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Compression Test - Interpreting Compression Readings

  1. If compression improves considerably, piston rings are faulty.
  2. If compression does not improve, valves are sticking or seating incorrectly.
  3. If two 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 in Figure when checking cylinder compression so that the lowest reading is at least 75 percent of the highest reading.

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