What are the first signs of a blown head gasket?

A blown head gasket is a serious issue that can lead to extensive engine damage if not addressed quickly. Some of the first signs that your head gasket may be failing include:

Engine Overheating

One of the most common signs of a blown head gasket is engine overheating. The head gasket seals the cylinders and allows coolant to flow through the engine block and radiator. If the seal fails, coolant can leak out leading to overheating. You may notice the temperature gauge reading higher than normal or your “Check Engine” light coming on due to overheating.

White Exhaust Smoke

When a head gasket fails, it allows coolant to mix with the air and fuel in the combustion chambers. This will cause white smoke to come out of the exhaust as the coolant burns off. The smoke may have a sweet smell to it as well. If you notice white smoke coming from your exhaust, especially when the engine is warming up, it could signify a blown head gasket.

Coolant Leaks

With a damaged head gasket, you may notice leaks of coolant from the engine. Check around the cylinder head, intake manifold, radiator and hoses for signs of leaking coolant. Coolant leaks can quickly lead to overheating so keep an eye out for any drips or puddles under your car. The coolant itself may also appear foamy or contaminated.

Misfire or Rough Idling

If combustion gases are leaking through a blown gasket, it can cause engine misfires. This leads to rough idle, loss of power, and poor engine performance. The engine may shake or vibrate more than usual when idling. You may also notice abnormal engine noises or detonation/knocking coming from the cylinders.

Loss of Coolant and Overheating

As mentioned earlier, one of the common signs of a blown head gasket is overheating due to coolant loss. If you have to keep refilling your coolant frequently, and your engine keeps overheating, it likely means there is a leak somewhere in the cooling system. Inspect the head gasket as well as hoses, the radiator cap, water pump, and thermostat housing to check for any external leaks.

Loss of Engine Power

The compression within the cylinders allows your engine to produce power. If combustion gases are escaping through a blown gasket, it reduces compression and engine power. You may notice a lack of acceleration and the engine struggling under loads. Power loss is most noticeable when trying to accelerate and climb hills.

Bubbles in Coolant Tank

If you take a peek into the coolant reservoir tank, bubbles can indicate combustion gases leaking through into the cooling system. The head gasket seals the cylinders and prevents gases from mixing in. So bubbles in the overflow tank likely mean the seal has been compromised and your head gasket is blown.

Milky Oil

When coolant mixes with engine oil it can create a milkshake-like consistency. If your oil looks milky or foamy, it’s a telltale sign the head gasket is blown and allowing coolant to contaminate the oil. This can be caused by cracks in the cylinder head or head gasket itself. The issue needs to be fixed right away to prevent extensive engine damage.

Checking for a Blown Head Gasket

If you suspect your head gasket is blown based on the above symptoms, here are some tips to help confirm:

  • Perform a compression test – Use a gauge to measure the compression in each cylinder. Low or uneven compression indicates a bad head gasket.
  • Conduct a leak down test – This can identify exactly where compression is leaking whether it’s a gasket, piston ring, or valve issue.
  • Check for exhaust gases in the cooling system – Use a leak detector fluid or chemical test to look for combustion gases.
  • Perform a cylinder block test – A chemical test can check for exhaust gas leaking into the coolant.
  • Check for external leaks – Look for any coolant, oil or fuel leaks from the cylinder head gasket surface or engine block.

If your diagnostic tests positively confirm the blown head gasket, the cylinder head and gasket will need to be removed and replaced. This typically requires 6-12 hours of labor for most vehicles. The repairs can be expensive especially on newer cars so get a quote from a mechanic before proceeding with the fix. Driving any further with a blown gasket can risk seriously damaging your engine.

What causes a head gasket to blow?

There are a few common reasons that can lead to a blown or failed head gasket:

  • Overheating – Consistent overheating weakens the head gasket material over time leading to failure. This allows coolant and oil to mix together.
  • High mileage – The cumulative strain on the head gasket after high miles can cause the seal to wear out. Most last 60,000 – 100,000 miles.
  • Improper torque – If the head bolts are not torqued to the proper specifications, it can result in leaks between the cylinder and gasket.
  • Warped or cracked heads – Physical damage to the cylinder head or engine block surfaces prevents the gasket from sealing properly.
  • Modifications – Aftermarket upgrades like turbochargers, superchargers, or performance chips increase cylinder pressures. This places additional stress on the head gasket over time.

