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Compression Test - Interpreting Compression Readings

  1. If compression improves considerably, piston rings are worn or damaged.
  2. If compression does not improve, valves are sticking or not seating correctly.
  3. If 2 adjacent cylinders indicate low compression pressures and squirting oil on each piston does not increase compression, the head gasket may be leaking between cylinders. Engine oil or coolant in cylinders could result from this condition.

    Use the Compression Pressure Limit Chart when checking cylinder compression so that the lowest reading is within 75% of the highest reading.

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