Ranger 4WD V6-3.0L VIN U (1997)
Compression Check: Testing and Inspection
Interpreting Compression Readings
It is recommended the Compression Pressure Limit Chart be used when checking cylinder compression so that the lowest reading number is 75 percent
of the highest reading.
If one or more cylinders reads low, squirt approximately one tablespoon of SAE 50 weight or equivalent engine oil on top of the pistons in the low
reading cylinders. Repeat compression pressure check on these cylinders.
1. If compression improves considerably, piston rings are at fault.
2. If compression does not improve, valves are sticking or seating poorly.
3. If two adjacent cylinders indicate low compression pressures and squirting oil on pistons does not increase compression cause may be a head
gasket leak between cylinders. Engine oil and /or coolant in cylinders could result from this problem.
If, after checking the compression pressures in all cylinders, it was found that the highest reading obtained was 1351 kPa (196 psi)and the lowest
pressure reading was 1069 kPa (155 psi), the engine is within specification and the compression is considered satisfactory.