Preventative maintenance is key to avoid blowing a head gasket. Be diligent about engine overheating, change fluids regularly, use the correct torque specifications, and inspect for any leaks or damage early on. This can add years of life to your head gasket.

How much does it cost to replace a head gasket?

On average, the cost to replace a head gasket (not including repairs to damaged components) is typically between $1000-$2000. Here are some estimates for head gasket replacement from different manufacturers:

Vehicle Make Average Cost
Ford – $800-$1600
Chevy – $900-$1800
Toyota – $1100-$2000
Honda – $900-$1700
Nissan – $1000-$1800
VW/Audi – $1500-$2500
BMW – $1800-$2800

Labor will account for a large portion of the overall expense. The repair requires 6-12 hours in most cases for disassembly, replacing the gasket, and reassembly. The cylinder head itself may also need to be resurfaced or checked for damage adding to the costs.

While the bill can be steep, delaying the repairs will only increase the extent of the damage. Addressing a blown head gasket quickly is crucial to avoid fully destroying the cylinder head or engine block.

Can you drive with a blown head gasket?

It’s never recommended to continue driving once you’ve diagnosed a blown head gasket. While you may be able to limp the vehicle home, extended driving can lead to catastrophic engine failure.

When combustion gases leak through the compromised gasket seal into the coolant passages, it can cause the engine to overheat rapidly. Driving in an overheated state for even short periods risks severe damage like cylinder head warpage, piston seizure, or rod bearing failure.

The contaminated exhaust can also foul out the catalytic converter and oxygen sensors. Oil that is mixed with antifreeze can damage bearings and other friction surfaces. Any of these issues adds to the overall cost of repair down the line.

In some minor cases, very short drives may be possible if it’s an emergency. But the vehicle should be towed to a shop for diagnosis and repair as soon as possible. Continuing to run errands or commute to work with a blown head gasket is asking for complete engine failure.

Can you fix a blown head gasket with sealant?

Head gasket sealants or “block seal” products claim to stop leaks from a blown head gasket. However, these should be considered temporary emergency fixes at best in most situations.

The sealants can potentially clog small leaks between the engine block and gasket. But they don’t actually repair the underlying issue or restore proper sealing. Driving for long periods with sealant rather than replacing the gasket can lead to overheating episodes or further degradation.

For minor external coolant leaks, sealants may plug the leak for short-term drivability. But internal leaks between cylinders will require a proper gasket replacement to prevent further damage. Only attempt small external leaks if you’re in an emergency spot and can have the gasket replaced immediately after.

How to prevent blowing a head gasket

You can help avoid blowing a head gasket in the first place by:

  • Maintaining proper coolant levels – Prevent overheating and change coolant at recommended intervals.
  • Tuning up the cooling system – Service water pump, thermostat, hoses, radiator cap when needed.
  • Fixing external leaks early – Address any drips, seeps, or external leaks as soon as possible.
  • Checking torque specs – Ensure head bolts are always torqued to factory specifications.
  • Using quality gaskets – Buy gaskets from reputable brands and check for latest revisions.
  • Upgrading head studs – Aftermarket head stud kits help maintain torque consistency.
  • Avoiding overheating – Don’t push the engine when hot or rev excessively.
  • Tuning conservatively – Limit aggressive tuning and high boost with forced induction.

Being diligent about engine maintenance and avoiding overheating is the best way to maximize head gasket life. While they will eventually need replacement, you can get over 100,000 miles by servicing your cooling system and addressing any minor external leaks early.


Catching the early signs like overheating, white smoke, or coolant leaks can help prevent the need for extensive repairs from a blown head gasket. While you may be able to limp a vehicle home, extended driving should be avoided once you’ve diagnosed the issue. To prevent problems, maintain proper operation of your cooling system, keep up with tune-ups, and don’t skimp on gasket quality during engine rebuilds. Address any minor oil or coolant leaks promptly as well. While head gaskets typically last at least 60,000 miles, being diligent with maintenance and tuning conservatively can extend their lifespan further.

Leave a Comment