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Engine & running faults

Head gasket failure symptoms

Head gasket failure is often suspected and less often confirmed. Testing first matters, because several cheaper faults produce similar symptoms.

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Symptoms drivers describe

  • Coolant disappearing with no visible leak
  • Overheating, particularly under load
  • White smoke from the exhaust once warm
  • Bubbling in the expansion tank
  • Oil looking creamy or mayonnaise-like
  • Poor running or a misfire on one cylinder

Possible causes

  • A previous overheat, often from a cooling fault left too long
  • Coolant loss from an unfound leak
  • A blocked radiator, failed thermostat or fan fault
  • Age and thermal cycling on some known engine designs
  • Cylinder head or block distortion

What you can do

  • Stop driving if it is overheating
  • Do not keep topping the coolant up and carrying on
  • Ask for it to be tested before committing to a strip-down

How we check it in the workshop

We pressure test the cooling system, test for combustion gases in the coolant, check compression and inspect the oil before recommending any dismantling.

Is it safe to keep driving?

Urgent if overheating. Continued running can distort the head and turn a gasket job into an engine job.

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Helpful reading

Go deeper on this fault

Car overheating: what to do and what not to doOverheating damage happens in minutes. What you do in the first two minutes matters more than anything else.Read more

Engine & running faults

Other symptoms in this group

Car stuck in limp modeLimp mode is a protection strategy, not a fault in itself. The control unit has seen a reading it does not trust and has reduced power to keep things safe.Read more White smoke from the exhaustColour, smell and whether the smoke clears once warm are what separate normal condensation from a coolant or fuelling problem.Read more Blue smoke from the exhaustBlue smoke points at oil reaching the combustion chamber or exhaust. When it appears — start-up, overrun or under boost — narrows the cause.Read more Black smoke from a diesel exhaustBlack smoke is unburnt fuel. On a modern diesel with a DPF it usually also means extra soot heading into the filter.Read more Car losing power when acceleratingLoss of power is either a fuelling, air or protection issue. Live data under load is what separates them rather than guesswork.Read more Car cutting out while drivingIntermittent cut-outs are among the most important faults to record properly, because the evidence disappears the moment the engine restarts.Read more

Want this looked at properly?

Send us your registration and describe the symptoms — we will tell you what the next step is.

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