Mechanical survey and oil analysis

Why a separate engine check

A hull surveyor looks at the engine, checks for leaks and runs it. A mechanic works from the maker's manual and has the tools to read data, test pressure and take samples. For an older boat, a big engine, a twin installation or any engine that carries a lot of hours, the extra fee is cheap beside a rebuild. See Engine hours, and whether they can be trusted.

What a mechanic checks

1. Cold start. A healthy diesel starts quickly. Long cranking, white smoke that does not clear, or knocking show trouble.
2. Exhaust. Light haze is normal. Black smoke shows overloading or poor injectors. Blue smoke shows oil burning. White steam that persists shows coolant in the cylinders.
3. Leaks: oil, coolant, fuel and exhaust.
4. Cooling. The heat exchanger, the impeller, the raw-water strainer and the exhaust elbow, which corrodes inside.
5. Mounts and alignment, to find vibration at speed.
6. Gearbox and drive: engages ahead and astern smoothly, oil is clean.
7. Data. Read hours and fault codes from an electronic engine.
8. Compression or blow-by test, where the engine allows it.

Oil analysis

The mechanic draws a small sample from the warm engine and posts it to a lab. The report lists wear metals such as iron, copper and aluminium, the presence of coolant or fuel in the oil, and the oil's condition. A trend across samples tells more than one result, so ask the seller whether earlier reports exist. The cost is small compared with the information.

Under load

At the sea trial, the engine should reach its rated speed at full throttle, hold it, and stay at a steady temperature. See The sea trial checklist.

Generators and other engines

Treat the generator, the bow thruster, the tender outboard and any hydraulic pack the same way. See Electrical system and generator.

Related guides

• Engine hours, and whether they can be trusted
• The sea trial checklist
• The annual maintenance schedule and antifouling