How to Perform a Compression Test on the Engine in a VW Beetle
The new VW Beetle contains a five-cylinder engine, although older models had a four-cylinder instead. It is important to keep the engine running properly. Over time, parts inside of the engine wear out causing the car to lose power, burn oil or run poorly. A compression test is an easy way to diagnose common engine trouble.
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Instructions
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Begin by first warming up the engine in the VW Beetle. Performing a compression test on an engine that is cold will produce inaccurate results. Check the battery in the car to be sure that it is in good condition so that it will be able to spin the engine several times.
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2
Disable the ignition system and remove all of the spark plugs. If the car contains five-cylinder engine, there will be five spark plugs, but if it is one of the older models with a four-cylinder engine, there will only be four. The starter can now spin the engine freely.
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Insert the compression tester into one of the spark plug holes and crank the starter. Spinning the engine builds compression in that cylinder, producing a reading on the compression tester. Write down the compression number for that cylinder.
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Repeat this procedure for each of the four or five cylinders, depending on engine size. Compare these test numbers to each other. If they aren't similar and vary by more than 10 PSI, there is a problem. You need to retest any cylinders with a low reading.
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Compare the test results to the recommended manufacturer compression ratio. A VW Beetle with a five-cylinder engine should have a reading of 9.5:1. One with a 2.0L 4-cylinder engine should have a 10.0:1 compression ratio. If the numbers are off by 15 or more PSI, there is a problem.
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Add a capful of motor oil to any cylinders with a low reading before retesting them. If this causes the number to increase, there are worn cylinder walls or piston rings. If the number stays the same, the cylinder has worn valves or valve seats.
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Tips & Warnings
If the VW Beetle has a 1.9L 4-cylinder engine, the compression ratio varies by horsepower. If the engine has 100hp, the ratio is 19.0:1, but if it has 90hp, the ratio changes to 19.5:1. For 1.8L engines, the ratio for 150hp is 9.3:1 and the ratio for 180hp is 9.5:1.
