head over to a local car parts store and buy it and fill it up. You may be in luck, or you may have a leak that requires a trip to a mechanic.

Heater Core Issues

The heater core in your vehicle is a simple device, but it can run into a few common problems. The first is that it can become air-bound or be blocked with air. Filling up your coolant may have helped. Some vehicles are more prone to this issue than others. If this is your problem, you are a lucky duck. Either you or your trusted mechanic will solve it and your wallet will remain fat.

Next up is a problem with the heater core. It could be gunked up. It may have a leak, which you would likely have found out about when your car overheated, or if you have a wet floor in the front. There is also a door that opens and closes to allow the warmed air into the cabin. All of these are mechanic-diagnosed issues. Replacing a heater core will require the part, plus labor. Not cheap, but you won’t have to get a second mortgage to solve it either.

Thermostat Issues

Another likely cause of a car that runs OK, but has no heat is a stuck thermostat. A vehicle thermostat regulates the coolant temperature in the engine. If it is stuck, it may be allowing the coolant to always be run through the radiator, which keeps it too cool to allow for heat in the cabin but will still allow the vehicle to run. John Paul, The Car Doctor, told us, “The most common issue with poor heat in cold weather is due to a malfunctioning engine thermostat. My advice is whenever a car overheats, hose leaks, radiator leaks or if the car has suffered from a simple lack of maintenance—replace the thermostat.” A stuck thermostat is not a big job for a mechanic and the part is relatively inexpensive. The job is mostly labor. You can often tell if you have this issue by observing your car’s temperature gauge (if it has one). If it always stays near the cold side, the engine is not warming up properly. Likely due to a stuck thermostat.

Bigger Issues

Aside from these relatively simple things, your car may have a belt or belt tensioner issue or a water pump that is worn out or not working for some reason. A water pump is a more expensive fix and if your car is older, don’t be surprised if the mechanic suggests some other maintenance items since getting at it may require some disassembly of the engine. Fingers crossed this is not your issue, but if it is, it may be due to a lack of prior maintenance, or just bad luck.

Give your mechanic a call after you have done the coolant check and observed your car’s temperature gauge when it should be warm. Now that you know the basics, you will be able to have a conversation with the mechanic and feel better about the resulting diagnosis and repair bill.

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John Goreham

John Goreham

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