Blown Head Gasket: Symptoms, Repair Cost and When to Sell

White smoke from the exhaust, a temperature gauge that keeps creeping up, and a coolant reservoir that empties itself with no puddle under the car. If that sounds familiar, there’s a good chance you’re dealing with a blown head gasket.

It is one of the repairs owners dread most, and for good reason. The part itself is cheap. Getting to it is not. Here’s how to spot the symptoms, what usually causes the failure, what the repair tends to cost in Australia, and how to decide whether the car is worth fixing.

What does a head gasket do?

The head gasket sits between the engine block and the cylinder head. It seals the combustion chambers so the engine keeps its compression, and it keeps coolant and oil in their own passages so they never mix.

When it “blows”, that seal fails. Depending on where it fails, you can lose compression, push combustion gas into the cooling system, burn coolant in the cylinders, or let coolant and oil mix. Each one shows up as a different symptom, which is why a blown head gasket can look like several problems at once.

Blown head gasket symptoms

These are the signs mechanics look for first. One on its own can have other causes. Two or three together is a strong hint.

White smoke from the exhaust

Thick white smoke that smells sweet, and keeps coming after the engine is warm, often means coolant is getting into the cylinders and being burnt. A little vapour on a cold morning is normal. Clouds after a 20 minute drive are not.

Losing coolant with no visible leak

If you keep topping up the coolant and there’s no drip on the driveway, it has to be going somewhere. Inside the engine is the usual answer.

Overheating

Combustion gas forced into the cooling system creates air pockets and pressure, so the engine runs hot even when the radiator and fan are fine.

Bubbles in the radiator or overflow tank

With the engine running (and only when it is safe to look, never by opening a hot radiator cap), steady bubbling in the coolant points to exhaust gas leaking into the cooling system.

Milky oil

Pull the dipstick or look under the oil filler cap. A creamy, milky sludge that looks a bit like caramel thickshake means coolant is mixing with the oil. That is bad news for the bearings and needs attention quickly.

Rough running and loss of power

A gasket that fails between two cylinders lets them leak into each other, which can cause misfires, a rough idle and a car that feels flat when you accelerate.

Mechanics confirm the diagnosis with a cooling system pressure test, a compression or leak-down test, or a chemical test that detects exhaust gas in the coolant. It is worth paying for one of these before agreeing to a big repair.

What causes a blown head gasket?

Overheating is the big one. When an engine gets too hot, the metal expands, and an aluminium cylinder head can warp enough to break the seal. That overheating usually starts somewhere else: a slow coolant leak nobody noticed, a failed water pump, a stuck thermostat, a cracked radiator or a cooling fan that stopped working.

Age and kilometres play a part too. Gaskets can simply wear out on high-kilometre engines, and engines that have overheated once are more likely to fail again if the root cause was never fixed.

Can you drive with a blown head gasket?

You can sometimes limp a car a short distance, but it’s a gamble. Every kilometre with coolant in the oil or an engine running hot raises the chance of a warped head, damaged bearings or a seized engine. At that point a gasket job becomes an engine replacement.

If you are seeing the symptoms above, park it and get it checked. If the car needs to be moved, a tow is cheaper than a new engine.

What about head gasket sealer?

Sealer products poured into the cooling system can sometimes slow a small leak. Most mechanics treat them as a short-term patch at best, not a repair, and they won’t fix a warped head or a bad leak between cylinders.

How much does it cost to fix a blown head gasket?

Head gasket replacement is labour heavy. The cylinder head has to come off, which on many engines means removing the intake, exhaust, timing components and more. mycar, a national car service chain, says the job typically costs upwards of $1,200.

That is the starting point, not the ceiling. The bill climbs when:

• The cylinder head is warped and has to be machined flat, or replaced
• The engine is a V6 or V8 with two heads, or is tightly packaged in the engine bay
• The timing belt or chain, water pump or thermostat should be replaced while everything is apart
• Coolant in the oil has already damaged bearings or other internal parts

Ask for a written quote that lists the labour hours, the parts, and what happens if the head needs machining once it is off.

Is it worth fixing a blown head gasket?

It comes down to two numbers: what the repair will cost, and what the car will be worth once it’s fixed.

Fixing usually makes sense when the car is fairly young, otherwise in good condition, and the quote is a small share of its value. It makes less sense when the car is older or high kilometre, already needs tyres, brakes or other work, or when the quote is close to (or above) what the car would sell for in good running order.

Not sure what your car is worth right now? Our guide on how much your car is worth walks through free ways to get a realistic figure.

Selling a car with a blown head gasket

Private buyers rarely want a car that doesn’t run properly, and dealers will price the repair, plus a margin, off any trade-in offer. That leaves a lot of owners stuck with a car in the driveway.

Cash For Autos buys cars with mechanical problems across Melbourne, running or not, registered or unregistered. You don’t need a roadworthy. We give you a quote based on the make, model, age and condition, pick the car up for free, and pay you when we collect it.

See cash for cars or unwanted car removal, or call 0424 633 535. Before pickup, check our list of documents you need to sell your car.

Frequently asked questions

What are the first signs of a blown head gasket?

Usually coolant that keeps disappearing without a leak, white exhaust smoke once the engine is warm, and the engine running hotter than normal. Milky oil and bubbles in the coolant are stronger signs.

How much does it cost to fix a blown head gasket?

mycar says head gasket replacement typically costs upwards of $1,200. Warped heads, bigger engines and extra parts replaced at the same time can push it well past that.

What causes a blown head gasket?

Most failures follow overheating, often from a coolant leak, failed water pump, stuck thermostat or faulty fan. Age and high kilometres also play a part.

Can a blown head gasket damage the engine?

Yes. Driving with coolant in the oil or an engine that keeps overheating can damage bearings, warp the head and, in the worst cases, ruin the engine.

Can I sell a car with a blown head gasket?

Yes. It will be worth less than the same car running well, but car buyers like Cash For Autos buy cars with engine problems as they are and tow them away for free.

This guide is general information, not a diagnosis. Have a qualified mechanic inspect your car before you decide on repairs.

Featured image: Image by jcomp on Freepik