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

How to Test for a Bad Head Gasket

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. The latter has the primary function of sealing the combustion process, while also minimizing the likelihood that the engine oil and the coolant will get mixed in the combustion chamber.

Through time, the head gasket can be subjected to wear and tear, which can lead to being blown. As a result, the engine will malfunction and its power will be reduced. To prevent this from happening, you need to know how to test for a bad head gasket. You need to watch out for the warnings that it is already deteriorating. If it is already blown, a replacement or repair is necessary as soon as possible.

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 will 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

Testing if the gasket is blown is important to determine if it is indeed the problem and if a replacement 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 I proceed, watch the short video below for a primer of the discussions in the next section.

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.

However, take note that this is only a preliminary procedure. Even if the engine oil, seems fine, this is in no way conclusive. 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

The next thing that you have to check is the coolant. Specifically, you have to look for the presence of hydrocarbons, which means that there is unburned fuel. If you have an unburned fuel in any cooling system, there is no way that it will be able to find its 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 the leaks along the surface of the head gasket.

3. Look for Bubbles

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, start by removing the cap that covers the radiator. Start the engine and rev it for a few times. If there are bubbles forming, this shows that your head gasket is most probably problematic.

4. Check the Spark Plugs

Another sign that you have a bad head gasket is when you have 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 problem.

5. Look for Problems in the Engine

Problems in the Engine


The engine will also be negatively affected if the head gasket is blown. With this, one of the problems that you will have is an overheating engine. This is because the engine is not able to receive the right amount of coolant. The negative effect of a bad head gasket in the combustion process is another reason for this overheating.

6. Perform a Cylinder Compression Test

This is one of the last tests that you should perform to determine if there is indeed a problem with the head gasket. The failure of the head gasket can cause low compression and misfires in the two cylinders. To perform a compression test, remove the spark plugs and use a compression tester. If it shows low or 0 PSI in two neighboring cylinders, you 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 a 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 be effective in providing a remedy to the problem. There are pop and pour products that can seal cracks and gaps. Chemical repairs are promising, especially if you do it right.


At this point, I hope that you already know how to test a bad head gasket. As it has been discussed above, it will require a quick visual inspection of oil, spark plugs, radiator, and coolant, among other parts of the engine. Testing for compression and hydrocarbons may also be necessary to know if the head gasket is blown.

Have you tried testing for a blown head gasket? Is there anything else that you would like to add? Leave a comment below and let us know.