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Old 04-08-2013, 07:04 AM   #101
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And gas doesn't slobber with long term under loading , or cost a grant to put to sleep (BY DA BOOK) every winter.
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Old 10-09-2013, 10:00 AM   #102
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Originally Posted by CPseudonym View Post
I suppose what has me confused are those that feel idling, even for a half hour or so is detrimental to engine life. Burns fuel but there is more damage from over loading IMO.
I just spent quite a bit of time re-reading all the posts on this thread as the subject really hasn't been put to bed adequately. (IMO)

With winter coming on and my boat sitting more than usual, I continually wonder about my engine's health. I've been seriously contemplating a prop change with the expectation that I could milk another knot or two out of the boat.

I then turned to my Cummins Guru, Tony Athens, to see what his feelings are on the "over loading vs. under loading" debate.

Here is his treatise on that subject.
Engine Life vs. Engine Loading
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Old 10-09-2013, 11:01 AM   #103
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Walt, just realize he is talking about high strung diesels(like you and I have) and this is likely not as important to someone that is running a Lehman at relatively low loads. Yanmars are in this same class and I still don't see the failure rates on Yanmars like I do Cummins. You generally don't run your engine heavily loaded so it will likely never see an early demise like the ones Tony is talking about. But like he is talking about, it seems to happen in that 1000-1500 hour range. Maybe it just takes that long for a boat to gain enough weight paired up with the ignorance of owners before the engine gives up the ghost.

I run my boat at 2400RPM on plane. And I have it propped to run 200 over at WOT....probably even a bit more than that. So I feel I am not working them terribly hard. I was discussing with Timjet about the longevity of these engines. And you know my opinion of them. I really do think they are good engines. I think the issue is they are so good that they mask symptoms of problems until it might be too late. A good example of this is when I got water in my fuel from a failed fuel cooler. The racor can only catch so much water before it fills up and water starts getting to the engine. do you think the Cummins gave me any indication that it chugging water??? Nope. Not until I shut down and then started back up again did I notice the smoke and further diagnosed as two failed injectors. I think any other engine in this scenario would have just shut down. But the Cummins just keeps on chugging no matter what....even if it is chugging water. I was fortunate that it didn't do more damage.

Speaking of fuel coolers, Mr. Athens isn't a fan of them. As a Cummins certified dealer, I don't think he can come out and say that you should take them off. But read the link below and read between the lines. They take them off of brand new engines and bypass them. I would highly suggest you either replace yours or bypass them. Since you run your boat lightly loaded(ie low fuel flow) and where you boat is never really hot, then fuel coolers are likely not a big need. I have a hard time completely bypassing mine since it is so damn hot here but have been running one bypassed just as an experiment. I will be putting new fuel coolers on both next week. My compromise on the fuel cooler issue is to replace them every 2-4 years....just like servicing the aftercoolers. They are relatively cheap and extremely easy to change out....or at least in theory as the outboard side of my port engine is a PIA to get to. Anyway, another very inexpensive part on this engine that can do some very expensive damage.

Understanding Marine Fuel Coolers

And for anyone else reading this, the link above also has many great related articles if you click on "Tony's Tips". He is extremely knowledgeable in the operation and maintenance of Cummins engines and also general diesel engine theory.
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Old 10-09-2013, 11:54 AM   #104
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Yes Walt he does have "a few things to say".
I read it all and don't recall him mentioning engines making 20 to 30hp per liter like most of us have. I don't see that engine loading should change w lower output engines ... it just becomes less of an issue. I've always thought a bit under propped is best (I like 50 to 75rpm) and I always try to achieve that. In our type of boat if you're under propped you can't over load as long as you stay below the maximum continuous rpm specified by the engine manufacturer.
Thanks for posting this Walt as there are always those that think a quieter engine is less stressed whereas higher rpm less load = greater engine life.
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Old 10-10-2013, 06:16 AM   #105
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I read it all and don't recall him mentioning engines making 20 to 30hp per liter like most of us have

