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Old 06-07-2010, 13:43   #1
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Engine Hours

Two questions:

Can someone explain why are engine's rated in hours? 100 hours at 3500 rpm is not the same as 100 hours at 1000.

I know car diesels. I know that with proper care they will easily last several hundreds of thousands of miles. Even with minimal care, they will last 100,000 miles. If you were to travel 60 miles hour, 100,000 miles is 1666 hours. So how many hours can I expect out of a marine diesel, with average care?

Is there an amount of hours that I should be concerned over? I have no problems buying a car diesel with 100,000 miles on it.

Open question, are some models better than others?

Ok that was three questions.
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Old 06-07-2010, 14:42   #2
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"Use spectrum" between individuals can be different - but how to quantify this between different boats with different users almost impossible without data loggers. Even many expensive aircraft just use total hours + number of start cycles.
My engine has 5000 hrs - a friends has 9000. With good oil and regular maintenance they will go a long time.
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Old 06-07-2010, 15:58   #3
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An hour meter measures itself. Not the load on the engine, not the wear on the engine, just itself.

A data logger, such as FraidNot mentions, could keep track of fuel burned, time spent at various RPM and load settings, etcetera and thus give a more accurate picture of the actual state of the engine.... but it's much simpler to just say "change the oil every XXX hours" and to check the belts and vital fluids on a regular basis.
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Old 06-07-2010, 16:09   #4
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On diesel engines I am familiar with the hourmeter is driven based on rpms not a timer.
The manufacurers use a certain number such as 2000 rpm, or other, to equate to one hour. run faster hours more will accumulate, or less hours if run at less rpm.
15-20k hours seem like a common life span for a well maintained diesel.
Steve
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Old 06-07-2010, 17:56   #5
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Quote:
Originally Posted by mpc7002 View Post
Two questions:

Can someone explain why are engine's rated in hours? 100 hours at 3500 rpm is not the same as 100 hours at 1000.
This is a very good question and one I haven't even thought of myself, despite my considerable experience with diesel engines.

What I do know is this:
For road going diesel engines (trucks and buses) in Australia some of the larger fleet operators in our country have found that a km (or miles) based assesment is also not accurate enough, for the same reasons you said. 100 km of suburban usage with a light load is not comparable to 100 km of highway usage, heavily loaded, however the miles recorded on the spedo are the same. These fleets are basing their oil change intervals on a fuel used criteria. They claim that the manufactureres are too conservative and therefore their mainatence costs are higher than they need to be. If the engine is lighly loaded, then it uses less fuel and heavily loaded uses more. So distance travelled divided by fuel used would give an indication of how hard the engine has worked and therefore what life may be left in it. If you determined how much fuel would be used at an average load situation for the number of hours the manufacturer recommended, you could probably arrive at a better method for calculating service intervals by changing oil after that certain number of liters (or gallons) was used. If a previous owner had logged fuel usage and the hours used you may be able to estimate how hard the motor has actually worked for the hours logged. This works better for on road engines than marine engines becuasue what you don't want is an old marine engine that's spent 90% of it's time idling. An oil sample might tell you if fuel is getting past the rings.

But who's going to do all this on a boat?
Me......I change the oil every Christmas.

Greg
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Old 06-07-2010, 18:31   #6
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Hours of operation in a marine application can't be directly correlated with automotive uses. Simply put, automotive uses will have the engine running at 20% of it's total output potential 90% of the time, possibly less. While most marine applications with a similar size engine will run at 90%(+) potential output 90% of the time. This is a huge difference, so direct comparisons are useless.

On the other hand aircraft engines and stationary engines do relate well to marine applications.

Hours are used simply because it's an easy comparison, particular between similar applications. Also as pointed out it makes routine maintenance a fairly orderly thing across many possible applications.

It's certainly very possibly to base filter change outs on particulate sensor data. Of course this is an added but accurate expense. If you really wanted to get anal about it, maybe a bearing material sensor just up stream of the oil filter (yep, I've seen them), to tell you when the engine has had enough. The hour meter is looking like the cost effective choice.
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Old 08-07-2010, 20:40   #7
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Ok, thanks for the input.

Is there a maintenance schedule for a marine engine, like there is for my car?

My car has recommended maintenance at 15K, 30K, 45K, 60K...
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Old 08-07-2010, 20:59   #8
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You should have an Operators Manual for your engine, it will give the service intervals for different check maintenance intervals, for example
Engine oil and filter change every 250 hrs (varies according to manufacturer)
Change air filter every 300 hrs, or yearly whichever comes first. also varies by manufacturer.
Very much like the manual for your car or other machinery.
Good luck,
Steve

first and so on for everything you to check or change.
if you do not have one maybe you can download one or else contact the engines local dealer or manufacturer
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Old 08-07-2010, 21:07   #9
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Once again thanks all for the advice.
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Old 08-07-2010, 21:41   #10
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Quote:
Originally Posted by PAR View Post
. Simply put, automotive uses will have the engine running at 20% of it's total output potential 90% of the time, possibly less. While most marine applications with a similar size engine will run at 90%(+) potential output 90% of the time. This is a huge difference, so direct comparisons are useless.

.
G'Day PAR,

I've seen statements like this for years, and have often wondered whether they really apply to engines in sailboats. Don't know about others, but I have never run my engine (in any of the three inboard yachts I've owned) at 90% of max output for more than very brief periods. More typically, the donk is used to idle in or out of anchorages/marinas/etc, or to cruise at something like 2/3 of hull speed, where the load might be on the order of 30-50% of max. There have been a few times where I've run it at higher loads for a couple of hours (like trying to beat cyclone Xavier into a safe anchorage in Vanuatu), but even then I don't think I reached 90+%.

Perhaps your data reflect powerboat usage, but I don't see many yachts running their engines that hard routinely.

But, I do agree that hour meters are only vague reflections of engine usage. I think they er on the safe side, though, and for most yotties time rather than hours of usage will drive maintenance oil changes etc. (As in Greg changing the oil every Xmas!).

Cheers,

Jim and Ann s/v Insatiable II lying Manly, Qld, Oz
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Old 09-07-2010, 04:38   #11
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Marine, aircraft and stationary engines run heavily loaded, nearly all the time. Automotive applications only experience something close to this type of loading, when attempting to leave a stop light at full throttle, on a 30 degree grade, with the trunk full to max, the passenger load to max and dragging a trailer too. Even if the car doesn't use WOT, once rolling it will reduce it's throttle setting dramatically there after, which isn't the case with marine, aircraft or stationary applications.

Hour meters are an accurate method of engine use, if the same skipper uses the boat. It will reflect their preferences for wear and tear. The recommendations for routine maintenance naturally are conservative, knowing full well some will double the change out limits and others will religiously pull a part at it's designated hour.

Me, I'm a two times over engineer and can pretty much guess at the "margins" the manufacture is working into their product. In this regard I'll run well past advertised recommendations on most everything. A TV commercial currently running here in the states, for a major motor oil brand, brags that it tests it's oil at the recommended oil change interval (automotive) and it still passes the lubrication, friction reduction, particulate suspension (etc.) tests at this time. Basically they're telling everyone that their oil change interval recommendation, is little more then a ploy for you to buy more of their product, because by their own testing (and admission) you clearly don't need to.
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