5 Causes of Low Engine Compression
An internal combustion engine needs four things to run: air, fuel, spark, and compression. If compression is too low in any cylinder, your vehicle will not be able to run properly. Without compression in all cylinders, your car will not be able to start at all. What is engine compression?
An internal combustion engine has many pistons connected to a crankshaft. As the crankshaft rotates, these pistons move up and down through different stages of the combustion cycle. This allows the engine to deliver a steady, consistent power.
After the intake stroke, the intake and exhaust valves are closed, effectively sealing off the combustion chamber. Engine compression is the pressure that builds up in the combustion chamber as the piston moves upward. The volume of the combustion chamber shrinks from its maximum volume at bottom dead center (BDC) to its minimum volume at top dead center (TDC).
The 5 Most Common Causes of Engine Compression Loss
Below are the 5 most common reasons for low engine compression.
1) Faulty Timing Belt or Chain
The timing belt or chain ensures that the valves open and close at precise times in conjunction with the movement of the crankshaft.
A bad or loose timing belt or chain will prevent the camshaft from opening and closing the intake and exhaust valves as intended. If the timing is too off, you will experience low or no compression and your engine will not start.
2) Piston Damage
Engine cylinders contain pistons made from strong low carbon steel or aluminum alloys. These materials are designed to withstand the extreme pressure and reciprocating motion that the pistons undergo as they go up and down thousands of times per minute.
3) Piston Ring Damage
A lack of oil can quickly damage the piston rings or even the cylinder walls, causing an imperfect seal.
4) Not Correct Valve Installed
Every cylinder in an engine has an intake valve and an exhaust valve. After they mix, the combustion process occurs and exhaust gases exit the valve.
This can happen for a variety of reasons, including carbon buildup around the valve seats, bent valves, worn valve guide seals, or other damage to the valves themselves. 5) Bad Head Gasket
Carbon buildup on the wall of cylinder number 4 on this Subaru engine (right) is a classic sign of a leaking head gasket. The cylinder head gasket is located in the cylinder head area. A failed head gasket can create more places for burnt gases to exit the combustion chamber.
Does the engine run at low compression?
Car is Hard to Start
Low compression can cause problems starting your vehicle.
How to Check Engine Compression
If you suspect your engine compression is low, you should check it with a compression gauge. These meters are relatively inexpensive, and you can perform this test yourself in about an hour if necessary. If you would prefer, it will cost you between $150 and $250 to have a repair shop perform the compression test.
Remove the spark plugs for each cylinder and screw a compression gauge into the spark plug holes. Check the compression gauge immediately after cranking.
Don’t forget this step to avoid accidentally flooding the engine. It’s best to consult your manufacturer’s service manual to learn this procedure and others specific to your vehicle.