Rick's Free Auto Repair Advice

Symptoms of failing heater core

How to diagnose a failing heater core

A failing heater core can leak engine coolant into the passenger compartment or fail to heat the cabin. The heater core in your car or truck receives hot coolant from the engine. The coolant flows through small tubes while the car’s blower motor passes cabin air across the heater core tubes and fins to warm the cabin air.

What causes a failing heater core? See this post

Failing heater core failure symptom #1 No heat

Clogged passages in the heater core reduce its ability to transfer heat to the cabin. Heater core passages clog due to corrosion in the vehicle’s cooling system.

How to diagnose a no heat condition

Locate the hoses running from the engine to the heater core. Those will be located on the firewall under the hood. With the engine up to full operating temperature and the blower motor set on high, touch each hose and compare the temperature of the hoses. Both hoses should be close to the same temperature. If one hose is hot and the other is cold, the heater core is clogged and the engine coolant is not circulating through the tubes.

Failing heater core symptom #3 Oily fog on windshield

When a heater core leaks, hot coolant seeps out and is vaporized by the air flowing through the heater box. If the vehicle’s heater is set to the DEFROST mode, the saturated air will blow onto the windshield. There, the coolant laden air will condense to form an oily fog. If you wipe the windshield and it streaks and smears, that’s a sign of a leaking heater core.

oily film on windshield, heater core leaking

Oily film on windshield

Failing heater core symptom #3 Cabin air smells sweet like fruit

When engine coolant vaporizes, it gives off a sweet fruity-like smell. So a leaking heater core will make your car smell like melons or fruit.

Failing heater core symptom #4 puddles under your car

When a heater core leak is large enough, the coolant can flow out through the AC condensate drain and deposit onto the ground. The AC drain tube is usually located on the passenger side of the vehicle near the footwell. If you notice coolant on the ground near the passenger compartment, chances are you’ve got a leaking heater core.

Failing heater core symptom #5 you have to refill the coolant reservoir often

Low coolant can be caused by many things: head gasket damage, leaking water pump, leaking radiator, leaking heater lines, or a leaking heater core. If you have to keep refilling the coolant reservoir in your car or truck, do NOT ignore the problem. It will not fix itself. Have a pressurized cooling system test performed to locate the leak.

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Posted on by Rick Muscoplat

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