Why is my car overheating?

Overheating means the cooling system can't dump heat fast enough — the cause is almost always low coolant (leak somewhere), a stuck-closed thermostat, a failed water pump, or a fan that isn't kicking on. Pull over the moment the gauge climbs into the red — driving an overheating engine for even a few minutes can warp the head and turn a $50 thermostat into a $4,000 head-gasket job.

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