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Old 03-14-2013, 01:14 PM   #1
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Running engine w no load

I asked quite some time ago about what is so bad about idling an engine with no load. No response so I'm assuming on one knows.

I bought into it fully for most of my life but now I'm think'in it may just be some old wife's tale like thing that mechanics perpetuate because they heard it from someone else and it sounded good. Lots of that sort of thing out there and we lay-people never REALLY know if it's true.

Underloading issues? Too much information exists to reject it entirely but little evidence exists to say it can't be done safely either. LOTS of people doing it and hardly ever a problem.

In my years in Alaska I've run my engine at the dock every three weeks or so when we didn't go out. For a year or two I'd tighten up the spring lines and run it in gear to have a load on but for 3 or 4 years now i've just run out of gear for 10 min at 1100rpm and then at 1400rpm for 10 min and then a bit at 800rpm and then shut down. I have run up to and probably over 1/2 hour like this. John Deere dosn't approve I know nor do many or probably most boat owners. I suppose I'm a self appointed myth-buster but I don't have any hard evidence showing why it's bad to run an engine w no load. As a general practice I minimize idling for other reasons like noise pollution near other people ect.

But specifically I know of nothing that indicates that it's bad for engines to run w/o a load .... other than so in so says it's bad. And of course running w no load over long periods is even worse than running w only a light load. That is another issue.
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Old 03-14-2013, 03:12 PM   #2
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Eric--- What we were advised to do if we didn't use the boat for a month is to run the engines in the slip in gear so there is a load on them. The load is not to provide a load per se. It is the only way to get the engines up to temperature at a relatively low power setting (1,200-1,300 rpm).

This is for FL120s. Other engines may want a different treatment.

Originally we ran both engines in gear at the same time with one in reverse and one in forward to minimize the strain on the lines. But after talking to our diesel shop plus some other people in the marine diesel industry, we no longer run an engine in reverse under load because we learned the BW Velvet Drive is relatively weak in reverse.

So now we run one engine at a time in gear in forward. We run each one at 1200-1300 rpm for about half an hour. They get up to temperature (I'm talking coolant temperature here) in about 10 minutes at that rpm and then run for about 20 minutes at temperature.

Just starting them and letting them idle or fast idle with no load does not get our engines anywhere near operating temperature, and we were told this is not so good because it allows moisture to form in the engine, doesn't burn off contaminants, and other things I don't remember anymore. We were told that if we cannot run them at temperature it would be better not to run them at all.

Of course in this climate we are usually able to take the boat out at least once a month during the winter, the weather and my work and travel schedule permitting. And actually taking the boat out is the best medicine because not only do the engines get up to proper temperature and stay there for a long time, the movement of the boat through the water cleans off the bottom, rudders, and running gear.
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Old 03-14-2013, 03:23 PM   #3
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Diesels generate a lot of combustion byproducts and a lot of condensation inside the engine. The only way to blow the condensate and byproducts out of the engine is to get it up to operating temperature which will never happen without a load.

All of the various and different metals in the engine are designed to run at a specific operating temperature. At that temperature the metals expand to the design spec. If your rings, pistons, cylinders are run for too long substantially below that design temperature, wear will be premature.

You will not get any instant catastrophic problems from no load running but you are most definetly shortening the time between rebuilds.
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Old 03-14-2013, 04:02 PM   #4
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I asked quite some time ago about what is so bad about idling an engine with no load. No response so I'm assuming no one knows. ()

I bought into it fully for most of my life but now I'm think'in it may just be some old wife's tale .........Lots of that sort of thing out there and we lay-people never REALLY know if it's true. I agree!
..........................

LOTS of people doing it and hardly ever a problem. I agree!
............................

For a year or two I'd tighten up the spring lines and run it in gear to have a load on.............I still do, while getting a "load on" in my salon!

But specifically I know of nothing that indicates that it's bad for engines to run w/o a load .... Again, I agree and have researched this question extensively.
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Old 03-14-2013, 04:09 PM   #5
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Let's try not to let this turn into a flame war please, gentlemen. These are always the kind of threads that do.

Thanks!

Besides, I want to know too. I idle mine every now and then. Sometimes I put it in gear for a few minutes, sometimes not. I see the concept of build-up in the cylinders, but that seems like it gets blown out easily when I WoT out on the river after a long trip. The temp thing I get too, but these old cast iron motors like most of us have aren't exactly 250 HP outboards revving to tens-of-thousands of RPM's. (I'm just speculating)
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Old 03-14-2013, 04:16 PM   #6
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Let's try not to let this turn into a flame war please, gentlemen. These are always the kind of threads that do.
????????????? 5 posts and a warning?????????

