How to Perform a Compression Test on the Engine in a Dodge Caravanby Contributor
The Dodge Caravan, renamed the Grand Caravan for the 2008 model year, came with either a four-cylinder or a V6 engine under the hood in prior model years. When the minivan 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.
Turn on the engine in the Dodge Caravan and allow the minivan to warm up. If you perform the compression test on a cold engine, the results will not be accurate. Turn off the engine once it is warm and disable the ignition system to avoid electrical shock during the compression test.
Remove all of the spark plugs. If the Dodge Caravan contains a four-cylinder engine, there will be only four spark plugs. If it has a V6 engine, there will be six spark plugs to remove. Check the spark plugs for damage and oil since those are indications of damage within the cylinder.
Place the compression tester into one of the spark plug holes and crank the starter. This will rotate the engine and build compression in that cylinder. Write down the compression number. Do the same for each of the spark plug holes so that there is a compression number for each of the cylinders.
Compare the compression numbers to see if they fall within 10 PSI of each other. Compare each number to the recommended compression ratio as well. For a Dodge Caravan with a 3.3L V6 engine, the compression number should fall within 15 PSI of 9.3:1. If the minivan has a 3.8L V6 engine, the compression ratio is 9.6:1. For a 2.4L four-cylinder engine, the ratio is 9.4:1, and a 2.5L four-cylinder engine has a ratio of 9.5:1.
Add a small amount of motor oil to any cylinders that have a low reading and perform the compression test again. If the compression number increases, you will need to repair the cylinder walls or piston rings. If the number stays the same, the valves or valve seats are the problem.
- The compression ratios for all other size engines and models prior to 2001 vary so check the owner's manual for the correct ratio.
Items you will need
- Compression tester
- Motor oil