What Are Diesel Compression Testers Used For?

3 min

Diesel Compression Testers

Cars make traveling more accessible, faster and a bit more reliable than ever before. This human creation has gone through many transformations throughout the years. As car technology evolves, new ways have been engineered to detect car trouble better. Now drivers can find and solve minor car issues with or without a mechanic’s assistance.

Each part of a vehicle works in unison, with the engine acting as the heart. This is why when the engine light comes on, many concerns can cross your mind. Drivers and car owners know that if the engine stops working, so does the vehicle and many traveling plans with it.

Fortunately, diesel compression testers are useful tools to assess the health of your vehicle. Here is everything you should know about the diesel compression testers.

Brief History of Diesel Engines

The first diesel engine prototype was created in 1893 by Rudolf Diesel. However, it was not until a few prototypes later, that Diesel was able to perfect his engine design. The second prototype completed 111 hours in testing between November and December in 1895, which was a significant success. Diesel still pushed himself to create a third prototype to perfect his design.

The diesel engine works only by compressing the air, which boosts the air temperature in the cylinder. When this comes in contact with atomized fuel, it combusts and powers the engine. This pressure is what compression testers measure to locate specific issues within an engine. There are different types of compression testers for diesel and gasoline engines.

What Are Compression Testers And When Do We Use Them

It is advised that car owners only allow mechanical engineers to fix their car engines, as it is more complicated than changing damaged tires. However, with all the information available online, many prefer to do it themselves. Compression testers allow you to measure the integrity of your engine in 30 minutes or less.

Being a car owner means there are specific things needed to keep your vehicle in the best condition possible, that regular maintenance by a mechanic will not be able to prevent. There are times when you will need to do things on your own, like refilling the coolant and replacing worn wiper blades.

Diesel compression testers are used to check the state of engine valves, its valve seats, and piston rings, and how evenly each part is eroding. Car engines have 2 valves, an intake valve and an exhaust valve, which regulates pressure within the engine.

The compression tester is to find the PSI (Pounds per Square Inch) reading, which may defer between a diesel and gasoline engine.

Here are a few steps on how to use a diesel compression tester:

  1. Disable the fuel-injection fuses by removing the fuel fuse or the entire fuel supply.
  2. Reduce compression resistance by taking out all the glow plugs.
  3. Thread the glow plug with the correct adapter from the compression tester. Make sure it is firmly attached to the glow plug hole.
  4. Disable the ignition.
  5. Use the test jumper to activate the starter then crank the engine for 4-5 revolutions.
  6. Read the PSI figure and repeat it for all cylinders.

The reading for each valve should not be more than a 10 percent difference between the lowest and highest readings. 

Look for a 100 PSI reading for each cylinder in a healthy engine. Old or rebuilt engines will naturally have a lower PSI reading than newer models. Still, it should be no lower than 75 percent. Any issues in the reading could mean there is a problem with the valves or piston coils. Take it to a mechanic if you are unable to change it yourself.

When Must You Do A Compression Test

It is best to do a compression test when your car is: 

  • slow to start
  • misfires
  • shakes while idle
  • makes puffing noises in the exhaust or induction, then it is time to do an engine compression test. 

Based on the tests, you will know if the level of compression in each cylinder. Low compression can occur in either one or both engine valves. When the pressure is lower than usual, it could mean that there is a pressure leak in the compression chamber. This is the knowledge that you may not need to know, but take it to a notable mechanic for testing.

If the valves or piston rings are worn, the engine will need overhauling. In the overhaul process, expect your car’s engine to be removed from the car, separated, cleaned, inspected for damages, then repaired and tested until it is in good condition.

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