Used Boat Engine Checks

When you buy a used boat, you want to make sure that the engine is good (unless you are buying a salvaged vessel) or want to install replacement engines. Inboard diesel engines are generally reliable. So how do we find out if the engine is good? Ultimately, you have to sea-test the boat you are buying, but there are several basic engine checks you can make on first pass. I can't offer advice on buying big outboard petrol/gas engines as they are not my field.

If the boat is ashore and you want to run the engine (you'll have to try it sometime), then a cooling water supply will have to be set up (if the boat has keel cooling then this other ways will have to be found). This can be done with a hose pipe, but make sure that the seller (or his agent) agrees to this, and get them to do it. OK, so we have a cooling system ready.

1. Does the engine look clean and well-maintained? An owner who cares will have a clean and well painted engine, so that any oil or water leaks are immediately visible. If the engine looks dirty, then be on your guard.
2. Check the lub oil – is it clean and is the level up to the full mark?
3. Are there signs of water in the lub oil?
4. If you can, check the transmission oil – level and colour – grey or milky means there’s water in it.
5. Does (Do) the engine(s) have an hours meter? Check the hours meter. Yes, they can be faked or replaced, but most owners are genuine. As a guide, a really good truck engine which is really well looked after will do a million miles without a problem. At an average speed of thirty miles per hour, say, that’s more than thirty thousand hours.
6. Start the engine. Immediately check that there is a flow of cooling water. It's hard to judge volumes, but a diesel engine needs about 20 gallons/minute (80 litres) per minute of cooling water at about 20 Deg C (60 deg F) per 100 hp to stay at the right temperature. So, a 50 hp engine at working temperature and full power will need about 10 gallons/ minute. Lots of things can affect this - broken pump impeller vanes, blocked or scaled heat exchangers, slipping pump drive belts just to name a few. 
7. Did the engine start easily? Obvious, but if it didn't you may be told that the battery is flat. It shouldn’t be flat if the seller wants to make a sale. It could mean that the starter motor is faulty, or cables / terminals are in poor condition.
8. Is there a lot of blue smoke when the engine first starts? If there is, then this could indicate, for example, that the valve guides are worn, or cylinders/piston rings are worn. With diesels, some blue smoke is inevitable, but it should not be like a thick fog.
9. Check that the alternator is charging properly – the charge light should be out and the ammeter should be showing charging current. The 'ignition' warble siren/whistle should have stopped immediately the engine started. If shore power and a charger is switched on, then the whistle may not stop until the shore power is switched off.  Continued..

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