Blown Head Gasket: Symptoms, Repair Cost, and Whether You Should Fix It

If you've noticed white smoke from the exhaust, the engine running hotter than usual, or a milky, mayonnaise-like residue under the oil cap, you may be dealing with a blown head gasket. It's one of the most common serious engine failures on UK roads, and the symptoms often appear gradually before the fault becomes severe enough to fully confirm. A full head gasket repair typically costs £500 – £2,000 on an average family car, rising to £900–£3,000+ on premium, turbocharged, or larger engines - and if the engine has already overheated badly enough to warp the cylinder head, you may be looking at a full engine rebuild instead.

This guide walks through how to check for the symptoms yourself, what a repair realistically costs, and what your options are if the car isn't worth fixing.
 

What Does a Head Gasket Actually Do?

The head gasket sits between the engine block and the cylinder head, sealing the combustion chambers and keeping oil, coolant, and compression separated from each other. When it fails — "blows" — one or more of those seals breaks down, and oil, coolant, and combustion gases start mixing in ways they shouldn't. Depending on exactly where the gasket has failed, you might see coolant burning in the engine, coolant leaking into the oil, or oil leaking into the coolant. Each produces slightly different symptoms, which is why head gasket failure can look different from car to car.
 

How to Check for a Blown Head Gasket: Symptom Checklist

If you suspect a problem but haven't had it confirmed by a garage yet, these are the four checks worth doing first. You don't need any tools beyond a torch.
 

1. White smoke from the exhaust Look for thick, white smoke that continues once the engine is warmed up - not the thin wisp of condensation you sometimes see on a cold morning that clears within a minute or two. Persistent white smoke, especially with a faintly sweet smell, usually means coolant is leaking into the combustion chamber and burning off as steam.
 

2. Mayonnaise-like residue under the oil cap or on the dipstick Remove the oil filler cap and look at the underside, and check the dipstick. A creamy, frothy, light-brown residue — often described as looking like mayonnaise or the foam on a cappuccino — indicates coolant has mixed into the engine oil. This is one of the clearest single signs of head gasket failure and is usually visible without any special equipment.
 

3. Coolant disappearing with no visible leak If your coolant level keeps dropping but there's no puddle under the car and no obvious external leak, the coolant is likely going somewhere internally - either burning off through the exhaust or mixing into the oil. Keep an eye on both the radiator and the overflow reservoir over a few days.
 

4. Overheating, rough running, or loss of power A failing gasket can affect engine compression and cooling efficiency at the same time, which often shows up as the temperature gauge creeping higher than normal, a rough or uneven idle, misfiring, or a noticeable loss of power under acceleration.

If you're seeing even one or two of these signs, it's worth getting the car checked promptly. If you're seeing several together, treat it as confirmed until a mechanic tells you otherwise, and avoid continuing to drive the car — running an engine with a blown head gasket for too long is what turns a gasket replacement into a full engine rebuild.
 

How Much Does It Cost to Fix a Blown Head Gasket?

The part itself is inexpensive — usually £50–£150 — but the labour is what drives the cost. On most cars, the top half of the engine has to be partially dismantled to reach the gasket, which typically takes 6–12 hours and means the car is off the road for at least 2–3 days. If the cylinder head has warped from overheating, it will need machining or replacing, which adds significantly to both the cost and the time.
 

Is It Worth Repairing?

This comes down to comparing the repair quote to what the car is actually worth, not just the size of the bill on its own.

• If you've caught it early - white smoke or mild mayonnaise residue, but no significant overheating yet - and the car is otherwise in good condition and worth meaningfully more than the repair cost, fixing it is usually the sensible option.
• If the car has already overheated badly, or the garage is quoting for a warped head or potential engine damage, the repair cost can easily approach or exceed the value of an older or higher-mileage car. At that point, repair becomes a loss-making decision.
• Temporary fixes - sealant additives poured into the radiator - exist and are inexpensive, but they're a short-term measure at best, often lasting only a few weeks to a few months, and aren't a substitute for proper repair if you intend to keep driving the car normally.

Can I Sell a Car With a Blown Head Gasket?

Yes. You don't need to repair the engine, pass an MOT, or even get the car running again before selling it. The only document required is the car's V5C registration certificate - not a service history, not a current MOT, and not proof of any repair work.

You're not obligated to fix the fault before selling; you simply need to be upfront about the car's condition. This is usually where private sales and trade-ins fall down - most private buyers and dealers won't take on a car with a known head gasket issue - but specialist buyers exist specifically for cars in this condition.
 

Why Sell to Sell The Car Instead of Repairing or Scrapping

If the repair bill doesn't make financial sense against the car's value, selling as-is avoids the cost and risk of continuing to drive a car that could overheat and fail completely at any time.

• Free collection, anywhere in the UK — including cars that have already overheated and won't run, so there's no need to risk driving it to a garage or buyer.
• No need to fix anything first — sell the car exactly as it is, smoke, mayonnaise, and all.
• Just your V5C — no MOT, no service history, no chasing paperwork.
• Payment before collection, no haggling — the price you're offered is the price you're paid.
• We've been buying damaged and non-running cars since 2009, so a blown head gasket is a routine purchase for us, not a problem you need to talk us into.

Enter your registration number for a free, no-obligation valuation, and we'll take it from there.
 

FAQs

Can I keep driving a car with a blown head gasket?
It's strongly discouraged. Even short journeys can cause the engine to overheat further, warp the cylinder head, or lead to complete engine failure. If you're seeing clear symptoms, it's safer to stop driving and arrange recovery rather than risk turning a repairable fault into a written-off engine.
 

Is a blown head gasket covered by insurance?
No. It's a mechanical wear-and-failure issue rather than an insured event like an accident, so standard car insurance won't cover the repair. Some extended warranties may include cover, depending on the policy terms.
 

Do I need an MOT to sell a car with a blown head gasket?
No. A car can be sold with no valid MOT and in any mechanical condition. An MOT is only required to drive on public roads, not to transfer ownership.
 

Is white exhaust smoke always a sign of a blown head gasket?
Not always. A small puff of white smoke on a cold start that clears within a minute or so is usually just condensation and is normal. Thick white smoke that persists once the engine is warm, especially alongside coolant loss or oil contamination, is the combination that points to a genuine head gasket problem.