Ultimate Guide: How to Test Coolant for Exhaust Gases and Ensure Engine Health

It is crucial to regularly test coolant for exhaust gases, ensuring the efficiency of your vehicle’s engine.

The presence of exhaust fumes in your coolant might indicate a variety of engine issues. It could be a leaky head gasket, a fractured engine block, or other sorts of engine damage.

Ignoring these problems can lead to decreased engine performance, costly repairs, and even engine failure.

Fortunately, the coolant test for exhaust gas is a simple, accurate method. You can perform it with a test kit.

In this post, we’ll walk you through the usage of a combustion gas tester. We will also provide you with tips on how to interpret the findings.

What Is Combustion Gas In Coolant Tester?

test coolant for exhaust gases

Combustion gas in the coolant is a major problem that can harm the engine’s efficiency and performance.

It occurs when exhaust gases, such as hydrocarbons and carbon monoxide, enter the cooling system. The gases will be mixed with the coolant.

This phenomenon often appears when there is a burst head gasket or a flawed cylinder head.

They will allow the gases to flow into the coolant pipes. Untreated combustion gas in the coolant can cause various issues. 

Your car may face decreased engine performance, overheating, and probable engine damage.

A simple inspection utilizing a test kit available at most auto parts stores may identify combustion gas in your coolant.

Don’t ignore combustion gases in the coolant. Take steps to protect your engine’s health and avoid expensive costs later.

What Is A Coolant Exhaust Gas Test Kit? 

Anyone who wishes to maintain their vehicle’s engine running smoothly should possess a coolant exhaust gas test kit. It is utilized for identifying the presence of combustion gases in the coolant.

When there is a faulty cylinder head, or a damaged cylinder (s), combustion gases might enter the cooling system.

The color-changing fluid in the test kit will interact with combustion gases, such as carbon monoxide and hydrocarbons.

The chemical reaction will show its presence in the cooling system. By identifying the existence of combustion gases early, you may take measures to prevent future engine damage.

It will save money on repairs later.

A block tester for head gasket is a low-cost, simple instrument. This device may help you save time and money in the long run.

How to Test Coolant for Exhaust Gases: Step-by-Step Guide

coolant test for exhaust gas

By detecting these gases early, you can take action to avoid further damage and costly repairs. This step-by-step guide will show you how to use a block tester for exhaust gases.

Besides, you will also know the testing procedure when there is a blown head gasket with no indicator in the cooling system.

Performing A Compression Test For The Head Gasket

A simple block test can frequently reveal exhaust gases in the engine’s cooling system when there is a burst head gasket.

This type of test for exhaust gas in coolant will be discussed in the following.

On the other hand, a head gasket may blow but display no exhaust gases in the cooling system.

Suppose there is a defective head gasket between two cylinders; the compression from one cylinder will seep into the other.

A compression test can be used to identify it. If the head gasket leaks, white smoke will normally stream out of the exhaust pipe. The overall power will be reduced.

To detect a damaged head gasket in your engine, follow these steps. First, uninstall the spark plugs from the engine.

Then, put a compression gauge into the opening of a spark plug. Now you should start the engine to get the maximum gauge reading. Take notes on the results.

You can repeat this method for the other cylinders. Examine the outcomes of each cylinder.

The head gasket is defective if the reading on two or more contiguous cylinders is much lower than the remainder.

Performing A Block Test 

Follow these steps to perform the block test for head gasket and detect any issues.

Step 1: Take out the pressure cap from the expansion tank or radiator. You need to ensure that the engine coolant level is sufficiently low. It should be around 3′′ below the fill hole.

In case of excessive coolant, remove enough to keep the test fluid from being contaminated. This procedure will stop the coolant from entering the test equipment.

Step 2: Let the engine heat up to the normal operating temperature and idle throughout the test. As this test is in operation, coolant must be flowing.

It will allow the exhaust gases to reach the cooling system. 

Step 3: Before putting the test fluid into your testing equipment, it must be blue liquid. The fluid is past its expiration date if it is yellow or green. You should replace the instrument with blue fluid.

Step 4: Fill a glass tube with test fluid to the mark.

Step 5: Put the test instrument’s cone into the neck of the radiator or expansion tanks. You need to make sure that it is tightly sealed.

Step 6: Place the squeeze bulb on the test device’s top. Then, press it for roughly thirty seconds to draw radiator gases into the test fluid.

Assuming exhaust gases are inside, the fluid in the instrument will “sniff” them as they pass through it.

Once the block tester fluid turns green or yellow, it indicates that exhaust gases are seeping into the coolant system. Now, you need to repair the head gasket.

Step 7: If the fluid stays blue, it means there is no exhaust in coolant tester or cooling system.

Step 8: When a defective head gasket seems possible but the coolant block test kit passes, the head gasket failure might be between the two cylinders.

A car may have a blown head gasket even if no exhaust gases are seeping into the coolant system. A compression test will act as a head gasket damage indicator in this case. Call a professional technician for assistance in determining the cause of the damage.

What Are The Common Causes Of Exhaust Gas In Coolants?

Exhaust gas in the coolant can be a sign of potential engine problems. When it occurs, it is essential to diagnose and address the underlying issue promptly.

It will prevent further damage. Several common causes include overheating, engine cold starts, and time and age.

Overheated Engine

Overheating an engine can allow exhaust gas to get into the coolant system, resulting in a blow-by. High temperatures can cause damage to the cylinder head and head gasket.

It allows combustion chamber gases to leak into the coolant. Overheating is often caused by many issues, including a faulty cooling system, a coolant leak, or a blocked radiator.

Overheating must be addressed immediately to avoid further engine damage and related safety issues.

Radiator cleanings and head gasket replacement or maintenance can assist in avoiding overheating and extending engine life.

Rough Cold Starts

Rough cold starts can cause engine stress, damaging the head gasket. It will lead to the exhaust gas in the coolant.

When the engine is cold, the metal components contract and oil flow is reduced, causing increased friction and wear on engine parts. It can cause the head gasket to fail over time.

Time and Age 

Engine parts can erode over time, resulting in higher blow-by and exhaust gas in the coolant. The bad head gasket might degrade and lose its capacity to seal.

It will allow combustion gases to enter the coolant system.

Aging engine components can also raise the danger of cylinder head or engine block cracks. They can all lead to blow-by.

Regular maintenance with replacing old engine components and changing the coolant can help prevent these problems.

What Are The Costs Of Coolant Combustion Gas Testers And A Blown Head Gasket?

combustion gas in coolant

The cost of a combustion leak detector can vary depending on the brand and model. A basic tester can cost between $20 to $50 on average.

Meanwhile, a more advanced tester with additional features can cost upwards of $100 to $200.

The cost of a blown head gasket issue can also vary depending on the make and model of the vehicle.

The cost can range from $1,000 to $2,000. Some repairs cost as much as $4,000 or more for luxury or high-performance vehicles. This cost includes labor, parts, and machine work.


It is essential to test coolant for exhaust gases to avoid expensive costs later.

Understanding common causes, such as overheating and aging components, can help prevent expensive repairs. Performing a compression or block test can provide further insight into engine health.

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