How to Do a Compression Test on a Car Engine

Introduction

A compression test is a diagnostic procedure that measures the pressure in an engine’s cylinders. This information can be used to assess the engine’s condition and identify potential problems. A compression test is relatively easy to perform and can be done with a few basic tools.

What You’ll Need

To perform a compression test, you will need the following:

* A compression tester
* A spark plug wrench
* A screwdriver
* A shop rag

Safety First

Before you begin, it is important to take some safety precautions. Make sure that the engine is cool to the touch. You should also disconnect the negative battery terminal to prevent any electrical shocks.

Step-by-Step Instructions

1. **Locate the Spark Plugs**

Open the hood of your car and locate the spark plugs. They are usually located on the top of the engine, near the center.

2. **Remove the Spark Plugs**

Use the spark plug wrench to remove the spark plugs. Be careful not to drop the spark plugs into the engine.

3. **Insert the Compression Tester**

Screw the compression tester into one of the spark plug holes. Make sure that the tester is seated firmly.

4. **Crank the Engine**

Have an assistant crank the engine over for about 5 seconds. The compression tester will read the pressure in the cylinder.

5. **Record the Reading**

Note the reading on the compression tester. This is the compression pressure for that cylinder.

6. **Repeat Steps 3-5 for the Remaining Cylinders**

Repeat steps 3-5 for the remaining cylinders.

Interpreting the Results

The compression pressure should be within a certain range for your specific engine. You can find the specified range in your vehicle’s repair manual. If the compression pressure is too low, it could indicate a problem with the engine.

Troubleshooting

If the compression pressure is too low, there are a few possible causes:

* **Valves not sealing properly**
* **Piston rings worn or broken**
* **Cylinder head gasket blown**

You can troubleshoot these problems by performing further tests.

Conclusion

A compression test is a valuable diagnostic tool that can help you assess the condition of your car’s engine. This test is relatively easy to perform and can be done with a few basic tools. If you are experiencing any problems with your engine, a compression test can help you identify the cause.