How to Perform a Compression Test on the Engine in Cars

by Contributing Writer; Updated June 12, 2017

A compression test is a helpful tool used to diagnose engine trouble in a Volkswagen car. It is easy to perform and doesn't require tearing apart the engine to see what isn't working properly inside of it. Some common problems revealed by this simple test include worn valves, piston rings and cylinder walls.

Under The Hood:

 How to Perform a Compression Test on the Engine in a Dodge Caravan

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.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a Chevy Silverado

Turn on the engine in the Chevy Silverado to warm it up, since a compression test performed on a cold engine will be inaccurate. The battery should be in good condition so you can spin the engine several times.

Remove all eight spark plugs from the V8 engine after it is warm and turned off. Models containing a V6 engine have only six spark plugs. Disable the ignition system to eliminate the possibility of electrical shock while performing the compression test.

Insert the compression tester into one of the spark plug holes and crank the starter so that compression builds in that cylinder. Write down the compression number for comparison later and continue to the next spark plug hole. Repeat the procedure for each of the six or eight cylinders, recording each number.

Compare the compression numbers to manufacturer specifications. If the Chevy Silverado contains a 4.3 L V6 engine, the ideal compression ratio is 9.2:1. If it contains a V8 engine, the ratio varies by engine size. A 4.8 L engine is 9.5:1, a 5.3 L engine is 9.5:1 and a 6.0 L engine is 9.4:1.

Evaluate the difference between the recommended compression ratio and the test results. An ideal reading falls within 15 psi. Compare the numbers with each other as well. They should be within 10 psi of each other.

Retest any cylinders that show a low reading by adding a tiny amount of motor oil to the cylinder, then running the compression test again. If the resulting number is higher than the first, then the engine has worn cylinder walls or piston rings in that cylinder. If the number remains the same, then the engine has worn valves or valve seats.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a Chevy Cobalt

Turn on the engine in the Chevy Cobalt and let it warm up since performing a compression test on a cold engine will provide inaccurate results. The battery must be in good condition for the test. Once the engine is warm, turn it off before proceeding with the test.

Remove the spark plugs and disable the ignition system by pulling the coil wire or disabling the ignition coil. Be sure to do this before testing to avoid electrical shock.

Insert the compression tester into one of the four spark plug holes and crank the starter to rotate the engine. After building compression in the cylinder, write down the compression number. Do the same for the other three cylinders in the Chevy Cobalt.

Compare the four compression numbers to manufacturer specifications as well as each other. The compression ratio for the engine of a Chevy Cobalt depends on the engine size. It is 9.5:1 for a 2.0 L engine, 10:01 for a 2.2 L engine and 10.4:1 for a 2.4 L engine. Ideal readings fall within 15 psi of the recommended number and within 10 psi of each other.

Repeat the compression test on any of the cylinders showing a low reading. However, add a capful of motor oil to the cylinder before doing so. If this procedure results in a higher test number, then you have worn cylinder walls or piston rings. If the number doesn't change, then you have worn valves or valve seats.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a Nissan Altima

Warm up the engine in the Nissan Altima prior to testing, since running a compression test on a cold engine will produce inaccurate results. The battery should be in good shape since it will need to spin the engine several times during the test.

Disable the ignition system to avoid electrical shock during the test and remove the spark plugs from the engine. If the car contains a V6 engine, there will be six spark plugs, but if it has a 4-cylinder engine, there will be only four spark plugs. Examine the spark plugs for oil or damage, since these are signs of problems within that cylinder.

Place the compression tester in one of the spark plug holes and crank the starter. This rotates the engine and builds compression in that cylinder. Write down the resulting number. Continue testing each of the remaining cylinders in the same fashion, recording the compression numbers. When you finish, there will be either four or six compression numbers, one for each cylinder.

Compare the compression numbers to manufacturer specifications. A Nissan Altima with a V6 engine has a compression ratio of 10.3:1, but for one with a 4-cylinder engine, the ratio varies by model year. If the model year is 1993 through 1999, the ratio is 9.4:1. For 2000 and 2001, the ratio changes to 9.2:1, and the ratio for 2002 through 2007 is 9.5:1.

Evaluate the test results. Compression numbers should fall within 15 PSI of the recommended compression ratio. Numbers should also fall within 10 PSI of each other. Retest any cylinders with low compression numbers.

