Blown Head Gasket: Symptoms, Cost, and When Selling Beats Repairing

Blown head gasket symptoms are unmistakable once you know them. The gasket seals the joint between the engine block and the cylinder head: it separates the combustion chambers, the oil galleries and the coolant passages. When it fails, those three worlds mix — and the engine destroys itself within a few dozen kilometres.

Almost always, the cause is the same: an overheat that was allowed to continue.

The five signs

1. Thick, persistent white smoke from the exhaust that does not clear once the engine is warm, with a sweetish smell. That is coolant burning.
2. Beige foam under the oil cap or on the dipstick: water has mixed with the oil.
3. A falling coolant level with no visible leak under the car.
4. Bubbles in the expansion tank with the engine running, or coolant overflowing: combustion gases are entering the system.
5. Rapid, repeated overheating, often with power loss and a rough idle.

Any one of these justifies immediate diagnosis. Two together, stop driving.

Confirm before dismantling

A good workshop does not dismantle to find out. It confirms first with a compression test cylinder by cylinder, and a chemical gas test on the expansion tank, which detects combustion gases in the coolant. Both cost little and avoid a pointless strip-down.

If you are offered a head rebuild with no prior testing, ask why.

What the repair really involves

The gasket itself is cheap. What costs is everything around it:

• Labour — removing the cylinder head takes time.
• Skimming or replacing the head if heat has warped it, which is common after prolonged overheating.
• Checking the block, which may also have suffered.
• Ancillary parts: timing belt or chain, hoses, thermostat, and usually the water pump since everything is already apart.
• The original cause — there is no point repairing the gasket without repairing the cooling system that killed it. See our guide to the radiator and coolant.

Repair or sell: the honest calculation

What the car that usually has this problem is worth

This calculation turns entirely on residual value, and the market numbers make it plain. On MotoNaMarket the median is 3 300 000 FCFA for a Toyota Yaris (27 listings, median year 2005) and 4 000 000 FCFA for a Corolla (47 listings, median year 2006). On a car worth that, a badly quoted head job swallows a major share of the resale price: insist on a written quote and a confirmed diagnosis before authorising any strip-down.

Figures taken on 26 August 2026 from 347 active MotoNaMarket listings.

Compare three figures: the full quote, the vehicle's value repaired, and its value as it stands.

• On a high-demand model in otherwise good condition with available parts — Corolla, RAV4, Hilux — repair often makes sense.
• On an older, generally worn vehicle, or one whose parts must be ordered abroad, the quote frequently exceeds what the repaired car will be worth.

Place those values with the price estimator and the price guides by model. If you decide to sell as it stands, say so plainly: a hidden defect discovered after the sale exposes you, and a car advertised as needing engine work finds its buyer at the right price. Auctions suit this case well, where the market prices it better than negotiation.

Preventing it is simple

You do not prevent a head gasket directly: you prevent the overheating that kills it. Check hoses, cap, fan and level at every oil change, never run on tap water long-term, and stop at the first rise of the needle. The difference between stopping immediately and "doing the last twenty kilometres" is exactly the difference between a hose and an engine.

Compare parts on the auto parts marketplace, get a written quote — find a mechanic — and when buying used apply the 12-point checklist, price the repair with the price estimator and browse cars for sale.

The engine fluid specifications that protect these components are documented by the American Petroleum Institute.