Why Is My Car Overheating? Causes and What to Do

What the temperature gauge is telling you

The temperature gauge on your dashboard shows coolant temperature. On a healthy engine, the needle should settle in the middle of the gauge within a few minutes of driving and stay there. If it climbs towards the red, or if a temperature warning light comes on, your engine is running hotter than it should be.

Modern cars also have a separate coolant level warning that illuminates independently of the temperature gauge. If both warnings appear together — low coolant and high temperature — the engine has likely lost coolant through a leak and is running without adequate protection.

What to do immediately

If the temperature gauge enters the red or a warning light appears, stop driving as soon as it is safe to do so. Turn the engine off. Do not open the bonnet immediately — the cooling system is pressurised and steam can escape suddenly when the bonnet is opened. Wait at least 15 to 20 minutes before checking anything under the bonnet.

Never open the radiator or expansion tank cap on a hot engine. The coolant is under pressure at high temperature and can spray scalding fluid onto your hands and face. Once the engine has cooled for at least 20 minutes, check the coolant level in the expansion tank — not the radiator directly.

Common causes of overheating

Low coolant level is the most frequent cause — usually from a slow leak at a hose, the radiator, the water pump, or the head gasket. A faulty thermostat that is stuck closed will prevent coolant from circulating and cause rapid overheating. A blocked radiator reduces the system's ability to shed heat. A failed water pump stops coolant circulation entirely.

Causes to look for:

• Low coolant — hose, radiator, or water pump leak
• Faulty thermostat stuck in the closed position
• Failed water pump not circulating coolant
• Blocked or damaged radiator
• Head gasket failure allowing combustion gases into the coolant
• Cooling fan not operating at low speeds or in traffic

Head gasket: the expensive outcome of ignoring overheating

A head gasket failure can cause overheating — but overheating can also cause head gasket failure. The two are closely linked. If a car overheats and is driven further in that condition, the cylinder head can warp. A warped head no longer seals correctly against the block, and the head gasket blows.

Signs of a blown head gasket include white sweet-smelling smoke from the exhaust, coolant loss without an obvious external leak, oil and water mixing (visible as a grey or creamy residue under the oil cap), and bubbles in the expansion tank. If you see any of these, stop driving and call us.

Getting it diagnosed in Bromsgrove

We carry out cooling system pressure tests, thermostat checks, and combustion gas tests on coolant to distinguish between a simple hose leak and a head gasket problem before recommending any strip-down work. If you have experienced overheating or your temperature gauge is behaving unusually, call us on 01527 336608 or book online — early diagnosis is always cheaper than the alternative.