How to tell if your head gasket is blown?

Author: Shanna Bradtke  |  Last update: Tuesday, September 2, 2025

There is an easy way to find out if your engine's head gasket has blown. Simply check under the oil filler cap. If the gasket is not damaged, the inside of the oil cap will be mostly dry. If you discover a milky brownish-yellow substance that is similar to the thickness of a milkshake, you probably have a gasket leak.

What are the first signs of a blown head gasket?

Bad head gasket symptoms
  • White smoke coming from the tailpipe.
  • BUBBLING IN THE RADIATOR AND COOLANT RESERVOIR.
  • unexplained coolant loss with no leaks.
  • Milky white coloration in the oil.
  • Engine overheating.

What can be mistaken for a blown head gasket?

A lot of the problem is due to the similarity between issues with head gaskets and other engine components, such as the following: A chipped or warped cylinder head, which could affect the head gasket, but wouldn't necessarily be the result of a blown head gasket.

How do you test a head gasket?

Bubbles in the coolant is a huge clue. A cooling system pressure test can show if the head gasket failure is leaking into the water jacket. If the spark plug firing end of one plug is bone white, you've likely found the cylinder associated with the head gasket leak.

How does a car act with a blown head gasket?

One of the most common symptoms is an engine that runs poorly. It might have a rough idle, deliver poor acceleration, overheat, or exhibit a combination of all three issues. This happens because the engine makes less power as it loses compression.

HOW TO CHECK FOR A BLOWN HEAD GASKET

How to do a head gasket test at home?

You can remove the spark plugs - if applicable to your model – and look for signs of oil and water. If you notice oil and water on the plugs, this can be an indication of a faulty head gasket. You can purchase a head gasket tester – a block tester – and place it in the water expansion tank with blue dye.

Will a car still run with a blown head gasket?

Technically you can drive with a blown head gasket, but we'd always advise against it.

How do I know if I have a blown head gasket or cracked block?

Conducting a compression test on each cylinder is a valuable diagnostic tool for identifying both a blown head gasket and a cracked block. Significant variation in compression levels between cylinders could indicate a blown head gasket, as the gasket's failure can affect the seal between cylinders.

How much does it cost to fix a head gasket?

On average, you can expect to pay between $1,000 and $3,000 for a head gasket replacement, with the average cost being around $1,500. When choosing a mechanic for a head gasket replacement, it's important to choose a reputable and experienced professional who can provide high-quality work at a fair price.

What does a car sound like with a blown head gasket?

When your head gasket fails, the pressure within the cylinders will not be at the correct level. You may hear a knocking sound emanating from the engine, or the sound of a misfire – depending on how the head gasket blew.

Will a car still crank with a blown head gasket?

Your Car Won't Start.

Is there a warning light for head gaskets?

No. But it would most likely overheat, and that would light up the check engine light. Also; you would see residues on the dipstick (possibly), under the radiator cap (sometimes), and under the oil filler cap (definitely).

How to know if it's a water pump or head gasket?

Loss of coolant

If you notice that the coolant levels within your reservoir or radiator are low, first check for leaks on the outside of the engine, water pump, radiator and other cooling system components. If no leak can be found, it's most likely that your gasket is blown.

Is it worth fixing a blown head gasket?

However, it's not worth repairing if the blown gasket has caused severe damage to the engine block, has high mileage, or other major issues. In these situations, the repair costs may exceed the vehicle's worth and you're better off replacing the vehicle.

Will a blown head gasket throw a code?

The first symptoms of a head gasket that is failing are usually a slow loss of coolant with no visible leaks, engine overheating and/or a Check Engine light with cylinder misfire codes.

Does bubbling coolant always mean blown head gasket?

My car has back-pressure: What should I do? If your vehicle's coolant is bubbling, it is highly likely that your vehicle has a blown head gasket. Take the vehicle to a mechanic for an official diagnosis, and research your repair options. How much does it cost to fix a blown head gasket? >>

What is the cheapest way to fix a blown head gasket?

Follow these guidelines and you'll be back on the road in no time at all:
  1. Remove thermostat and flush the cooling system.
  2. Fill the system with water.
  3. Add BlueDevil Head Gasket Sealer slowly to the radiator as the vehicle idles.
  4. Install the radiator cap and allow the engine to idle for at least 50 minutes.

How long can I drive with a blown head gasket?

When a gasket fails it can do serious damage to your car, so it is important to know the warning signs and what you need to do to get it fixed. Depending on how severe the leak or perforation is, a car usually does not last longer than a month with a blown head gasket.

Will a car run rough with a blown head gasket?

A blown head gasket can lead to a noticeable drop in your engine's performance. You might experience rough idling, misfires, or even a significant loss of power. This happens because the gasket failure causes a loss of compression in one or more cylinders, disrupting the engine's normal operation.

How to tell the difference between a bad head gasket or intake gasket?

Coolant and Oil Mixing: A distinctive sign of head gasket failure is the mixing of coolant and oil, resulting in a milky substance in your oil cap or coolant reservoir. This is rarely associated with intake manifold gasket problems.

How do I know if my cylinder head is bad?

Smoke coming from the exhaust is the clearest indicator that you could have a cracked cylinder head. The crack and damage are most likely to be a lot more severe in this instance.

What are the signs of a head gasket going?

If you are concerned that your head gasket might need to be replaced, look for the following symptoms.
  1. Engine Overheating.
  2. Rough Idle. ...
  3. Visible Tailpipe Smoke. ...
  4. Milky Build-Up Under Oil Cap. There is an easy way to find out if your engine's head gasket has blown. ...

How many hours does it take to replace a head gasket?

DIY head gasket replacement

In most cases, you won't want to replace your head gasket yourself. This fix involves working within the engine in areas that need to stand up to lots of heat and pressure. Even if you're knowledgeable about engines, replacing a head gasket is difficult and will take about five hours.

Does oil in coolant always mean head gasket?

If the oil cooler leaks, the main symptom is oil in the coolant. This can cause many people to think that the head gasket is blown. However, a blown head gasket usually affects the engine's performance. If the oil cooler leaks, the engine will still perform normally.

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