This is a great subject and one that has been debated for years and I'll bet still has a lot of interest.
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Old 03-14-2013, 04:24 PM   #7
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The real question is what is the "worst" thing for you engine? I've heard that running your engine under no load is the "worst" thing you can do to it. I've also heard that letting a diesel sit unused is the "worst" thing you can do to it. So the original poster is asking a very reasonable question; if you can't take her out for a good run, and your options are limited to letting her sit or running a bit at the dock, what is best for your engines health and longevity? There seems to be general agreement that running under load is the very best, but if you can't do that? To paraphrase that famous boater William Shakespeare, "to run or not to run; that is the question!"
Personally, I run my boat at the dock when I can't take her out for some time. I do find that she will come up to regular operating temperature if left to idle for fifteen or twenty minutes.
By the way, the same question applies to your genny, but I create a load by turning on every light and accessory. I don't want to drift off topic here, but many diesel mechanics have told me the genny is typically even more neglected than your propulsion engine. I am not a diesel mechanic, nor do I play one on TV, but my recommendation is "Gentlemen, start your engines!"
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Old 03-14-2013, 04:53 PM   #8
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The issue as it was explained to me is that by running the engines only briefly, moisture and other contaminants will form in the engine and then just sit there doing whatever damage they may do until such time as the engines are run properly up to temperature. Hence the caution that it is better to not run the engines at all than to run them only briefly.
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Old 03-14-2013, 05:06 PM   #9
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I know it's nice to check things on the boat when you can't take it out for a while but why run the engine at all? Talk to construction companies and farmers particularly that have winter slow downs. During the winter, do they start there tractors, backhoes and dump trucks every 3 or 4 weeks? Not the ones I've talked to. I don't know the answer but I'm sure there are a few.
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Old 03-14-2013, 06:08 PM   #10
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In addition to condensate not getting blown off, which has already been discussed, extended idling can lead to oil dilution with diesel fuel. The process is that incomplete combustion in a cold chamber leaves unburnt fuel to work its way down the cylinders. In the big scheme of things most of our engines suffer a lot greater insults than a bit of diesel in the crankcase but in theory that could cause excess wear over time. I don't lose any sleep over it but I don't go out of my way looking for opporunities to idle the engines either.

I like to have the engines running before I start getting clear of the dock (untying spring lines & disconnecting the power hose) or getting ready to raise the anchor. That's because I'm a pessimistic SOB and its therefore always a pleasant surprise when the engines actually start but the result is that my engines likely idle for 15 minutes to half an hour every time we go somewhere. I don't worry about it - others might.
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Old 03-14-2013, 06:10 PM   #11
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There are really 2 different situations.

First there is starting the engine and letting it warm up before going cruising. IMO, if you going to start your engine let it idle, fast idle or whatever idle for 5 to 15 minutes, then take it out and cruise it for an extended period of time, idle time will have no appreciable effect. To me, warming the lube oil (not the coolant) to the point where it freely moves through the engine, turbo and oil filter makes all kinds of sense. Remember, your block heater doesn't materially effect the oil temperature as the heater isn't in the oil pan. Consider this, in 2003 I installed my current motor (Cummins 6CT 300) in my boat after freshening up the externals (water pumps, fuel pump, starter, alternator, etc). The motor had an estimate 5 to 10,000 hours on it from crabbing Chesapeake Bay. In 2005 I had it completely rebuilt. I run 80 to 90 days a Summer (late May to Early October). On every trip it runs at least 5 to 10 minutes at idle before leaving the dock. I'm guessing it has been cold idled about 600+ times in the 4,000 hours since rebuild. Engine runs like a clock burning up to 12 gallons an hour and uses less than 1/2 quart of oil between oil changes.

Regarding running it in your slip:
I would never idle my engine if I wasn't going to take the boat out and run it. IMO, you need to reach full coolant and exhaust operating temperature for at least 15 minutes for it to have any beneficial value.

Regarding how often should you run your boat in the off season:
My boat is out of the water from late October to early May. Sitting for 6 months every winter doesn't seem to have had any effect. I guess if you leave the boat in the water year round there is a case to be made for running the engine to dry out the engine room out and help prevent rust. If I'm not going to use the boat for an extended period of time, well there is peace of mind knowing she is high and dry.

