Car Overheating: Causes, Risks, and What to Do

Common symptoms

• Temperature gauge climbing above normal or into the red
• Steam from under the hood
• Sweet coolant smell (ethylene glycol) inside or outside the vehicle
• Coolant pooling under the vehicle
• Loss of power or knocking as temperature climbs

Why engines overheat

Overheating comes down to the cooling system failing to move heat away from the engine: low coolant from a leak, a thermostat stuck closed, a failed water pump, a clogged radiator, or a cooling fan that never engages. A slipping or broken belt can disable the pump itself.

It can also be misleading — a bad temperature sensor can report overheating that isn't happening. But until that's verified, treat every high-temperature reading as real.

What to do when it happens

Pull over safely and shut the engine off. Driving an overheating engine, even to the next exit, can warp heads and blow gaskets. Never open a hot radiator cap — the system is pressurized and can scald severely. Let it cool, check the overflow reservoir (visible without opening anything) if safe to do so, and get the vehicle looked at before driving it further.

Professional diagnosis

A shop pressure-tests the cooling system to find leaks, verifies the thermostat opens at the rated temperature, checks fan operation, and tests for combustion gases in the coolant — the telltale sign of a head gasket problem. Overheating diagnosis is one area where guessing is expensive: a gasket job dwarf the cost of a thermostat.

Related diagnostic trouble codes

These codes are stored alongside this symptom often enough to be worth checking — remember that a code identifies a condition, not a failed part.