Diesel RPM?

[Lee Jerry]

Originally Posted by massnspace

That’s correct.

Thread drift is one of the things I don’t enjoy about this forum, but I’ll take the good with the bad.

Thanks to those who have contributed towards my original question.

As far as oil analysis…..I just changed it. How long should one wait before attempting that?

David
Seattle

Actually, how you are propped could/should factor into the answer. And you never specified: is the 2500 rpm you referenced in the original post at WOT?


To reiterate, I would not run at 1500 rpm "all day." I think you're fine doing it for a few* hours, but then I'd increase to 1800 - 2000 rpm for a while (half to one hour). You could then return to 1500 and repeat.

* How long a few hours is depends on what the operating temp is at that RPM (assuming you have a coolant temp gauge). If it's reasonable then a little longer is OK, but if it's rather low then run it up more frequently. It also may change with ambient temperatures (air and water) - you might be OK in the summer, but early spring cooler waters may bring the temp down too much, for example.


Finally, have you checked your tachometer recently? IOW, is that 1500 rpm the actual speed of the engine? That could also affect the answer.

[pbiJim]

Originally Posted by boatpoker

Slight over propping is not a bad thing.

Unless you find yourself with 40+ knots on the nose & a lee shore behind you.


In those conditions, I was forced to put canvass back up to keep the boat off the shore & the only other person on board was a senior who had very little time in on sailboats. A shallower pitch prop would have been a grand improvement in my day during that squall.

[dannc]

Originally Posted by massnspace

...

As far as oil analysis…..I just changed it. How long should one wait before attempting that?

David
Seattle

I don't know how long the oil would need to be run to get a good UOA. I run up to my engine hours/miles, change the oil and send in a sample. The sample size is not large, maybe a 1/4 - 1/3 of a cup. Maybe.

Ask Blackstone and see what they say. I have found them responsive over the years.

https://www.blackstone-labs.com/contact/

[bdbcat]

mannspace...
There is another way to measure true engine load factor.
Install fuel flow meters, or take some careful measurements of volumetric consumption over time.

Your engines, my engines, everybody's diesel engines will consume about 1 gph for each 18-20 hp created. By knowing the actual power produced by the entire drivetrain, and the rated power of the engine, you can calculate the load factor.
But what load factor is acceptable, or reasonable? There you will get lots of opinions...


Anecdotally, I have 14,000 hours on a pair of Cummins BT5.9M over 24 years on my 50' aluminum power cat. Engines never cracked open. Still start on two turns, run fine all day long. For at least 90% of that time, the measured load factor was about 30%, or about 50 hp per side.



Truly, YMMV
Dave

[Kettlewell]

Another anecdote. I routinely run my Perkins 4.236 at 1500 rpm and under, including probably 1,000 hours or more of just charging at 1200 rpm. 1500 pushes my Finnsailer at about 6 knots. Redline is only 2200. Frankly, I'm not sure if I have ever reached redline. Occasionally in the ICW I have pushed up to about 7.5 knots or so, which is really pushing a huge bow wave and not something I would want to do for too long. There is still more throttle after that but I doubt it would give me much, if any, more speed. Just approaching 5,000 hours on the engine, the heads have never been off, burns less than 1gph at 1500, no smoke, starts on the first crank every time. In fact, I have to be careful not to touch the start button or it fires right off, even after sitting all winter long. I've started it by accident a few times by touching the start button.

[howardatviking]

I belive all engines are different and that must be taken into account fot example my last one used to tick over at 200 revs, cruise at 500 revs and max out at 900 revs. Perhaps a percentage of engine range might be a better guide. Any thoughts

[gulfislandfred]

If I'm not mistaken, your Universal M40 is a Kubota?
Those engines are all over the world, in many applications. Just change the oil now and then, and the engine will be happy.
Special issues due to raw water cooling or combined raw water/fresh water cooling do need attention. Exhaust elbows can clog up.
As others have said, it helps to run the engine at high enough rpm, or enough load, to get the whole system warm now and then. An hour or more is ideal, but as little as 15 minutes of high load, several times, will clean out the carbon.

[sinnerman]

Boy, this question brought out a lot of responses...

Basic reasoning I understood was that diesels like to be run under load.

