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How To Fix Your Car's Heater

Here's what to do if your vehicle is struggling to turn up the heat.

Cropped Image Of Man Driving Car During Winter
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When winter arrives, the last thing you want breaking down is your car's heater because not only is a frosty car inconvenient—it's also dangerous.

A broken heater in the winter is far worse than malfunctioning A/C in the summer. This genuinely becomes a safety hazard because heat is needed to remove ice and fog build-up on your windshield—not to mention that extreme cold for extended periods is extremely dangerous.

So what happens if your car heater zonks out in mid-January? Here are a few things to try before heading to the mechanic.

How Your Heater Works

car air conditioner control unit
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A car’s cabin will heat up as the engine’s coolant heats up. The coolant absorbs the heat from the engine, causing it to become hot. This coolant is then routed through a “mini” radiator called a heater core. This heater core then passes the hot air it generates into the vehicle with a blower fan.

Many different things can go wrong here causing the whole system to work poorly or not at all. Checking to make sure the engine warms up properly is number one on the list. When driving, an engine typically takes about 5-10 minutes to reach its proper temperature.

Check the Thermostat

To help engines warm up fast and then keep it at a steady temperature, manufacturers use a thermostat to control the flow of coolant. If the engine is cold, the thermostat will restrict the flow of coolant into the engine, allowing it to warm up quickly. Once it’s reached the proper temperature, a valve in the thermostat opens and allows coolant to flow through the engine.

Thermostats are a common wear item, and typically break open, so it’s always allowing coolant to flow through the engine. This will make it incredibly difficult for the engine to heat up in cold temperatures since it’s constantly being cooled. If the thermostat breaks closed, then you’ll have overheating problems, but they’re not designed to break that way.

Other Heating Woes

Head restraint, Vehicle, Car, Mode of transport, Driving, Vehicle door, Family car, Auto part, Passenger, Car seat cover,
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Replacing a thermostat is a relatively easy DIY project on some cars but can be difficult on others. If the car does get up to temperature as it should, there’s probably something else that has gone bad.

Buildup of grime is fairly common in coolant systems, so there could be a restriction somewhere. If the holdup is by the heater core, then that’s one reason why hot air isn’t blowing. Fixing this can be as simple as a fluid flush. You’ll want to flush it several times with water to get all the sediment and build-up out of the heater core or blockage area.

A different reason for the heat to not work would be a lack of coolant going through the engine. This will cause plenty of other issues, but there won’t be enough coolant to sufficiently warmup that heater core as well. Coolant doesn’t just disappear though, so there’s a leak in the system somewhere that you want to find sooner rather than later.

One of the more obvious problems would involve the blower fan not pushing any air out of the vents. If the fan has broken, then there certainly won’t be any warm air from the heater core coming your way.

It’s not always easy to diagnose heater problems. Sometimes it can cost up to four figures if you have a bum heater core, other times it’s as easy as a broken switch or dial on your dash. Whatever it may be, consulting forums specific to your car and speaking with a mechanic should help set you on the path of being warm and happy again.

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