Car Overheating or Losing Coolant? Signs of a Blown Head Gasket

If your car is overheating right now

Pull over as soon as it is safe and switch the engine off. Do not open the coolant cap while the engine is hot — the system is under pressure and the coolant can scald. Driving an overheating engine is one of the quickest ways to cause serious damage, including a blown head gasket or a warped cylinder head, so it is far cheaper to stop early than to push on home.

Common causes of overheating

Most overheating is caused by losing coolant, and most coolant loss is from a simple leak: a split hose, a leaking radiator, a failing water pump or a faulty expansion tank cap. A stuck thermostat or a broken radiator fan can also cause it — a fan fault often shows up as overheating in traffic but not at speed. These are all much cheaper to fix than a head gasket, which is why it is worth a proper diagnosis before assuming the worst.

Signs of a blown head gasket

Coolant going down with no visible leak anywhere.

Thick white smoke from the exhaust with a sweet smell, especially once the engine is warm.

Bubbles in the coolant expansion tank with the engine running, or the top hose going rock hard.

Repeated overheating, or the heater blowing cold as the coolant level drops.

A milky, mayonnaise-like sludge under the oil filler cap. Be careful with this one on its own — cars used only for short trips can get condensation there without any gasket fault.

How we confirm it

We pressure-test the cooling system to find any external leaks and test the coolant for exhaust gases, which only get in if combustion gas is leaking past the gasket. We read the fault codes and check the thermostat, fan and water pump too. That tells us whether it really is the head gasket or something simpler, and we give you a written quote either way.

If the car is overheating, do not drive it far. Call us on 0121 476 2287 — we are on Bristol Road South in Northfield, close to Selly Oak, Kings Norton and Longbridge.