Is running at lower (1500-2000) RPMs bad for the engine?

A

Aurora_WA

Member
Joined
Sep 24, 2013
Messages
23
Fluid Motion Model
C-24 C
Non-Fluid Motion Model
Cutwater 26
Vessel Name
Aurora
Hi all,

Is it safe for the engine to be running slower (i.e. 1500-2000 rpm) on a cruise? Or should I try to stay at 80% of the engine's max (i.e. 300- 3300)?

The reason I ask is that last weekend we went out in our Cutwater 26, and we were having a great time slowly motoring (~1700 rpm) to a nearby port. When we came back home, my friend (who is a boater with lots of experience) told me that it wasn't "good" to run engines at "such low" rpms (approx. 40% of max). I've looked around online, and I haven't found anything that really confirms or denies this.

What do you guys think? Is this guy's free advice worth what I paid for it?

Thanks in advance for you advice!
 
IMO, you can run any RPM you like. I would open her up occasionally to blow out any carbon build up. But I cruise at 12 knots, 2800 RPM mostly. Just keep an eye on the temp. gauge. With a diesel, that the 1st indicator that something is wrong. Again, this is just my opinion. I am not a mechanic, but I have been boating 25 yrs, 20 yrs. with a diesel engine. I did read somewhere you shouldn't "idle" for long periods of time.
Chester
 
I suggest you read your engine manual. On boats I have owned, Yanmar specified NOT to run the engine at low RPMS for extended periods. I have been told that the newer Common Rail diesels with electronic controls are more tolereant of low RPM operation. Still, the occasion run at 80 peercent of full cannot hurt.
 
Running at low RPM in the range you mentioned is not a problem, but you do want to run it up at least once on your trip to get the engine temperature up for a few of reasons, a) to exercise your turbo, b) to burn off any condensation water that may be in your oil, c) burn out any carbon build up.
 
I wonder often about best practices with rpms. The manual for our Volvo 200 D3, at page 48, says only:
For best fuel economy operations at full speed must be avoided. We recommend a cruising speed that is at least 10% below the maximum engine revolutions at top speed (full throttle).
Click to expand...
Not very enlightening. I'd really like to know how best to run our Volvo to minimize maintenance issues and maximize its lifespan more generally. Seems like better information ought to be out there, somewhere, and specific to our respective engines. But it sure seems hard to come by.
 
I have not read any Volvo engine manuals. In my Yanmar manual, the info is scattered all over the place. This is the trick I used to find the info. I opened the digital copy of the manual (on the CD), and did a search for RPM and found all the info I wanted, including break-in, slow cruise, fast cruise, max rpm, idle, etc.
 
Rick, a resourceful suggestion! After reading your post, I tried searching through the Volvo manual that way (using rpm as well as the other terms you listed). Unfortunately, I found nothing other than the one bit I quoted in the earlier post. But I did end up refreshing my memory on a few things that, over the winter, I had forgotten about. So it was a worthwhile effort, even if not a particularly fruitful one where the rpms are concerned. Thanks for the tip.
 
No :mrgreen:
 
I have two Yanmars ...... a 2GM20 in a 1901 Truscott launch and a 3YM30 in the R21EC and run both at lower RPM for considerable periods of time. The 2GM20 in the launch turns at 1200 rpm for 6kts and the 3YM30 in the Ranger turns at 2800rpm for 8 mph, 2100rps for 6mph ....... after I return to the dock I run both of them up to 80%/90% for at least four minutes to blow out carbon in the engine and the exhaust elbow. After the run-up I let them slow idle to cool (stabilize) the valves, guides, and upper cylinders for another three or four minutes ....... (don't shut down prematurely or valve/piston ring issues could develop) exhaust elbows are clean and the injectors have been performing without any fouling ..... so to answer your question ..... slow running is not a problem an long as you take the time to "exercise" your diesel after leisurely cruising. Fran Uteg
 
Our Volvo KAD44P has 5,553 hours on it so far. In the last 3,500 or so, we've run it at 6 knots (1,300-1,400 RPM) more than 95% of the time. Volvo tech wizards told me that once the engine is broken in, if it's run hard enough to keep the temps up to near normal (we run about 175 degrees at 6 knots), there's no problem. It's an electronic engine, which apparently helps.

The one thing they suggested to avoid was running at idle for long periods, especially before it was well broken in. The engine stays too cool, and unevenly so. If we do this (fishing) we have it well warmed up first. After extensive idling, it's good to run at planing cruise rpm (3,000-3,400 in our case) for long enough to get everything good and hot and clean it out.

They also suggested cruising at no greater than 10% off max RPM - which was not mentioned in our 16-year-old manual.
 
My engine gets warm up time on the way out of the no wake zone, and again on the way back in to the dock...about 10 minutes each way. Otherwise I'm doing 8 knots or 15 knots, about half and half, with a 5 minute full throttle run each outing. So far my engine seems happy.

Phil
 
I am not an expert on diesel engines. But when you think about it, if the engine could only run at 80% or MAX minus 10%, then we would have a whole bunch of diesel cars and trucks running amok all over the place. I think we need to put some common sense into the operation of our boats.

I looked at the Operator's Manual for the Volvo D3-200 and this is what I found.
Idle RPM = 700 RPM
Max Cruise RPM = 4000 minus 10 % = 3600 RPM
Max RPM around a beach = 1500 RPM
Engine shutdown - Allow the engine to run at low idle, in neutral, for a few minutes after operations are completed. In this way after-boiling is avoided at the same time as temperature equalization takes place. This is especially important when the engine has been run at high RPM under heavy load. (pg 45)

That said, you should be able to run your boat anywhere between 700 and 3600 RPM, depending upon conditions, desired fuel burn, etc. In addition to the note on engine shutdown, I recommend briefly revving the throttle (out of gear) to max a few times for a few seconds each time to help blow out the carbon. I also recommend running the throttle (in gear) to max (4000 RPM) for a few minutes every hour to help blow out the carbon.

I am sure there will be a lot of people with various recommendations on how to operate your boat. As a minimum, you need to operate your boat and perform maintenance on your boat in accordance with the equipment manuals. It is important to read your manuals to avoid warranty problems and make your boat run and last longer.

Enjoy your new boat.
 
In this bunch we have about a zillion turbocharged Duramax and Powerstroke diesels for pulling our boats. (and Ford now has a 3.2 diesel for it's Ranger pickups - not to mention all the Jetta TDI diesels infesting the roads)
I am willing to bet that after going for groceries, idling outside of the convenience store then creeping through the traffic jams and idling through traffic lights to get home not one of you has given even one second of thought to running your truck engine at 80% of rated RPM for 4 minutes in the driveway (or some such) to 'blow the carbon out'. Your truck engine will still run reliably for hundreds of thousands of miles - long after you have traded it off.
Yet, here we are agonizing for minutiae over the exact same design and type of engine in our boats.
Do you believe that Yanmar, et. al, making a few thousand boat engines a year know something about high speed turbocharged diesel engines that GM/Ford/VW/Case/John-Deere/etc. making hundreds of thousands of these engines a year do not know?
Do we notice a dichotomy here :roll:
I believe we are way over thinking this issue :mrgreen:
 
Hey Denny,
Thank god we don't have to use DEF in our marine engines or maybe we can start another thread on that! :lol:
 
Thanks for the input everyone. I appreciate the help. I think the general consensus is that: as long as I don't cruise in idle, and as long as I make sure to run the engine a planing cruise every once and while, I should be fine.
 
Oh yea Mike. And debating brand of oil should liven the joint up.
 
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