He really never gets into engines that are designed to produce 30 hp per liter and operated a 5!
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Old 10-10-2013, 09:10 AM   #106
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Ok let me throw this out there. What about Detroit 6-71's that sit at idle overnight each night for weeks on end in semi-tractors? I know they say underloading will wash the cylinders and lead to reduced life but what about al the truckers that have 500,000+ miles on there trucks, and I don't buy the marine VS road debate. An engine has no idea if it's in a boat or a truck.
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Old 10-10-2013, 10:25 AM   #107
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I too would like clarification on the no load/idle question as Knotheadcharters stated. I have always tried to adhere to the advice of running WOT for a short time as we head back home to help keep the cylinders clean of buildup but wondered how truck diesels survived with all the idling they do. Obviously I am very ignorant here but curious about the info and logic.

We own two boats one a Willard 30 with a Perkins 4-108 and the other a Grand Banks 36 with twin Lehman 120's.
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Old 10-10-2013, 10:28 AM   #108
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You're absolutely right knotheadcharters (wish you could shorten that one up) but you've left something out. The truck will soon be working very hard. The driver will be coaxing the truck up hills and accelerating it from a dead stop all day long. The trucks weigh 10 to 40 tons. The truck engine will do work that most all trawler engines will never see. And for more hours than they idle.

And most all trawler engines don't die but I hear a lot of talk about them smoking and hear many other complaints that may not come from a healthy engine. Most people in our culture aren't healthy either. Most all of us are underloaded.

Regarding my post I was not saying saying trawler engines will die from underloading (a few will) but saying they would be better off run properly like the manufacturers advise owners to do. They will have more power and compression. Start quicker and smoke less. My comments are just saying it's better to run trawler engines at 50 to 75% load. One other thing ... I have never heard of a manufacturer recommending a 25% load.

And the truckers idling their engines for hours aren't doing their engines any favors ... It's just convenient for the driver. I used to have breakfast in a restaurant w a man that had 10 or 15 trucks on over the road duty and he wouldn't allow his drivers to do that.

It's not death .... it's just not good.
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Old 10-10-2013, 10:48 AM   #109
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Originally Posted by knotheadcharters View Post
Ok let me throw this out there. What about Detroit 6-71's that sit at idle overnight each night for weeks on end in semi-tractors? .
They all wore out from excessive idling and were replaced by diesel heaters about 20 years ago.

On a more serious note though, isn't there a difference between the original posting saying no load - meaning idle - and low load meaning running your diesel at say 10 to 20% load? As previously mentioned, so long as temps for water and oil are within book recommended operating specs it would seem most agree "no problem."

Last year I walked from a very good deal on a vessel with twin Cat 12s that would operate at about 15% load or 1150 RPM to achieve hull speed of about 9 knots. Cat said no problems would arise when running these engines at hull speed but -------- To do book maintenance by the hour or date was no different than had the engines been operating a 80% power. The yearly book maintenance costs, assuming no breakdowns, per engine came out to about an average $3000 per year per engine.

My take was that to get a lovely big SD vessel designed to operate at 18 knots and then run it at hull speed was not good - for many reasons. Such as:
  • Rudders and stabilizers have less control at lower speeds
  • Fuel tanks/loads are undersized (for the type of trips we like to do) to keep weight down.
  • Very big transmissions and running gear, as with the engines, remain a high cost maintenance endeavor.
  • On engine alternators, cruise gens or hydraulic PTOs are running too slow to adequately power things or replenish batteries on a timely basis.
  • The engines are not operating within their better BSFC range.
My take is run your vessel however you feel comfortable, but don't think that lowered RPMs equate to longer maintenance intervals and a no worry attitude.
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Old 10-10-2013, 10:55 AM   #110
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Keith,
You don't need to go WOT back to port. It's good to do it for a minute at times to see if your engine is propped right and to test the engine for performance. Also to run at about 75% load for "a while" to insure your engine is ready to work if called to do so. But mostly to insure there's nothing wrong w it. 75% load for the Lehman Ford is about a 4 gph rate. Whatever rate (rpm) produces 4gph .. on your boat.

When I bought my Willard about 9 years ago I opened her up in the channel just so of LaConner. Ran fine for almost 2 minutes and then it died. Right there in the channel. It started a minute or two after but had I not done that I would not have known there was anything wrong w my engine. I repowered not long after that but not because of the engine dieing in the channel.

