There are many possible causes of engine failure. You can see our earlier post on diagnosing engine failures, too.
One common cause of engine failure is low or no compression in your cylinders. Diesel engine compression issues have several potential causes, so you’ll need to narrow it down by diagnosing the symptoms. We’ll cover some of the causes of compression failure. If you want help finding the root cause, refer to your manufacturer’s specifications or a trusted mechanic.
Indicators of Diesel Compression Issues
Low compression symptoms are very similar to fuel contamination symptoms: for example, low power and suffering fuel economy. You may also notice your engine running more roughly, excessive blow-by, or white smoke coming from your exhaust. If you notice any of these symptoms, you should run a compression test to see if low/no compression is the root cause. Depending on which components are affected, you may need an engine rebuild to eliminate compression problems.
Mechanic’s note: Engine blow-by is when a mixture of combustion gases, air, or fuel leaks from the engine’s pistons and cylinder wall into the crankcase. It can happen in both diesel and gas engines.
What is good diesel compression?
Good compression for a diesel engine falls from 275 to 400 psi. Typically, you don’t want variances of more than 10% between cylinders.
Causes of Low or No Compression
Poor compression is often a symptom of larger-scope engine problems. There are many other engine issues that can affect compression:
- Leaking or Broken Valves: This allows the compression to escape the cylinder where the issue is located.
- Leaking or Worn Piston Rings: When these rings wear or fail, compression can leak from the cylinder heads.
- Broken Valve Spring: A broken valve spring allows the valve to stay open, which lets the compression leak out as well.
- Blown Head Gasket: This creates a poor sealing surface, which can allow compression to leak from one or more cylinders, depending on the extent of the damage.
- Worn or Broken Camshaft: Issues with your camshaft prevent the valves from opening the proper amount, which doesn’t allow for air and gases to enter and exit the cylinder.
- Broken Timing Belt or Chain: If this isn’t working properly, then the camshaft isn’t rotating at a proper speed, preventing compression from taking place as it should.
- Hole in Piston: A hole in the piston would again allow for compression to leak out.
Monitoring and Identifying Diesel Engine Compression Issues
All of your engine cylinders are prone to low compression symptoms. Running a compression test will help you identify where the issue lies; it also helps narrow down any possible causes. For example, one of the cylinders might have a broken valve affecting it.
Low Compression in One Cylinder
Common symptoms of low compression that only affect one cylinder include leaking valves, broken valve springs, camshaft wear, broken rings, or a bad head gasket.
Low Compression in All Cylinders
If your test shows low compression in all cylinders, it may be engine flooding, worn piston rings, cylinder glazing, poor air filtration or dusting, or timing problems.
No Compression in One Cylinder
If a cylinder has no compression, it might indicate a dropped valve seat, broken valve spring, dropped valve, broken valve, or piston damage.
No Compression in All Cylinders
If none of your cylinders have compression, it might be a broken camshaft.
Compression tests help you narrow down the issue. A compression test also tracks your engine performance as frequently as you want. You can see how your cylinders are doing compared to each other. This lets you isolate the problem and helps you determine where it’s located: one cylinder, two cylinders, or maybe all.
Compression tests are run through the glow plug holes or injector holes. Where they plug in depends on the engine specifications and the type of gauge you’re using. For more information on your engine type, you should refer to the manufacturer’s instructions.
If you think compression issues are causing further engine problems, you may need an engine rebuild. If that’s the case, make sure you get a high-quality diesel engine rebuild kit from a reputable retailer. Contact us at 833.990.3406 if you need help determining what you need for your diesel engine.
FAQS About Diesel Engine Compression Issues
1. What are the common signs of low compression in a diesel engine?
Common indicators of low compression include:
- Difficulty starting the engine
- Reduced engine power
- Excessive exhaust smoke
- Rough idling
- Increased fuel consumption
- Excessive blow-by
These symptoms can resemble those of fuel contamination, so it’s essential to perform a compression test to determine the root cause.
2. What is considered a good compression reading for a diesel engine?
A healthy diesel engine typically has compression readings between 275 to 400 psi, with no more than a 10% variance between cylinders.
3. What causes low or no compression in diesel engines?
Several factors can lead to low or no compression:(CARiD)
- Leaking or broken valves
- Worn or damaged piston rings
- Broken valve springs
- Blown head gasket
- Worn or broken camshaft
- Broken timing belt or chain
- Holes in pistons(ATL Diesel, CARiD, My Bubba and Me)
Identifying the specific cause requires a thorough inspection and testing.
4. How can I test for compression issues in my diesel engine?
To diagnose compression problems:
- Remove the glow plugs or fuel injectors.
- Insert a diesel compression tester into the cylinder.
- Crank the engine and record the pressure reading.
- Repeat for each cylinder.
Compare the readings to the manufacturer specifications to identify any discrepancies. (dieseldoctor.ca)
5. What should I do if I find low compression in one or all cylinders?
- One cylinder: This may indicate issues like a leaking valve, a broken valve spring, or damaged piston rings.
- All cylinders: This could suggest problems such as a blown head gasket, worn camshaft, or timing belt/chain failure.
