What Is the Right Operating Temperature ?

[David M]

Have you checked with Yanmar to find out the temperature range?

140F to 155F is too low for any Diesel. What's normal for most diesels is 170-180.

The first thing I would do is change out the thermostat...they can go bad.

The damage can occur in not letting the engine to get hot enough to burn the carbon out of the combustion chambers. Engines that run up to their design temperature are also more efficient.

You want to run Diesels up to their higher RPM's and put under a load.....they will last longer. Going easy on them by keeping the RPM's low all the time will actually shorten their life. I know this sounds counter-intuitive but it is true for Diesels.

Frequent oil changes are the other key to longevity

[Alecadi]

the engine is the original one: 3HMF serial number 80 from 1984. It's so far flawless (touching wood) .
I'm surprised by some comments as I have never been able to go over 2200rpm at full throtle and at those rpm anyway I'm already at hull speed since a while.... it's more around 1500 to be at full hull speed.
So when some are saying that "long term" running at below 2,500 RPM is death to a Yanmar..." I'm a little confused...
Alec

[Mark Johnson]

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.

Cheers,

Jim

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
2 GM-20-F.

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.

Mark

[Mark Johnson]

Originally Posted by Alecadi

the engine is the original one: 3HMF serial number 80 from 1984. It's so far flawless (touching wood) .
I'm surprised by some comments as I have never been able to go over 2200rpm at full throtle and at those rpm anyway I'm already at hull speed since a while.... it's more around 1500 to be at full hull speed.
So when some are saying that "long term" running at below 2,500 RPM is death to a Yanmar..." I'm a little confused...
Alec

First off, I used a poor choice of words when I said low RPMs were "death to a Yanmar". I should've said "low RPMs lead to a much shorter life". It may still work a long time. It is amazing how long they do last. I have heard of guys that NEVER changed the oil! They still got 10 years out of it, but would've gotten 20, IF they had changed the oil.

If under full throttle, your engine can't reach 3,600 RPM, (Assuming that's the listed momentary max RPM), You are over propped. The continuous RPMs and max RPMs are listed in your owners manual. It should be capable of the max!

If your momentary motoring test is within 200 RPM of the Max, most mechanics consider this good enough. It's not etched in stone.

IF your engine can reach no more than 2,200 RPM, however, you are drastically over propped, or something is wrong with the engine!

The fact that it has worked this way for 25 years, doesn't change the fact that it is damaging the engine. Perhaps now, it's a moot point?

Like I said previously, I have no opinion about this personally. When I installed our engine 15 years ago, I had long conversations with all of the Yanmar authorities I could get, like Yanmar America reps, or Mac Boring, certified Yanmar mechanics, etc. (perhaps 15 sources) Without exception, they all agree with the gist of what I have been passing on.

It seemed so counter intuitive that faster, (to a point), is better than slower RPMs, that it took me years to believe it myself.

Call 20 "knowledgeable" Yanmar reps, (not salesmen or secretaries), from far different areas and look for their consensus of opinion. THAT'S what matters, not what folks on a blog including me, have to say.

I was just passing on what I was told... "Don't shoot the messenger", please.

Mark

[delmarrey]

A quick breeze thru the PDF manuals I provided earlier, I could not find anything on RPM's except the tag on the first page of the manual (3400 RPM).

But there was a section on water temp in the second section, second to last page.

[Alecadi]

Today (Sunday) we went out and I take the opportunity to push the engine .

Under 2000 the temp stabilizes around 150 F
When pushing to max throttle (2500 rpm) it reaches 170+ and stabilizes there. I stay at this speed for about 30mn.
When getting down rpm the temp get back to 150- 155

By the way full throttle is only 2500 rpm and the boat is at 7.4 knts at 2200 rpm and this is max hull speed or very near.. there is no way to get more rpm (anyway to what purpose as the boat cannot get quicker??)

And oil pressure is perfect at all rpm and very stable

I don't see a problem there . Or I don't get the point yet. And it has worked like that since 1984.. which make almost 30 years!

For me it's normal to get less temp at less rev. Perhaps I'm wrong.
But based on my (already) long experience with racing car, and airplanes, it's always like that : less rev less temp, more rev more temp.
When the engine starts to get higher temp the first recommendation is to ease on the throttle to give it a break.

I don't see why marine engine should be different.

I'll be glad to have your opinion on this.

Some are saying it's overpropped... ??? it get to full speed very quickly and with no problem, no cavitation, the prop, shaft, and transmission are all original. And the boat has been very well maintained by the previous owner (same people since new, I'm the second owner since last june)

Alec

[delmarrey]

Originally Posted by Alecadi

Today (Sunday) we went out and I take the opportunity to push the engine .

Under 2000 the temp stabilizes around 150 F
When pushing to max throttle (2500 rpm) it reaches 170+ and stabilizes there. I stay at this speed for about 30mn.
When getting down rpm the temp get back to 150- 155

By the way full throttle is only 2500 rpm and the boat is at 7.4 knts at 2200 rpm and this is max hull speed or very near.. there is no way to get more rpm (anyway to what purpose as the boat cannot get quicker??)

And oil pressure is perfect at all rpm and very stable

I don't see a problem there . Or I don't get the point yet. And it has worked like that since 1984.. which make almost 30 years!

For me it's normal to get less temp at less rev. Perhaps I'm wrong.
But based on my (already) long experience with racing car, and airplanes, it's always like that : less rev less temp, more rev more temp.
When the engine starts to get higher temp the first recommendation is to ease on the throttle to give it a break.

I don't see why marine engine should be different.

I'll be glad to have your opinion on this.

Some are saying it's overpropped... ??? it get to full speed very quickly and with no problem, no cavitation, the prop, shaft, and transmission are all original. And the boat has been very well maintained by the previous owner (same people since new, I'm the second owner since last june)

Alec

Did it put out any black smoke at full speed and or do you have soot around the exhaust outlet. If not, I wouldn't worry too much. Your tachometer could be off, or your timing pump could need adjustment.

If the motor is over worked it will start to smoke. If under worked it'll glaze the cylinder walls. Diesels can be a blessing or a burden, depending on how they're used.

The temps do seem to be on the low side though.

[Alecadi]

Delmarrey: Thank you so much for your help
The owners manual that you referred to me indicate for the 3HMF: 30HP at 3400 rpm, thermostat valve opening at 159 F and normal operating temp at 3400 rpm : 185 F
No smoke.
For what I can see of the boat since I got her last June the previous owner was very meticulous.. so I'm quite sure the engine has been "well treated".. :-)