A Bad Head Gasket
Cars,  Auto Engines

How to Test for a Bad Head Gasket: Signs To Watch Out For

Your car’s engine is composed of different parts, each with a crucial role to play in its overall performance. Among others, one of the most important is the head gasket. It has the primary function of sealing in the combustion process while also minimizing the likelihood that the engine oil and coolant will get mixed in the combustion chamber.

To test for a bad head gasket, you can perform several tests, including testing for hydrocarbons ( unburnt gases from combustion), testing for cylinder pressure, checking the oil for coolant or contaminants, checking the coolant for oil or bubbles, checking the spark plugs for discoloration, and noticing when the engine is overheating or not working properly. 

Looking out for warning signs that show the head gasket is not functioning correctly. If it is already blown, a replacement or repair is necessary as soon as possible.

Over time, the head gasket is subject to wear and tear, which can lead to head gasket problems. A blown head gasket means that the gasket has a break in it, even if it is very small, and oil, coolant, and gases can mix or leak out. As a result, the engine can malfunction, and its power can be reduced. To prevent this from happening, you need to know how to test for a bad head gasket.

What You Will Need to Follow this Tutorial?

In most of the steps that will be mentioned below, you will not need tools as most of the signs are visual. Nonetheless, if there are materials that may be needed, here are what you should prepare:

  • Gas analyzer
  • Probe
  • Compression tester

Step-by-Step Guide on How to Test for a Bad Head Gasket

When testing if the gasket is blown, it is important to determine if it is really the head gasket or something else. If so, a replacement gasket is necessary. If the tests reveal that the head gasket is not bad, you need to proceed with the diagnosis of the other parts until you are able to determine the source of the issue.

Before proceeding, watch this short video below for a primer on the next steps outlined in the article.

1. Check for the Possible Contamination of Oil

The engine oil is one of the most obvious indicators of a potential problem in the head gasket. Before you proceed, make sure to turn off your car and allow the engine to cool down. The least that you would want is to burn yourself while working. Open the engine oil cap or look at the dipstick to see if the oil is discolored or contaminated. If there is a problem, there should be a milk-like ring.

Checking engine oil dipstick in the car

However, take note that this is only a preliminary procedure. Even if the engine oil seems fine, the head gasket could still have a hole in it. To be sure if there is a problem with a bad gasket, continue with the other tests that will be briefly tackled below.

2. Inspect the Coolant

coolant system

The next thing that you have to check is the coolant. You may see oil in the coolant, and it can sometimes be a bad head gasket or a couple of other issues. 

Specifically, you have to look for the presence of hydrocarbons, which means that there are unburned fuel gases in the coolant. If you have these gases in any cooling system, you can detect them with the use of a to find their way there unless there is a broken head gasket.


The best way to check for the presence of hydrocarbons and unburned fuel is through the use of a gas analyzer, which has been shown in the video posted above.

An external leak from the coolant is also indicative of the problem. Watch out for signs of leaks along the surface of the head gasket.

3. Look for Bubbles

car automobile coolant lid antifreeze water plug radiator concep

When testing for a bad gasket, you also have to look at the radiator and check if there are bubbles. To confirm if there are air bubbles, remove the cap that covers the radiator after the engine has cooled for at least 30 minutes.

Start the engine and rev it a few times. If bubbles are forming, this may indicate that your head gasket is leaking gases and is broken somewhere.

4. Check the Spark Plugs

car spark plugs

Another sign that you have a bad head gasket is when you have colored tinted spark plugs. Usually, you will notice that there are white deposits surrounding the spark plugs. This is a result of the burning of the coolant in the combustion chamber. 

If you use a green coolant and if you see greenish particles in the head gasket, take this as another indication of a head gasket problem.

5. Look for Problems in the Engine

Problems in the Engine

The engine will not function properly if the head gasket is blown. One of the problems that will likely occur is an overheating engine. This is because the engine is not able to receive the right amount of coolant. A bad head gasket can also cause overheating during the combustion process.

6. Perform a Cylinder Compression Test

measures the compression in the cylinder of a ca

This is one of the tests that you can perform to determine if there is a problem with the head gasket. The failure of the head gasket can cause low compression and misfire in the cylinders.

To perform a compression test, remove the spark plug(s) and use a compression tester (Video). If it shows low pressure in the cylinders, you may have a problem with the head gasket.

Pro Tips

Below are some tips to keep in mind when dealing with head gaskets, not just when testing if it is bad but also when it comes to care and maintenance:

  • Using the right coolant is one of the easiest ways to prevent the head gasket from being blown. Mixing coolant or using one that is not suitable for your engine can speed up the wear of your head gasket.
  • See to it that the cooling system is in good condition. From the coolant to the water pump, make sure that they are all in good shape. Otherwise, they can cause the engine to overheat and, in turn, will negatively impact the head gasket.
  • When installing a new gasket as a replacement for the one that has been blown, one of the most important is proper sealing. This will prevent the entry of foreign materials and contaminants that can cause wear and tear.
  • Replacing a broken head gasket can be expensive. Good thing there are products that can effectively provide a temporary remedy to the problem. There are products that can seal cracks and gaps in a head gasket, but most people don’t recommend them as a proper or permanent fix. 

The video below shows one last alternative to check for a blown head gasket.


I hope that you can find any problems with your engine as you check for a bad head gasket. As discussed above, it will require a quick visual inspection of oil, spark plugs, radiator, coolant, and possibly other parts of the engine. Testing for compression and hydrocarbons can also help you know if the head gasket is blown.

As you follow the steps above, your understanding of the problem should be clearer, and that will give you options for your next steps.

Revised 2/20