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Symptoms of a bad heater core

Symptoms of a bad heater core

The symptoms of a bad heater core may be hard to detect at first but one thing is sure; it won’t fix itself and the symptoms will get progressively worse. Here’s a checklist of what to look for as a sign you’ve got a bad core.

Here are the symptoms of a bad heater core

Your Heat isn’t hot

You turn the temperature dial to its highest setting and you get only luke-warm or cold air. This failure is mostly likely caused by a fully or partially plugged heater core that restricts the flow of coolant and thus the transfer of heat from the hot engine coolant to the air blowing past the core. Sometimes, shops are able to flush a bad heater core and restore its function. But this procedure must be performed at the early stages. If you ignore the low heat condition, the sediment can harden and prove impossible to remove.

Your coolant reservoir is always low, your have no heat and your passenger side carpet is wet

You refill the coolant reservoir under the

is your coolant reservoir always low on coolant

Check coolant level in recervoir

hood and within a few weeks, it’s low on coolant again. The system might be leaking from a radiator or heater hose, but you can usually spot those leaks by looking for drips and wet areas. Or, you may have a head gasket leak that’s allowing coolant into the engine oil or the combustion chamber.

If you’ve checked the hoses and head gasket but are still losing coolant, check for a leaking heater core.

Your windshield is fogging up with an oily film

If your windshield fogs up and the fog feels oily, the fog may actually be misting coolant. Wipe your finger across the fog. If your finger feels oily, the core is leaking and coolant mist is blowing onto your windshield.

You smell a sweet smell when the blower is on

That’s the sure sign of a leaking core. Leaking coolant has a sweet fruity smell when the blower is on. Engine coolant has a sweet fruity smell. If that type of smell gets stronger when you operate the blower, chances are you’ve got a core leak.

Unsure if your coolant is still good? Read this post to learn how to test for failed anti-corrosion additives.

What causes a core to plug or leak?

Coolant neglect is the #1 cause of heater core plugging

All engine coolant contains anti-corrosion additives. When the anti-corrosion additives wear out, metal transfer begins and the cooling system circulates corrosion particles. Those particles clog the small passages in the heater core, preventing heat transfer. Shop can perform a reverse core flush to try and remove the buildup, but if that doesn’t work, the heater core must be replaced.

Wear and corrosion causes leaks

Your car’s heater has hot engine coolant running through it any time your engine is running, or only when you move the temperature dial to HEAT. On vehicles where coolant runs through the heater core whenever the engine is running, the constant flow can slowly wear core showing corrosion out the inside of the small tubes that make up the core. That’s why many carmakers add a flow-restrictor in the heater hose to prevent rapid wear. If you remove the flow-restrictor, you can wear out the small tubes in the heater core.

Heater control valve failure

heater control valve

Cable operated heater control valve

Vehicles that use a heater control valve to regulate the flow rate through the heater core experience a different kind of failure. When the heater control valve is closed, there’s no circulation through the heater core and the coolant sits in place. That’s not a problem if the coolant is in good shape. But if it’s old and worn-out, it’ll corrode the heater core from the inside out.

Wondering if you can fix a leaking heater core with a stop leak product? Read this post for the answer.

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Posted on by Rick Muscoplat

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