A marine engine survey is a detailed inspection of a boat's engines by a mechanic who knows that make: oil analysis, a compression test, a run under load with temperatures measured, and a report on what was found. It's usually separate from the hull survey. The late surveyor David Pascoe wrote that most surveyors don't perform diesel engine surveys, and recommended a full one on older and larger engines.
Why the engines get their own survey
Money. Engines are often the most expensive single system on a powerboat, and Pascoe noted that repairs on diesels typically cost four times those on gas engines. A general survey sees what's on the outside: leaks, corrosion, belts, hoses, mounts, the exhaust elbow. An engine survey looks for wear you can't see.
BoatUS advises hiring a mechanic trained in that particular type of engine. Steve D'Antonio, writing in Cruising World, prefers one employed by a dealer for that make. Yachting Monthly adds that a dealer's engineer may have software to plug in, which reads the engine's own records.
What an engine survey includes
Oil and fluid analysis
A sample of engine oil, and often gear oil and coolant, goes to a lab. BoatUS says the oil is analysed for metals, water and mineral deposits, and only specialised labs can do it. D'Antonio says the value of fluid analysis "can't be overstated", with kits costing about $30 each. Pascoe found its main benefit was catching salt, water or antifreeze in the oil, and that results usually took about three days, so they arrive after the survey day.
Compression test
BoatUS describes it as showing whether seals need replacing or there are problems with cylinders and pistons. D'Antonio recommends it on any used engine. Pascoe offered it on gas engines as an extra, particularly on engines four years or older. Read the results across cylinders: an even spread matters more than the absolute number. The compression test results tool works out the spread.
The run under load
The engine is run hard, with readings taken. D'Antonio's test:
- at least one hour under way at 80 percent of maximum rpm, and 10 minutes at full throttle;
- reaching the maker's rated rpm at full throttle;
- exposed dry exhaust no hotter than 200°F (93°C), water-cooled exhaust typically no more than 150°F (66°C);
- the engine compartment no more than 30°F (17°C) above the cabin air;
- exhaust back pressure measured against the maker's limit.
Watch for smoke colour, oil pressure, coolant temperature, vibration and anything that changes as the engine warms up. See engine overheating.
History and hours
Hours tell you where the engine is in its life. The boat engine hours page sets out what's high for diesel, gas and outboard engines. Service records, oil change intervals and any rebuilds matter as much as the number. For known faults by make, see known engine problems.
What it costs
BoatUS puts an engine survey at about $500 per engine. Oil analysis is often a separate charge per engine. On a twin-engine boat with a generator, you're paying for three surveys, plus the lab.
Against what it protects, it's cheap. A failed compression test or salt in the oil changes the price of the boat by far more than the fee. See boat survey cost.
Engine survey checklist
Before the run
- Engine make, model, serial number and hours, from the hour meter and the engine's own records
- Service records and the date of the last oil change
- Mounts, beds, alignment and the shaft coupling; see failed engine mounts
- Leaks: oil, fuel, coolant, raw water; see raw water pump leak
- Belts, hoses, clamps, heat exchanger, exhaust elbow and exhaust hose
- Fuel filters and water separators, and the fuel in them; see diesel bug
- Oil and coolant samples taken before the run
Running
- Cold start: how it starts, smoke, oil pressure rising
- One hour at 80 percent rpm and 10 minutes at full throttle
- Exhaust, engine room and coolant temperatures against the limits above
- Rated rpm reached at full throttle
- Gearbox engagement, ahead and astern
After
- Compression test, or the reason it wasn't done
- Lab results when they arrive, added to the report
The engine survey report template gives the layout for writing it up, with a free Word download.
For surveyors: write the engine findings as you go
An engine survey produces a lot of numbers: hours, pressures, temperatures, compression per cylinder. With Axsail you say them out loud as you read them, and they land in the findings with their units. If you skip one, the app asks for it while you're still in the engine room. The lab results get added on the web when they arrive. See how it works.