What is the normal cylinder pressure?
3 Answers
6 megapascals, which is 6 kilograms per square centimeter. Imbalanced cylinder pressure can cause engine knocking and loss of vehicle power, and in severe cases, it can directly lead to engine failure. Cylinders can be categorized into reciprocating linear type and reciprocating swing type. Reciprocating linear cylinders are further divided into single-acting cylinders, double-acting cylinders, diaphragm cylinders, and double-impact cylinders, among others. The conditions for testing cylinder pressure are: 1. Ensure the car battery has sufficient charge during testing; 2. The engine temperature should be at a normal level, as excessively high engine temperature can increase the pressure inside the engine cylinder; 3. Remove the vehicle's fuel pump fuse when measuring cylinder pressure; 4. Remove the spark plugs when measuring cylinder pressure.
Last time I heard the mechanic at the dealership mention this, the cylinder pressure numbers are quite critical. For gasoline engines, it's normally around 8 to 12 kilograms per square centimeter, while diesel engines run higher, reaching 20 to 35. If you're driving a naturally aspirated engine and the pressure is low, it could be due to worn piston rings or valve leakage - just like my old car that felt sluggish at high speeds. A test showed cylinder pressure at only 7, and sure enough, the valve seal was cracked. Cold and hot engine tests give different readings too, usually about 0.5 lower when hot. Standards vary by vehicle model - mechanics use a special pressure gauge inserted into the spark plug hole to measure, then check that cylinder readings don't differ by more than 10%. Regular maintenance like changing air filters and engine oil helps prevent carbon buildup that can cause cylinder scoring.
I just had a major service done on my car and specifically asked about cylinder compression. The mechanic said it's like a human blood pressure reading - if the numbers are low, the engine loses power. For regular sedans, cylinder compression is typically around 9 to 10 kg/cm², with turbocharged engines being slightly higher. If it drops below 7, it usually indicates leaking piston rings or poorly sealing valves, requiring cylinder head removal for inspection. I watched him screw a threaded pressure gauge into the spark plug hole and start the engine to measure the pressure. He mentioned cold engine readings might be slightly high and recommended testing immediately after shutting off a warmed-up engine for more accurate results. Additionally, if the compression difference between cylinders exceeds 0.8 kg/cm², there's a problem. In my case, the third cylinder was 0.5 lower due to worn piston rings, which was finally resolved by replacing them with improved versions.
