How to Perform a Compression Test on the Engine in a Dodge Ram
A compression test is a helpful tool used to diagnose engine trouble. It's easy to perform and doesn't require tearing apart the engine to see what isn't working properly inside. Some common problems revealed by performing this simple test on the engine in a Dodge Ram include worn valves, piston rings and cylinder walls.
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Instructions
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Warm up the engine. A compression test ran on a cold engine will be inaccurate. Be sure that the truck's battery is in good condition, since it will need to spin the powerful six- or eight-cylinder engine several times.
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Turn off the engine and remove all of the spark plugs. If the Dodge Ram contains a V6 engine, there will be six, but if it has a V8 engine, there will be eight. Now the starter can spin the engine freely. Disable the ignition system to avoid electrical shock.
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Place the compression tester into one of the spark plug holes and crank the starter to rotate the engine. This builds compression in that cylinder. Record the resulting compression number for comparison later. Repeat this process for each of the six or eight cylinders, keeping a record of all the compression numbers.
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Check to see if these numbers fall within 15 PSI of manufacturer specifications. If the Dodge Ram contains a V6 engine and is a 2005 or newer model, an ideal reading is 9.7:1. If it is an older model, the compression ratio is 9.1:1 instead. If the truck contains a V8 engine, the recommended compression ratio varies by year and engine, so be sure to check the vehicle manual.
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Compare your numbers to each other as well. Each number should fall within 10 PSI of the others. If one cylinder shows a low reading, add a small amount of motor oil to that cylinder and perform the compression test again. If the compression number increases, worn cylinder walls or piston rings are the problem. If the numbers doesn't change, the truck has worn valves or valve seats instead.
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