The question about harming a diesel
engine by running at low speed gets debated on this and other boating forums
First lets separate wear from glazing and carbon build up. Wear results from several factors: rpm, bmep (brake mean effective pressure, a measure of load), temperature, lube oil
age and oil
pressure. So running at high rpm at wot in gear
with a fouled cooling
system, a bad lube oil pump and with old oil will lead to a lot of wear.
gurus on boatdiesel (marine diesel shop owners and engine developers) generally agree that running a diesel at low load, as long as it reaches operating termperatures, will do no long term harm. It generally takes about 30-40% of wot rpm to put enough load in gear
on a marine
diesel to keep it up to operating temperatures. For the typical small Yanmar in sailboats that is about 1200-1500 rpm.
Since sailboats operate at displacement
speeds and their engines are often sized to push them up to hull speed
plus a small margin for adverse waves, we usually operate at about 80% of hull speed
. That is an efficient and comfortable speed and typically is at about half of the engines rated horsepower and 75% of maximum rated rpm. But running at 1/3 of rated rpm won't hurt them although it will be pretty slow.
I have had the injectors on my small Yanmar foul up. Running the engine hard at 3000+ rpm cleans them up. I have cruised for hundreds of hours at 2,400 rpm. If I run it up to 3000+ every hundred hours or so it blows out any accumulated soot and cleans up the injectors.
Finally I don't buy the argument that diesel engine rings NEED high combustion chamber pressures to seal them to the cylinder walls otherwise they will allow combustion gasses to blow by. There is a simple way to check for blow by. Put your finger next to the outlet of the small hose that comes from the valve cover on your Yanmar and most diesels. Feel for blowby pulses. Rev the engine in neutral (ie light load) up and feel for any pulse. Good engines with good compression
will not show any blowby. Sure worn rings will produce blowby but it doesn't decrease when you put the engine in gear and put a load on it.