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Old 03-14-2013, 06:17 PM   #12
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Depends on the engines to a fair degree. The Detroit service and operators manual specifically advises against it. "It" being idling with no load whatsoever. As for degree of "worst", overloading at high RPM is the worst. Look in your engine manual and see what the mfr wants you to do during the warranty period (beyond the "break in" period).
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Old 03-14-2013, 06:24 PM   #13
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[QUOTE=manyboats;141634]John Deere dosn't approve I know nor do many or probably most boat owners. But specifically I know of nothing that indicates that it's bad for engines to run w/o a load .... other than so in so says it's bad. QUOTE]

I think you answered your own question...

My feeling is that there is no NEED to do it, so why do it. In my case it is not the lack of load so much as the lack of heat developed w/o load. My Perkins engine will only heat to 160F w/o load. My Greymarine will get to 180F w/o load but that is still not enough to boil off water vapor which may have condensed in the oil.
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Old 03-14-2013, 06:32 PM   #14
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... My Greymarine will get to 180F w/o load but that is still not enough to boil off water vapor which may have condensed in the oil.
Believe the engine temperature gauge is measuring coolant temperature, not oil temperature. Also, higher temperatures less than boiling increase evaporation of water and the lighter distillates, no?
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Old 03-14-2013, 06:46 PM   #15
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Believe the engine temperature gauge is measuring coolant temperature, not oil temperature. Also, higher temperatures less than boiling increase evaporation of water and the lighter distillates, no?
True your gauge is measuring water temperature for sure. But oil temp does not get above 212F without some serious load and repeated heating / cooling (below 212F) is what causes water in the oil or your fuel tank too for that matter.

It has been known for years that auto engines used primarily for around-town driving, sludge up & die sooner than those used for interstate travel.
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Old 03-14-2013, 06:46 PM   #16
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Good posts all.
I like Boatpoker's input best. Byproducts? Condensation? I don't think a load in gear strech'in your spring lines will even be enough load on my little boat much less the majority of boats here. My Mitsu reaches 190 degrees in about 3 minutes. But I'm sure the oil will require a 50% load over time to come up to temp. Condensation in the crankcase may not get swept out and if it did it would be replaced w damp air in the boat. Then to open that can further where would the condensation come to rest when the engine is shut down. Any place I can think of would have a film of oil on the surface. Perhaps not thick enough.

The combustion by-products I would think would get swept out of the cylinder easily but while they were there They could adhere to valves, valve guides, pistons, rings and other surfaces.

So it looks to me that Marin's right that the engine shouldn't be started at all. At one time I was cranking the engine w/o the glow plugs on to pump oil to the bearings. That really seems like a harmless activity and at least it would rotate the sea water impeller to help avoid the vanes from taking a set.

So I've concluded at this point that cranking the engine now and then is probably a good thing and running at 50% load for 5 to 10 is required for proper lube oil function. But probably over half the boat owners on this forum don't ever get to 50% load.

So this idling issue is much like under loading while cruising and is also like basic under loading in that the harm done is so slight it's not measurable and the results aren't noticeable for long periods of time if at all. However some extreme cases have resulted in glazed cylinder walls.

Well I'll quit idling as discussed and I have never underloaded cruising at all. Haven't run the engine for a month or so and I'll be going to the boat the next few days but I'll just crank it a bit.

But I still think ther'e is more to know about the dangers of running diesels cold. And even though my coolant temp comes up to 185 degrees in 3 min the engine is still cold and will remain so until there's been a 50%load for a time on the engine.

What do you think Boatpoker?
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Old 03-14-2013, 07:05 PM   #17
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I take the boat out for a 2-to-4-hour trip even if not having a destination rather than run engines at the dock. It's not a problem, it properly exercises the engine and the boat's other systems, and even if I've traveled the route many dozens of times, each trip is unique.
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Old 03-14-2013, 07:16 PM   #18
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I know it's nice to check things on the boat when you can't take it out for a while but why run the engine at all?
Here's why we do it. We use our boat year round. So we don't change the oil in the engines until the end of our oil change interval. Which means that as time goes by the oil in the diesels gets dirtier and dirtier and more contaminated.

Most of us have heard the advice that if a diesel boat is going to be laid up for the winter, change the oil prior to the layup so that the engines are sitting with clean oil in them.

The reason I have heard for doing this is that as diesels are run contaminants build up in the oil that can "attack" bearing surfaces and such if the engines just sit for a long period of time. So changing the oil before a winter layup means the engines are sitting with clean oil in them which reduces or eliminates the potential for metal surface deterioration.

So...... we use our boat year round but there can be times when the winter weather and/or my work and travel schedules can conspire to prevent us from going out for a couple of months or in a few cases even longer. We still go up to the boat almost every weekend that I'm here, but we may not have the time or the weather to actually go out.