I run my Willard/Mitsu at 50% load most all the time. One gph. That's 700rpm down from 3000 (it's rated rpm) and work it harder at 500 rpm down at times.

Marin has coped well w this issue over time and now I believe he runs his engines at 3gph (50% load) most all the time. In the past he was overpropped but now has repitched props and he attains 2500 rpm at WOT. You may want to check w him as I do believe he has the same boat as you w twins. Same would hold true for a single though ... you'd just go slower.

AND .. this has been discussed extensively in the past.
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Old 10-10-2013, 11:15 AM   #111
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Eric, still an interesting discussion to me as some new points have been introduced. Yes, I have searched the archives and read many threads on this topic and finally decided to ask a question about the truck/marine idle issue knotheadcharters brought up. We do not run WOT very long, just bring it up on the way home for a few minutes and monitor all instruments as well as check engines with IR heat gun to assure me that things are going well. It is one of the ways I try to stay on top of our maintainance. 2 years ago we were trolling in our Willard at 850 rpm's and had alarms go off. We had been running for about 2 hours fishing at that speed before the alarms went off. I thought it might be a low rpm issue so shut everything down, checked all fluids, started it and checked temps of manifolds and exhaust water, everything was fine. Ran it at anything above 1000 rpm and no issue, go to anything below 900 and after a few minutes, alarms. Pulled into Friday Harbor and started checking sensors, pumps and impellers. Went to Jensen's Marina and took sensors with me to get checked out, they checked as dead so replaced them. Since then no issues. Spent 2 days fishing off San Juan Island at idle speeds and no problems since.

This is why I am curious about this topic, previous threads have not addressed it quite like the last few posts for me.
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Old 10-11-2013, 06:33 AM   #112
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Running at WOT for a while does zero to clean the cylinders.

What is required is to get behind the piston rings clear of gunk.

Pressure from combustion gets behind the rings and causes the seal.

Light load is low pressure so the rings do not seal, giving blowby and oil contamination. The light touch of the rings burnishes the honeing off the cylinder walls increasing wear and oil use.

15 Min is hardly enough time to evaporate the combustion by products out of normally cold oil.

An oil change more frequently is more useful.

Da Book usually has time in engine as well as operating hours for oil change requirements.
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Old 10-11-2013, 10:43 AM   #113
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They all wore out from excessive idling and were replaced by diesel heaters about 20 years ago.

On a more serious note though, isn't there a difference between the original posting saying no load - meaning idle - and low load meaning running your diesel at say 10 to 20% load? As previously mentioned, so long as temps for water and oil are within book recommended operating specs it would seem most agree "no problem."

Last year I walked from a very good deal on a vessel with twin Cat 12s that would operate at about 15% load or 1150 RPM to achieve hull speed of about 9 knots. Cat said no problems would arise when running these engines at hull speed but -------- To do book maintenance by the hour or date was no different than had the engines been operating a 80% power. The yearly book maintenance costs, assuming no breakdowns, per engine came out to about an average $3000 per year per engine.


My take was that to get a lovely big SD vessel designed to operate at 18 knots and then run it at hull speed was not good - for many reasons. Such as:
  • Rudders and stabilizers have less control at lower speeds
  • Fuel tanks/loads are undersized (for the type of trips we like to do) to keep weight down.
  • Very big transmissions and running gear, as with the engines, remain a high cost maintenance endeavor.
  • On engine alternators, cruise gens or hydraulic PTOs are running too slow to adequately power things or replenish batteries on a timely basis.
  • The engines are not operating within their better BSFC range.
My take is run your vessel however you feel comfortable, but don't think that lowered RPMs equate to longer maintenance intervals and a no worry attitude.

That was a good post, and a good explanation of the pros and cons of larger vs smaller engines.
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Old 10-11-2013, 12:37 PM   #114
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FF wrote;

"Running at WOT for a while does zero to clean the cylinders."

May reduce glaze if it's present and definitely will get the oil hot and probably help the ring situation but FF may be totally right too.