If you want to cruise the boat at 1500 RPM, then since the engine is under load (actually moving the prop and pushing the boat) it is functioning as designed.

What they do not want you to do is have the engine running at idle for hours on end just to charge the batteries..

Supposedly this will "glaze" the cylinder walls.

Of course this could all be hearsay

MY two cents

Cheers...

[Wandering1]

My generator is a twin cylinder diesel Perkins. It runs at 3000rpm. The same basic engine can come in 3 cylinder variants. The three cylinder version runs at 1500rpm.
Many 3 cylinder diesels run at 1500rpm for long life and reduced noise.
MyPerkins m92B is 4.4 litre. This is my main engine. This produces 86hp and maximum torque is at 1200rpm. Maximum revs should be 2400rpm according to the handbook but we are over propped with a 22" prop. Our preferred cruising revs are 1200rpm. In flat water this gives us 6kts. We use 3.3litre/hr pushing a 19 tonne sailing boat along. It has been set up this way since 2007 when the current engine was fitted. 3000hrs later and all is good

[kenbo]

Originally Posted by Loredo

Can we please put this "ideal diesel RPM" thing put to sleep once and for all?
It is nonsense!
Also prop-match without supporting data makes no sense. Where do we get the "data" from? An Exhaust-Gas-Temperature sensor is the only answer and the only way to KNOW if an diesel engine is overloaded or not. Extremely simplified, "ideal" cruise speed EGT is in the 600 to 800 degrees Fahrenheit range. Below that and the cylinders are cold, above that for long periods and the engine will suffer in the long run. Ideally we'd need to monitor the coolant temp, the oil temp and the EGT. Only that will provide the picture about the working load on the engine. Anything else is just gossip.

I understand that most if not nearly all sailors do not have an EGT sensor but in actuality, engine rpm has only an approximate bearing on engine load. The only reliable way to KNOW how your engine is loaded is to measure EGT. The huge variability in engine designs and running gear differences make discussions about rpm almost worthless. And that takes into account is the tach accurate?

What I do know is that overloading an engine can reduce it's life. And having put diesel engines on a dyno I can tell you EGTs rise extremely fast and do not correlate with coolant temps vs. time at all.

So to the OP, I don't know if your engine is loaded properly and everyone else is guessing or extrapolating their experience with their engine.

[cottonsail]

I put in a new Volvo Penta D2-50F a few years ago. A Volvo tech came out to do the sea trials and certify the installation. During sea trials, at full throttle the engine reached 3200 RPM. The Volvo guy was quite pleased with this. He then instructed me to cruise at 27 to 2800 RPM. This seems high to me. 3/4 power should be about 2400. Following his advice we cruised at 2700. After a few hours I noticed the oil pressure drop about 2 psi. It is a 10-quart system. We now cruise about 24, 2500 RPM with no oil pressure drop. Any thoughts please.

[boatpoker]

Originally Posted by cottonsail

I put in a new Volvo Penta D2-50F a few years ago. A Volvo tech came out to do the sea trials and certify the installation. During sea trials, at full throttle the engine reached 3200 RPM. The Volvo guy was quite pleased with this. He then instructed me to cruise at 27 to 2800 RPM. This seems high to me. 3/4 power should be about 2400. Following his advice we cruised at 2700. After a few hours I noticed the oil pressure drop about 2 psi. It is a 10-quart system. We now cruise about 24, 2500 RPM with no oil pressure drop. Any thoughts please.

As oil heats up it gets thinner therefore easier to pump and lower pressure, a small pressure drop is normal when your engine heats up.

[Bill_Giles]

It does not do a diesel much good to run at low revs for long periods, especially not driving. Do vary the revs, get the engine working hard for spells to burn off carbon build up and to avoid glazed or burnished bores.

[motion30]

What's interesting is you go to a big truck stop anywhere where there's cold weather and there will be dozens of trucks at idle for hours and hours

[donradcliffe]

A couple of years ago, I delivered a boat back from Hawaii. A 75 hp turbo yamar 4jh4-te, and there was no wind so I had to motor for 200 hours at 2000 rpm. When I got close to land, I tried to run the motor up, but it wouldn't do over 2100 WOT. Wanna guess what the problem was?