Add a small amount of motor oil to the cylinder before performing the compression test again. If the number increases, the cylinder contains worn piston rings or cylinder walls. If the number is unchanged, it has worn valves or valve seats.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a Honda CR-V

Prepare for the compression test by warming up the engine in the Honda CR-V. Performing a compression test on a cold engine will produce inaccurate results. Make sure the battery is in good shape since it will need to spin the engine many times during the test.

Begin by removing all four spark plugs from the engine and disabling the ignition system. This will prevent electrical shock while performing the test. The engine can now spin freely.

Place the compression tester in one of the spark plug holes and crank the starter. This rotates the engine and builds compression in the cylinder. Record the compression number and continue to the next spark plug hole. Repeat the process until you test all four cylinders and record the compression numbers.

Evaluate the test results by comparing these four numbers to recommended manufacturer specifications. If the Honda CR-V is a 2007 or a 2008 model, the compression ratio is 9.7:1. For model years between 1999 and 2006, the ratio is 9.6:1. If the SUV is one of the earliest models, 1997 or 1998, the ideal ratio is 9.0:1. Compression numbers should be within 15 PSI of these suggested ratios.

Compare the compression numbers to see if they are within 10 PSI of each other. If any cylinder has a low reading, perform the compression test again after adding a small amount of motor oil to that cylinder. If the compression number increases, worn piston rings or cylinder walls are present. Worn valves or valve seats are the problem if the number does not change.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a Toyota Camry

Warm up the engine in the Toyota Camry before performing the compression test since running one on a cold engine produces inaccurate results. Make sure that the battery is in good condition, since it will need to spin the engine several times.

Disable the ignition system to avoid electrical shock during the test. Remove all of the spark plugs and check each one for damage, since it is a sign of damage within the cylinder. If the Toyota Camry contains a 4-cylinder engine, there will be four spark plugs, but if it has a V6, there will be six.

Insert the compression tester into one of the spark plug holes. Crank the starter to rotate the engine and build compression within the cylinder. Write down the compression number for that cylinder.

Repeat the test on all of the cylinders, keeping a record of the compression numbers. Compare them to each other. They should be similar and fall within 10 PSI of each other.

Compare the compression numbers to the recommended compression ratio. If the Toyota Camry contains a 3.5L or 3.3L V6 engine, the compression ratio is 10.8:1. If it has a 3.0L V6 engine, the ratio is 10.5:1. The compression numbers should fall within 15 PSI of the compression ratio.

Add a small amount of motor oil to any cylinders that have a low compression number and perform the compression test again. If the number increases, the cylinder was worn walls or piston rings, but if it remains the same, there are worn valves or valve seats within the cylinder instead.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a Toyota Corolla

Prepare for the compression test by warming up the engine in the Toyota Corolla. Performing the test on a cold engine produces inaccurate results. The battery must be in good condition, since it will need to spin the engine several times during the test.

Stop the engine and disable the ignition system to avoid electrical shock. Remove each of the four spark plugs, checking them for oil or damage, since these are signs of damage within the cylinder.

Place the compression tester in one of the spark plug holes and crank the starter. Rotating the engine builds compression in the cylinder, causing the needle on the gauge to jump. The last number that it jumps to is the compression number for that cylinder.

Write down the compression number and move on to the next spark plug hole. Repeat the procedure until you test all four cylinders and record the compression numbers. Compare these numbers to see if they fall within 10 PSI of each other.

Compare the compression numbers to the recommended compression ratio to see if they fall within 15 PSI. If the Toyota Corolla contains a 1.8L engine, the compression ratio is 10.0:1. However, if it is a 1.8L engine with 164 or 170 horsepower, the ratio changes to 11.5:1. For engines other than the 1.8L, check the vehicle manual for the appropriate compression ratio.

Perform the compression test again on any cylinders with a low compression number after adding a capful of motor oil to the cylinder. If the compression number increases, the cylinder has worn piston rings or cylinder walls. If the number stays the same, there are worn valves or valve seats instead.

Items you will need

  • Compression tester

  • Motor oil

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

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.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a Ford F-Series

Warm up the engine in the Ford truck completely before performing the compression test. Running the test on a cold engine produces inaccurate results. Be sure that the engine in the truck is in good shape since it will need to spin the engine several times during the test.

Disable the ignition system to avoid the possibility of electrical shock during the compression test and remove all of the spark plugs from the engine. If the truck contains a V6 engine, there will be only six spark plugs, but if it contains a larger V8 or V10 engine, there will be either eight or ten spark plugs. Inspect the spark plugs for damage since this is a sign of problems within that cylinder.