But running at WOT is not only not required but may do more damage than good. WOT for "a while" over a minute is not healthy for any engine if it's even slightly overpropped. If 100 rpm underpropped or propped at rated rpm it would be "ok" if it was in compliance w the manufacturers specs. Instead of "running at WOT one could/should run at a heavy load say 2 or 300 rpm down from the rated rpm. That should get the load and the temps up w/o the very real chance of overdoing it and causing damage or excessive wear.

Along these lines I've been thinking there is a possibility that the overheating issue w the back cylinder on the Lehman may be related to over propping. From what I've read the size of cooling passages and flow rates of coolant is not as easy to orchestrate from an engineering and design standpoint as one might think. Too much velocity of coolant and there's the threat of cavitation and too little may not cool enough or cause other problems like one little spot that tends to boil. And as to water jacket size it's not just bigger is better. You can't change the size of coolant passages but you could change the water pump pulley or make your own and change the coolant velocity.

Generally speaking over propping insures that you won't have the flow or volume of coolant and lube oil that the engine was designed for. Overpropped there will be more heat and less coolant from both oil and water jacket coolant. And of course underpropping would insure there would be an excess.

Re FF's post perhaps adding extra oil detergents would help more than running at WOT. Oil additives can be risky business though. But if one didn't have a glazing problem detergents just may help.
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Old 10-11-2013, 12:38 PM   #115
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I believe running at "one bell" caused me to have to replace the exhaust hose on my starboard engine. The theory being that at low speed the exhaust riser is only putting out cooling water from the bottom holes, allowing the top of the exhaust hose to overheat. Am I right?
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Old 10-11-2013, 06:32 PM   #116
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I have a 6 354.4 range 4 Perkins for last 15 years.I warm it 1/2 hour before using then 3 hour steam at 2200 rpm.Hauling crab gear with hydraulics engaged 8-10-12 hours at idle then back home 3 hours at 2200.I let it idle 1/2 hour before shutdown.I use Rottela 15-40 and change it every 150 hours.I believe oil is cheaper than machinery.My engine has never let me down and still operates same as new.Once a while I give her WOT 10- 15 minutes at most.At layup I cover exhaust airtight and never start engine in winter time.She still smokes a little at start up.Believe this is the nature off the beast from what I have read on internet.
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Old 10-11-2013, 06:39 PM   #117
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"At layup I cover exhaust airtight and never start engine in winter time"

I think that's about what I'm going to do next few days.

Why not cover the intake?
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Old 10-13-2013, 01:37 PM   #118
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Diesel engines are much more efficient than gasoline engines. A higher proportion of the fuel actually does work and less heat is generated in a diesel. We have found useful things to do with the wasted heat by-product such as heat our shower water, but largely we would prefer the fuel consumed to make less wasted heat and do what we really want, propel us.

The downside of this efficiency is that we need to run the engines under load to generate enough heat to warm the engine to its design temperature. Running without a load will never do this. An example of this is the VW diesel - in cars, it does not produce enough heat to warm the car's interior so the designers put "glow plugs"(they call them that!) in the water jacket so the water will heat up and it will also help heat the engine block and help bring the engine to its design temperature.

If you run diesels unloaded or at idle for a long time you are doing damage. If your boating style is such that you often run your engines at idle or under-loaded, you should be running gasoline engines which are much less efficient and produce a lot more wasted heat and can run for hours at idle with (on older designs) only fouled plugs.

Many gensets fail prematurely because they are started to run a toaster or a coffee pot, sadly an insufficient load for a genset.
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Old 10-13-2013, 01:45 PM   #119
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The downside of this efficiency is that we need to run the engines under load to generate enough heat to warm the engine to its design temperature.

Running without a load will never do this. An example of this is the VW diesel - in cars, it does not produce enough heat to warm the car's interior so the designers put "glow plugs"(they call them that!) in the water jacket so the water will heat up and it will also help heat the engine block and help bring the engine to its design temperature.



That's a good one ...
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Old 10-13-2013, 02:17 PM   #120
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Ever owned a Golf TDI Rick?

I just saw you are in Lauderdale where cars don't even have heaters. You're forgiven.
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