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How to Perform a Compression Test on the Engine in a Hyundai Sonata

by Contributor

The Hyundai Sonata comes with either a 4-cylinder or a V6 engine under the hood. When that engine runs poorly, a simple compression test lets you know what is wrong without tearing apart the engine. Some common problems diagnosed by performing a compression test are worn valves, pistons and rings.

Begin by warming up the engine in the Hyundai Sonata, since performing a compression test on a cold engine produces inaccurate results. Make sure that the battery is in good shape as well, so that it will be able to spin the engine several times.

Turn off the engine and disable the ignition system to avoid electrical shock during the test. Remove all four spark plugs from the engine. If the Hyundai Sonata contains a V6 engine, there will be six spark plugs.

Place the compression tester in one of the spark plug holes and crank the starter. Rotating the engine builds compression in that cylinder. Record the compression number for that cylinder and then do the same for the rest of the cylinders, keeping track of the test results.

Evaluate the compression test results. Numbers should fall within 15 PSI of the recommended manufacturer specifications. For a Hyundai Sonata with a 4-cylinder engine, the ideal compression number is 10.5:1. If it has a V6 engine, the number should be 10.4:1.

Compare the compression numbers to each other. The difference should be no more than 10 PSI. Retest any cylinder that has a low reading by adding a small amount of motor oil to the cylinder and performing the test again. If the number increases, worn cylinder walls or piston rings are present. If the number stays the same, the cylinder has worn valves or valve seats instead.

Tip

  • These compression ratios are for 2006 or newer models of the Hyundai Sonata. For older models, check the vehicle manual for the appropriate compression ratio.

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