Since we have no way of knowing when these periods of not running the boat might occur, it would be impractical and unnecessarily expensive and time consuming to change the oil based on when we thought the boat might be sitting for a relatively long period of time.

So we simply run the engines at temperature for a half hour or so if we are unable to actually go out for four weeks. We chose four weeks simply because it's easy to remember, not because there is anything special about that interval as far as the engines are concerned.

From everything I have been told by folks we know in the marine diesel business and have read on the subject, running the engines (at the proper temperature) prevents the contaminants in the dirty oil from attacking the metal surfaces in the engine. Don't ask me why, though.

Now I don't think that any "damage" that might be done to the metal surfaces by the dirty oil sitting in the engines is going to be much to worry about over the course of a month or three. Or maybe it is, I don't know. Probably depends on how contaminated the oil has become.

But in addition to the oil thing, running the boat in gear at least once a month lubes the transmissions and "excercises" things like the water pump impellers, belts, and the other systems on the boat. So we view it as being a helpful thing to do, and if it isn't helpful it certainly doesn't hurt anything as long as the engines are brought up to temperature and run at temperature for awhile.

So that's why we run our engines periodically in the slip under load. Whether it's really accomplishing anything I cannot say because it's not my area of expertise. But it is the area of expertise on the part of the people who have recommended we do it, so we do.
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Old 03-14-2013, 09:47 PM   #19
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I know it's nice to check things on the boat when you can't take it out for a while but why run the engine at all? Talk to construction companies and farmers particularly that have winter slow downs. During the winter, do they start there tractors, backhoes and dump trucks every 3 or 4 weeks? Not the ones I've talked to. I don't know the answer but I'm sure there are a few.
I asked a well respected local diesel mechanic about running the engines during long periods of non use. I couldn't see a good reason to do so. He replied that at rest, some of the exhaust valves are open and these cylinders are open to the atmosphere through the exhaust system. This can lead to corrosion in the cylinders.

I'm not totally convinced but I do start and run my boat's engine once a month or so for ten or fifteen minutes. I make sure the boat is securely tied to the dock and put it in gear at a little more than idle speed so there's a load on it and so it will begin to heat up. I can only get it to 150 degrees or so this way, not the 180 degrees that's the optimal temperature.
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Old 03-14-2013, 10:08 PM   #20
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Good posts all.
I like Boatpoker's input best. Byproducts? Condensation? I don't think a load in gear strech'in your spring lines will even be enough load on my little boat much less the majority of boats here. My Mitsu reaches 190 degrees in about 3 minutes. But I'm sure the oil will require a 50% load over time to come up to temp. Condensation in the crankcase may not get swept out and if it did it would be replaced w damp air in the boat. Then to open that can further where would the condensation come to rest when the engine is shut down. Any place I can think of would have a film of oil on the surface. Perhaps not thick enough.

The combustion by-products I would think would get swept out of the cylinder easily but while they were there They could adhere to valves, valve guides, pistons, rings and other surfaces.

So it looks to me that Marin's right that the engine shouldn't be started at all. At one time I was cranking the engine w/o the glow plugs on to pump oil to the bearings. That really seems like a harmless activity and at least it would rotate the sea water impeller to help avoid the vanes from taking a set.

So I've concluded at this point that cranking the engine now and then is probably a good thing and running at 50% load for 5 to 10 is required for proper lube oil function. But probably over half the boat owners on this forum don't ever get to 50% load.

So this idling issue is much like under loading while cruising and is also like basic under loading in that the harm done is so slight it's not measurable and the results aren't noticeable for long periods of time if at all. However some extreme cases have resulted in glazed cylinder walls.

Well I'll quit idling as discussed and I have never underloaded cruising at all. Haven't run the engine for a month or so and I'll be going to the boat the next few days but I'll just crank it a bit.

But I still think ther'e is more to know about the dangers of running diesels cold. And even though my coolant temp comes up to 185 degrees in 3 min the engine is still cold and will remain so until there's been a 50%load for a time on the engine.

What do you think Boatpoker?
I agree. I never start my boat unless I am leaving the dock. My boat runs at 1.8gph at 8nmpg. or I can burn 8gph at 20 nmpg.

I like slow and cheap so I am running mostly underloaded but I run her up to full RPM for the last 15 minutes of the day to burn the crap out. Yes, I know I'm not running her right either but we do what we can to balance wear and cost.

I've measured many engines on sea trials with my thermal camera and infrared thermometer and I have never seen one get close to manufacturer recommended operating temperature unless run at least 65-70% of max RRPM.

As I said you are not going to cause catastrophic failure but you will shorten her life by prolonged idling.
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