Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSFORD2021TRANSIT-350 HD BASE, VAN CARGO EXTENDED, 3.5L ENG VIN 8, AWDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 620 (ENGINE SYSTEM - GENERAL INFORMATION)GENERAL PROCEDURESCOMPRESSION AND CYLINDER LEAKAGE TEST - GASOLINECOMPRESSION TEST - INTERPRETING COMPRESSION READINGS
2021 Ford Transit-350 HD Base, Van Cargo Extended, 3.5L Eng VIN 8, AWD
Compression Test - Interpreting Compression Readings
2021 Ford Transit-350 HD Base, Van Cargo Extended, 3.5L Eng VIN 8, AWDSECTION Compression Test - Interpreting Compression Readings
WARNING: This page is about a different car, the 2021 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.
- If one or more cylinders reads low, squirt approximately one tablespoon of engine oil meeting Ford specification on top of the pistons in the low-reading cylinders. Repeat the compression pressure check on these cylinders.
- If compression improves considerably, piston rings are worn or damaged.
- If compression does not improve, valves are sticking or not seating correctly.
- 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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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.