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Compression Test - Interpreting Compression Readings

WARNING: This page is about a different car, the 2018 Ford F-550 Super Duty, 2018 Ford F-450 Super Duty, 2018 Ford F-350 Super Duty, and 2018 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
  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 the lowest reading is within 75% of the highest reading.
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