I wrote (to add further info that I've thought of since): snipped: > Firstly, you are correct that designing a boat with a huge engine, > well in excess of your real needs, will tend to exacerbate the > problem because you are running it so lightly loaded. So, stick to an > engine as small as you can reasonably get away with.....but remember > to allow for those emergency situations where you find yourself > punching a tide, maybe. There's only one engine worse than a bore- > glazed one and that's an engine that's overheated, or worse still > blown up, because you've been forced to flog it hard for hours on > end. And, of course, this will almost certainly happen on a tidal > waterway where it is less than convenient (master of understatement) > to be left with no power > ;-)))
Also, make sure your boat builder correctly specs the skin cooling tank size for the size of engine. It's no good having a large engine flogging away on a tidal stretch and doing quite nicely when you discover that it's overheating due to an inadequate skin tank area and you have to throttle back to preserve the engine..........you might as well have a small engine in that case. ;-)) > > Secondly, modern engines are more likely to be affected due to the > fact that they use highly sophisticated lubricants with lots of > additives. If they were running on older grades of lubricants you > would probably not get the problem, however the warranty conditions > will preclude oil grades below a certain level. So use the lowest > grade of oil that the manufacturer will allow (probably API CF or > CG, or even higher by now, CF being a lower spec than CG) I believe that some engines are filled with a running-in oil from new to help them bed in and prevent bore glazing. Such a product is Morris's Ambesta Running In Oil. All it is really is a fairly simple, old fashioned oil with negligible additives thus allowing the rings and bore surfaces to really abrade against each other for the first few tens of hours. Although it probably wouldn't be recommended, I wouldn't be surprised if you could do an oil change with this oil if you suspected that your engine was starting to bore glaze and, as long as you didn't run it for hundreds of hours, run the engine fairly heavily before swapping back to a more sophisticated oil. Roger