Insert the compression tester into one of the spark plug holes and crank the starter. This rotates the engine and builds compression within the cylinder. Record the compression number and repeat the procedure for each of the remaining cylinders. There will be a record of six, eight or ten numbers when you finish, depending on the engine size.

Compare the compression numbers to the recommended compression ratio for a Ford F-series truck to see if they fall within 15 PSI of that number. For an F-150 with a V6 engine, the compression ratio is 9.2:1, and for one with a 5.4L V8 engine, the ratio is 9.8:1. For both F-250 and F-350 trucks with a 6.0L V8 engine, the ratio is 18.0:1, but if the truck contains a V10 engine, the ratio for 2007 and 2008 models of these trucks is 9.2:1 and 9.0:1 for the 2004 through 2006 models. Compression ratios vary for all other V8 engines in these models by year and liter.

Evaluate the results by comparing the compression numbers to each other as well. They should be similar and fall within 10 PSI of each other. Retest any cylinders with a low reading after adding a small amount of motor oil to the cylinder. If the number increases, the cylinder contains worn walls or piston rings, but if it stays the same, there are worn valves or valve seats instead.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a Subaru Outback

Begin by warming up the engine in the Subaru Outback, since running a compression test on a cold engine produces inaccurate results. Make sure that the battery is in good condition, since it will need to spin the engine several times.

Disable the ignition system to avoid the possibility of electrical shock and remove all of the spark plugs. If the Subaru Outback contains a 6-cylinder engine, there will be six spark plugs. If it has a 4-cylinder engine, there will be only four.

Insert the compression tester into one of the spark plug holes and crank the starter. This rotates the engine and builds compression in the cylinder. Write down the compression number and move on to the next hole. Repeat the compression test on each of the cylinders, keeping track of the results.

Check the compression numbers to see if they fall within 15 PSI of manufacturer specifications. If the Subaru Outback contains a 6-cylinder engine, the compression ratio is 10.7:1. Most models with a 2.5L 4-cylinder engine have a ratio of 10.0:1, but some vary so check the vehicle manual to be sure.

Compare the compression numbers to each other. The numbers should be similar and fall within 10 PSI of each other. If any cylinder has a low reading, add a little motor oil to it and run the compression test again. If the compression number remains the same, the cylinder has worn valves or valve seats. If it increases, the cylinder has worn walls or piston rings instead.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a Kia Spectra

Begin by warming up the engine. Performing the compression test while the engine is cold will produce inaccurate results. The battery must also be in good condition so that it can spin the engine several times during the test.

Turn off the engine before continuing. Disable the ignition system to avoid electrical shock and remove all four spark plugs from the engine. It can now spin freely.

Test the first cylinder by placing the compression tester in the spark plug hole and cranking the starter. This rotates the engine and builds compression in that cylinder. Keep a record of each of the compression numbers for comparison later on.

Repeat this procedure, testing all four cylinders of the Kia Spectra. The resulting compression numbers should be similar, falling within 10 PSI of each other. Any cylinders with a low reading need to be retested, since there are problems in that cylinder.

Compare the test results to manufacturer specifications for the Kia Spectra. If the model year is 2005-2008, the compression ratio is 10.1:1. If it is 2002-2004, the ratio is 9.5:1. For model years 2000 and 2001, the ideal ratio is 10.0:1. Results from the compression test should fall within 15 PSI of these numbers.

Add a little motor oil to any cylinders that have a low compression number and perform the test again. If this causes the number to increase, the cylinder walls or piston rings are in need of repair. If this doesn't affect the number, the valves or valve seats need repair.

Items you will need

  • Compression tester

  • Motor oil

 How to Perform a Compression Test on the Engine in a VW Jetta

Warm up the engine in the VW Jetta since a compression test ran on a cold engine will not be accurate. Be sure that the battery in the car is in good condition since it will need to spin the engine several times.

Turn off the car and remove all of the spark plugs from the engine; the number varies depending upon engine size. Now the starter can spin the engine freely. Disable the ignition system to avoid electrical shock during the compression test.

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 cylinders, keeping a record of all the compression numbers.

Check to see if the compression numbers fall within 15 PSI of manufacturer specifications for the VW Jetta. If the car contains a five-cylinder engine, an ideal reading is 9.5:1. In models with a four-cylinder engine, the recommended compression ratio varies by engine. If the car contains a 2.0L engine, the ratio is 10.3:1 but if it has a 1.9L engine, the ratio is 18.5:1 instead.

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 number doesn't change, the engine has worn valves or valve seats instead.

Items you will need

  • Compression tester

  • Motor oil