Compression Check: Testing and Inspection

1. Check engine oil level and ensure starter motor and battery are all in normal operating condition.
2. Start engine and wait until engine coolant temperature reaches 176°F-0.05°F.
3. Stop engine and disconnect spark plug cables.
4. Remove spark plugs.
5. Crank engine to remove any foreign objects in cylinders.
6. Attach compression gauge to spark plug hole.
7. Depress accelerator pedal to fully open throttle.
8. Crank engine and read gauge.
9. Standard pressure is 171 psi.
10. Repeat compression check on all cylinders. Maximum difference between cylinders is 14 psi.
11. If a cylinder's compression or pressure differential is below specification, add small amount of oil through spark plug hole and repeat compression check. Causes of low compression may be as follows:
a. If addition of oil brings compression up, there may be wear between piston ring and cylinder wall.
b. If compression remains same, valve seizure, poor valve seating or a compression leak from cylinder head gasket are all possible causes.