Blown Head Gasket: Signs, Causes, and What to Do Next

When your engine starts acting up—overheating, losing power, or puffing white smoke from the exhaust—you might be dealing with a blown head gasket, a failed seal between the engine block and cylinder head that lets coolant, oil, and combustion gases mix where they shouldn't. Also known as a head gasket failure, this isn’t just a minor repair—it’s one of the most expensive engine problems you can face if ignored.

A blown head gasket, a failed seal between the engine block and cylinder head that lets coolant, oil, and combustion gases mix where they shouldn't. Also known as head gasket failure, this isn’t just a minor repair—it’s one of the most expensive engine problems you can face if ignored.

Most head gaskets fail because the engine overheated. That could be from a broken radiator, a bad thermostat, or even just forgetting to check coolant levels. Once the metal expands from heat, the gasket can’t hold its shape. Coolant leaks into the oil, turning it milky. Combustion gases bubble into the cooling system, making your coolant reservoir bubble like a soda bottle. And if the leak is bad enough, you’ll start losing power because the cylinders can’t hold pressure. These aren’t guesses—they’re the same symptoms mechanics see every day in UK garages.

It’s not just about the gasket itself. A blown head gasket often means other parts are already worn. The engine overheating, a condition where the engine temperature rises beyond safe limits, often due to coolant loss, thermostat failure, or radiator blockage that caused the gasket to fail may have already damaged the cylinder head or warped the block. If you’ve been ignoring a slow coolant leak or a strange smell from the vents, you’re not just delaying a repair—you’re making it worse. And if you keep driving, you risk total engine failure, which can cost more than the value of the car.

Some drivers think a head gasket sealer will fix it. Sometimes it buys a few weeks, but it’s not a real fix. The only reliable solution is replacing the gasket—and often the cylinder head too. That’s why knowing the early signs matters. White smoke from the tailpipe? Milky oil? Bubbles in the coolant tank? These aren’t myths. They’re red flags that show up in nearly every case. If your car has over 80,000 miles and you’ve never replaced the timing belt or checked the cooling system, you’re playing Russian roulette with your engine.

You’ll find real-world advice here—not theory. Posts cover how to test for compression loss, what coolant tests actually tell you, and why some mechanics skip the pressure test and go straight to a block test. You’ll see how a simple coolant flush can delay failure, and why skipping an oil change after a suspected leak can turn a £500 repair into a £3,000 rebuild. This isn’t about scare tactics. It’s about giving you the facts so you don’t end up stranded with a dead engine and no cash to fix it.