What is a compression testing? How does a compression test work? What is the purpose of a compression test? What is a “wet compression test”?
Even though today’s internal combustion engines have powerful designs, eventually they will fail. Most car owners are aware that an internal combustion engine produces power by compressing the vaporized fuel within its combustion chamber. Over time, vital parts like piston rings or cylinder heads components wear out, reducing the amount of compression needed to burn fuel and oxygen effectively. It is crucial to understand how compression testing works in order to diagnose and repair engine problems.
We’ll explain in this article what a compression testing is, when it should occur, and how it’s performed by a professional mechanic.
What is a Compression Test?
The word compression is defined as pressure or compression pressure in the dictionary. To determine the condition of an engine’s internal parts, compression testing is performed. The components of your vehicle may not be working properly.
Over time, parts like intake and exhaust valves as well as valve seats and cylinder seals wear out. Wear can cause pressure to decrease and escape. This results in a higher engine power consumption. Engine power is reduced by using less fuel mixture and air under pressure.
The compression is measured in PSI or bar. Manufacturers generally consider a compression loss of 10% to be normal, even though each engine has a different compression level.
When is a compression test necessary?
If your vehicle displays the following symptoms, a compression test may be required.
- – If smoke is coming from the exhaust system,
- – If you feel your vehicle lacks power or acceleration
- – If the engine vibrates while you drive,
- – If your vehicle is starting to burn faster than normal
- – If the oil is being lost more often than normal
- – If your vehicle’s engine heats too much.
What is the Compression Testing?
1. Turn the engine on to normal operating temperature
Piston rings and valve seats are designed to expand with heat to produce the required compression ratio within the engine.
Run your engine for 5-10 minutes if it is cold before you start the test. After 10 minutes, turn off the engine and wait. After the vehicle is removed from the road, allow it to cool for at least 30 min. It should be warm, not too hot.
Also, you can do a compression test with a cold engine. It is better to test the engine while it is warm. You can then identify any problems and repair them.
2. For protection, wear safety glasses and gloves with insulation
Avoid burns by wearing heat-resistant gloves when you are handling hot parts. Safety glasses are great for protecting against fuel and oil leaks while removing engine components.
– There are rarely any fuel or oil drops on you while testing. But, this precaution shouldn’t be overlooked.
You do not need gloves to test on cold engines.
3. Close the Hood and Stop Engine
To complete the compression test, the engine must be turned off. To safely remove engine components, take out the key from the ignition. You must disconnect the fuel pump relay cable, ignition coils or pen coil cable, if applicable. During the test, the ignition system as well as the fuel system must be disengaged.
You can also unplug the fuel pump cable instead of unplugging it. The fuel pump fuse is typically blue but may vary depending on the vehicle.
4. Disconnect Spark Plugs
Remove all spark plugs from the socket and unplug them. Label the cables. You can’t be confused about which wire goes to which spark plug. Some vehicles use an ignition coil rather than a spark plug. The ignition coils must also be taken apart.
It is also important to identify which spark plug should be removed from which engine cylinder. Label the spark plugs as well as the cylinders.
You should inspect the condition of the taken spark plugs. Replace them if they are worn. Engine problems can be identified by burnt oil and other symptoms.
5. Insert the Compression Tester connector into the Spark Plug Slot of Cylinder 1,
Each cylinder is tested for compression. It is best to begin with the first cylinder and work your back.
Most engines have cylinder 1 located to the right. It is located at the crank pulley’s side. Place the tester tip here, and rotate it clockwise until it clicks in place.
Many compression testers come with multiple adapters. Choose the one that fits your vehicle best.
You should use a measurement device that has a higher compression tolerance if you are testing a diesel-powered engine.
Some testers plug directly in to the engine. These testers do not require an intermediate hose connection to the indicator. This tester does not use the intermediate hose connection. Test results will be affected if the hose is not properly connected.
6. 4. Briefly crank the engine four times
For 3-5 seconds, start the engine. You should crank the engine for at least 4 revolutions. Each piston will have its own pressure reading.
Take a look at the table you see after you have completed all the reels. You should consider the difference between each of the cylinders. You may have a compression leak if the cylinders differ by more than 10 percent.
Wet compression test
Pour some engine oil into any cylinder that is lower than the minimum value, or has a greater difference than the maximum. Measure again. 1 teaspoon of 4.9 ml oil. Then, attach the pressure gauge again and the hose adapter. Then turn the ignition several more times to repeat the test. Check the results again after you are done.
How to interpret the results of a compression test?
Tests done wet will often show a higher pressure reading. This will allow you to identify the problem with your cylinder. The piston rings may be worn if the values are higher. The cylinder is filled with oil that is one to two times the engine oil number. This oil is then measured again. The rings will be responsible for any increase in the values. If the values do not recover, the valves will be deemed defective.
If compression in adjacent cylinders is still low, the cylinder gasket or cylinder head could be damaged. The engine might need to be rebuilt in this instance.
We can see that the combustion chamber will bind soot if the pressure is higher than normal. This can also happen if you use too much thick oil.
If all cylinders have low pressure, it may be necessary to replace the timing belt.
The engine compression level is normal if you have the appropriate data for your vehicle’s engine.
