What is the normal cylinder pressure for a 4-cylinder car?
2 Answers
Normal cylinder pressure for a four-cylinder engine should not be lower than 7 bars. The cylinder pressure also varies depending on the vehicle series. Japanese cars generally have a cylinder pressure of 1100 KPa (approximately 10 bars), while European and American cars typically range between 1200-1300 KPa (approximately 12-13 bars). The following are reasons for insufficient cylinder pressure: 1. Cooling system leakage leading to water shortage, causing the engine to overheat. 2. Piston ring breakage, piston pin retainer detachment, or piston pin protrusion, which can scrape the cylinder wall. 3. Piston rings stuck in the ring groove due to excessive carbon buildup, losing their sealing effect. 4. Foreign objects entering the cylinder.
The normal compression range for a 4-cylinder car is generally between 100 to 150 psi, which converts to approximately 700 to 1000 kPa in metric units. I've worked on many engines during repairs, and the pressure difference between cylinders shouldn't exceed 10%, otherwise the engine will shake noticeably. Low compression is usually caused by worn piston rings or valve sealing issues. Over time, this leads to increased fuel consumption and reduced power, so early detection and repair are crucial. New cars may have slightly higher compression, while older cars tend to be lower, but anything below 90 psi indicates serious problems. It's best to perform the test when the engine is cold, using a compression gauge inserted into the spark plug hole - take it slow to avoid hand injuries. Maintaining proper cylinder compression extends engine life; I personally check mine every two years to avoid major overhauls.
