A classic sign of a heater core problem is when the inside of the vehicle’s windshield persistently keeps misting. Warm coolant is leaking out of the core into the vents and then condensing against the cooler surface of the windshield. The automatic response is to turn up the blowers to try and clear the mist, but this only compounds the problem.
The solution is usually to remove and either repair or replace the heater core. However, this is a particularly time-consuming task, which on older vehicles is often not cost-effective. An alternative solution is to treat the cooling system with a total coolant leak repair additive. These are designed to flow throughout the cooling system, including through the heater core, to make a quick and low-cost repair. Look for a ceramic-based coolant-friendly product, ideally one that conforms to ASTM D-3147.
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