What Causes an Engine to Lose Compression?

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What Causes an Engine to Lose Compression

Has your car engine been having a misfire or has failed to start? It could be as a result of low or no compression. If you just bought a car, it could be tricky to understand. Here is the explanation. The combustion process that comes as a result of good cylinder compression in the engine provides power making the engine operate effectively. If the compression lowers, power will also go low. As a result, you will experience engine misfire, or it will fail to work.

If you’re wondering whether driving with low compression in one cylinder is safe, note this. If the compression is low in one cylinder, your engine will start running rough. If the engine is idle, it will be stalling. It makes it worse in case you drive in heavy traffic. If you don’t have the engine inspected immediately, it could suffer further damage.

That’s why it’s vital to have your car serviced regularly. The engine oil requires to be changed at the right time to avoid piston ring wear out, which is a significant cause of low compression. Unless your engine suffers a mechanical failure, its compression usually lasts between 200,000-300,000 miles.

How to Identify The Problem

There are several low compression engine symptoms you need to watch out. Some of the symptoms include low power, poor fuel economy, and engine running rough, excessive blow-by, or even white smoke from your exhaust. If you notice any sign, you need to find out what is causing the compression.

Causes of Low Compression

Worn Piston/Rings

Worn out piston or rings is one of the primary reasons why the compression lowers. The pistons are durable and able to withstand high engine temperature thanks to their aluminum alloy. Unfortunately, with time, they get some hotspots that burn holes on your piston. The holes allow the air to leak out from the crankcase to the compression cylinder causing low compression. You can test if the problem is the piston by pouring some engine oil into your spark plugs. Check how the compression rises.

Wrong Camshaft Timing

In between your car’s crankshaft and the camshaft, there is a chain/belt. Their work is to control exhaust gas outflow from your combustion chambers. Once the belt becomes faulty, they cause camshaft not perform its task. As a result, the exhaust gasses accumulate in your combustion chambers, resulting in low compression problems.

Worn Out Head Gasket

Usually, oil and fuel are not supposed to mix in your combustion chamber. Unfortunately, an overused gasket can become cranked and allow pressure to leak from the chambers, thus causing low compression. If you suspect the problem is from the gasket, use a pressure tester. It will help you to read the pressure in your cylinder.

Faulty Valves/Valve Seats

Before releasing the combustion pressure into the exhaust, the valve first seals it. If the valve or valve seat starts leaking, it allows the compression to leak into the exhaust or even the intake. As a result, it causes low compression issues. Whether the air is leaking through the exhaust pipe or the inlet manifold, a leak-down tester can help you to identify that. Once you know where the problem is, replace the valve and also fix the seats.

Cranked Cylinder Walls

For efficient air/fuel combustion, the combustion cylinder must be tight. Unfortunately, high temperatures make the wall of some cylinders crack, resulting in low compression. If you notice some bubbles in the radiator, know that the wall of the cylinder has a crack.

Cleaned Cylinder Wall

The petrol usually washes your car oil from the cylinder wall, if your car runs without combustion for a while in one cylinder. It causes lower compression on that cylinder. To know if the problem is in the cleaned cylinder wall, pour some oil in that cylinder that has a problem. Check if the compression is improving or not.

How to Fix The Problem

Do you know how to fix low compression in one cylinder? Remember the car could have other problems. So before you take any action, you need to know that low compression is the issue. You can verify that by using a compression gauge. For the gauge to help you know if the compression is low not, it will take at least 45 minutes.

Maybe you have never used a compression gauge before or don’t have one. You should take the car to the auto repair shop near you. They will perform a compression test on your behalf and know where low compression is the problem.

If, after testing, you notice that low compression is not the problem, take the car to the mechanic. He should check the engine since a vital component in it could have some damages.

If the car has compression issues, inspect the pistons, the gaskets, not to forget the valve and the cylinder. In case they are worn out, you need to replace them right away. Since replacing them requires significant time, the cost could be high.

There are instances where there is a low compression on all the cylinders. You can identify the problem by checking both the timing belt and also the chain. If it’s in one cylinder, you need to pour oil on that particular cylinder and see if there is any improvement. In case the pressure rises, then the problem could be the worn-out piston /rings or cleaned cylinder wall. If you can’t fix the problem, replace the affected parts.


If you notice that your car has low compression, you need to have the mechanic inspect it and repair/replace the affected part. If you know how to repair it, you need to be entirely sure that the problem is about low compression. Remember, your car’s engine could have other issues causing a misfire or making it not start. You can test if compression is the issue by using a compression gauge. If you don’t have it, let the mechanic inspect and tell you what the problem is. The cost could be high since the mechanic will take a long to replace the affected parts.

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