Is My Heater Core Bad?

So it’s pretty cold outside now huh, and the heater in your car is not as hot as it should be…or not hot at all.  I am starting to get tons of emails pouring in about this topic, it’s a “hot topic” right now.

The heater core is like a small radiator located in your dashboard, on the passenger side behind the glove box area.  There are two smaller sized water hoses that you can see under the hood on the passenger side of the vehicle going to the 2 metal tubes on the heater core which you should be able to see at the firewall of the vehicle. You will not be able to see the rest of the heater core since it is inside the dash.

When the engine reaches its operating temperature (around 210 degrees) both of those smaller water hoses under the hood should be HOT. If they are not, then check the level of antifreeze  inside the radiator, the heater needs hot coolant in order to produce the hot air.  Low or no coolant in the radiator is the first indicator that there is a leak somewhere in the cooling system and it needs to be repaired.

If you are experiencing an overheating problem as well, then you might have a bad thermostat which is not allowing the hot coolant to circulate in the engine and heater core. If there is not a coolant leak, the radiator is full and no overheating….I would guess and replace the thermostat anyway, because it’s a cheap and easy guess.  Make sure to use the proper temperature thermostat, which is usually 195 degrees Fahrenheit.

If those small heater hoses ARE hot, but you still do not have any hot air blowing out of the vents, then you might either have a heater core that is stopped up with rust and gunk and you need to visit your local auto parts store for a heater core flush kit.

Or, you might have a problem in the dashboard that is not selecting the heater selection.  Most newer cars use an electric motor to divert the air from the blower motor inside the dash to either the heater core, or the A/C evaporator depending on which selection you are using…A/C or heater.

Since the hoses under the hood are hot, and the system is full of coolant then your problem is probably the electric diverter door not moving to the heat selection or the dash control is not sending the signal to move the door to heat selection.

In some cases the heater core will leak coolant, and usually does this inside the vehicle on the passenger floor board area under the dashboard under your feet. Feel the carpets for a slick and oily feeling on your hands, that is what antifreeze feels like. Sometimes your windows will fog up as well when you use the A/C or heater setting, which is another sign of a leaking heater core.

If you are on a tight budget, you can buy a heater core bypass nipple from your local auto parts store and cut the two heater hoses under the hood and hook them together to by-pass the leaking heater core. Of course if you do this you will not have any hot air inside the car.  I have not had much…if any luck using a sealer to seal up a leaking heater core, I know you are asking yourself about it so there.

Here is a pretty helpful video I found about the subject, so take a minute and watch it.

Please share this with your friends,
Austin C. Davis