How to Compression Test an Engine Out of Car

Introduction

A compression test is a diagnostic procedure that measures the pressure inside an engine’s cylinders. This information can be used to identify a variety of engine problems, including:

* Worn or damaged piston rings
* Leaking valves
* Blown head gasket
* Cracked cylinder head or block

A compression test is a relatively simple procedure that can be performed in about an hour. However, it is important to note that a compression test is not a complete diagnosis of an engine’s health. Other tests, such as a leakdown test, may be necessary to pinpoint the exact cause of a problem.

Tools and Materials

You will need the following tools and materials to perform a compression test:

* Compression tester
* Socket wrench
* Spark plug socket
* Rags
* Flashlight

Safety Precautions

* Before performing a compression test, be sure to take the following safety precautions:
* Disconnect the negative battery terminal.
* Allow the engine to cool down completely.
* Wear eye protection.

Procedure

1. Remove the spark plugs.
2. Insert the compression tester into the spark plug hole.
3. Crank the engine over until the compression tester gauge reaches its maximum reading.
4. Record the maximum reading.
5. Repeat steps 2-4 for each cylinder.

Interpreting the Results

The compression test results will vary depending on the engine type and condition. However, as a general rule, the following readings are considered to be acceptable:

* Gasoline engines: 140-180 psi
* Diesel engines: 300-450 psi

If the compression test results are below the acceptable range, it indicates that there may be a problem with the engine. The next step is to perform a leakdown test to pinpoint the exact cause of the problem.

Tips

* If you are having trouble getting a good seal between the compression tester and the spark plug hole, try using a small amount of petroleum jelly on the O-ring.
* If the compression test results are inconsistent, it may indicate a problem with the compression tester. Try using a different compression tester or having the tester calibrated.
* If you are not comfortable performing a compression test yourself, you can have it done by a qualified mechanic.

Conclusion

A compression test is a valuable diagnostic tool that can help you identify a variety of engine problems. By following the steps outlined in this article, you can perform a compression test yourself in about an hour.