Originally Posted by Jim Cate
If this is really true, one wonders why Yanmars have a good rep in the sailing world. Seems to me to cross that marque off my potential buy list. Anything that finicky doesn't belong on a cruising boat IMO.
The statement that I made was not just my experience, or that of 100 people on a blog, based on their anecdotal evidence. The admonition to run them at the higher RPMs that they were designed to be run at, comes from the manufacturer's decades of testing, as well as the feedback from tens of thousands of customers.
Importers, distributors, and certified Yanmar mechanics, all pretty much agree on this point: "IF you want the longest life and least hassle over many years, run one like mine, (which has a Max RPM of 3,600 and a Max "crusing" RPM of 3,400 RPM)... at between 2,600 RPM and 2,900 RPM, (IF on an all day basis)."
If circumstances don't allow this speed, every hour rev it up to well over 3,000 RPM, for 5 minutes or so to blow the carbon out.
I don't have an opinion about this personally, because I haven't run several engines to the rebuild
point at low RPMs, and then done the same to several engines at high RPMs. Then make a useful engine life comparison.
Since the above test would take a lifetime, I just fall back on what the engineers, manufacturers, importers, distributors, and certified mechanics for Yanmar say. Their opinion is more valid than mine.
If one wants a big screw going slow, rather than a small screw going fast, and the RPM band doesn't work out for their needs, several transmissions are available to get the shaft RPM that you need.
If you need to run your engine at anchor
to charge your batteries, having it in reverse with a bit of RPS is better than idle, but this is in fact the most damaging hours that you will ever put on your engine. It may still last 10 years, but might have made it to 20 otherwise. (A good solar
array would be cheaper).
I asked a Yanmar mechanic
once, just back from Yanmar school
, how they came up with the 3,400 RPM as a potential continuous "cruising max RPM". (No one really does this, for fuel consumption
& mileage efficiency reasons). His answer, however, was interesting. It seams that they hook up an engine on a test bench with fluid changing plumbing
. This allows continuous running without shut down! They then run the test engine @ 3,400 RPM, 24/7, for a continuous year. NON STOP! This represents a lifetime of running for my
These numbers are not guesses, they are based on decades of scientific testing, as well as anecdotal evidence from hundreds of thousands of customers all over the world.
It could be the number of dealers & mechanics, the reasonable price
, light weight, reliability
, or availability of parts
, that has made Yanmar one of the most popular marine
engines in the world. I have no idea. But most folks are pleased with them.
If someone doesn't like the modern, light weight, high RPM engines, then they can go with the older low RPM type, (like a Perkins), and run them at low RPMs all their life. They are designed for low RPMs and will hold up fine this way.
It is all about what you want... A small, light weight, high RPM engine, or a huge / heavy, low RPM engine. They both work great, if run within their own parameters.