5 Fixes for a Broken Car Heater

The Right Way to Fix a Broken Car Heater

The right way to deal with a broken car heater is to start with some basic diagnostics and then fix whatever is wrong.

The exact diagnostic procedure will vary from one vehicle to another, but if your car heater is blowing cold, then a good place to start is with the coolant. If the coolant is low, then there may be air in the heater core, which would explain why your heater isn’t working. Find and fix the leak, fill it up, and that may be the end of it.

If the coolant is full, then a good way to check the operation of a few important components is to grab a non-contact infrared thermometer. That allows you to check whether the coolant is heating up properly, as a stuck thermostat can cause a heater to not function properly.

An infrared thermometer also allows you to check the input and output hoses on the heater core. If the output line is cold, then you might have a plugged heater core or a valve that isn’t opening.

Inside the vehicle, problems like a bad blower motor, heater switch, blend door, or blower motor resistor can cause the heater to not work. If you can identify the specific component that failed, you can replace it, and you’ll have heat again. Otherwise, you have to pay someone to do the diagnostic work for you.

Some problems that keep a car heater from working right are relatively cheap, quick fixes, while others are exceedingly costly. For instance, some heater cores are buried so deep that you have to remove the entire dashboard to get to them. If you’re dealing with that type of situation and money is tight, then you might want to consider a quick fix and a car heater alternative to get you by.

The Quick Fix for a Bad Heater Core

Most car heater problems aren’t really a big deal if you just leave them be until you have the money to fix the failed component, but a leaking heater core is a big exception to that. If your heater doesn’t work because the heater core is leaking, you could end up dealing with a bunch of sticky, smelly antifreeze on the floor of your car, and the engine could even overheat if the coolant level gets too low.

The quick fix for this problem, if you can’t afford the repair bill, is to bypass the heater core. You can do this yourself by cutting the heater hoses where they attach to the heater core and then splicing them together, so long as you make sure to tighten the splice with good worm gear clamps and route the spliced hoses so they don’t rest on a hot surface like an exhaust manifold or fall into the engine belts and pulleys.

If you don’t feel comfortable bypassing your own heater core, a sympathetic mechanic should be able to do the job relatively inexpensively, unless the heater core is exceptionally difficult to access.

Once the heater core is bypassed, you can either tough out the cold or explore some car heater alternatives that might be enough to get you through the winter.

Electric Defroster Replacements

One great way to fog up a windshield is to run the heater, set to defrost, with a leaky heater core. Antifreeze will atomize, spray all over your windshield, and leave a sticky, foggy film that just kind of smears around when you try to wipe it off.

If you’re sure there isn’t any antifreeze in your heater box, and you were lucky enough to not have sprayed antifreeze all over your windshield, then you may find that turning on the A/C with the defrost setting on may defog your windshield just fine. It won’t melt ice on the outside of the windshield like your heater would, but it’s fine in other situations.

The other option, if your heater is busted, is an electric defroster replacement. These devices aren’t meant to warm up the interior of the car at all, so they aren’t any use if you’re in an area where it gets cold enough that you need some heat in your car to survive your morning commute. But if all you’re looking for is something to defog your windows, and the A/C method doesn’t work, then this may be what you’re looking for.

Electric Car Heater Replacements

If you want to stay warm on the road without a functioning car heater, then some type of plug-in car heater is your only real option.

An electric car heater is a poor replacement for a functioning heater core, but it’s better than nothing. This type of 12-volt electric heater typically isn't going to be powerful enough to make it toasty warm in your car like a functioning car heater would, but pointing one in your face may take enough of the edge off to make your commute at least resemble something comfortable.

Another electric car heater option is to run an extension cord out to your car with a space heater that’s safe to use in a confined area like a car and run that before you drive in the morning. You’ll quickly lose heat once you shut it off and start driving, but coupled with a battery-powered heater, you might stay warm enough on a short commute to make it worthwhile.