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Old 17-04-2020, 12:07   #31
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Re: How many hours is too many?

I guess since the motor is in a Motor Sailer, built in 1974, been around the world twice and currently only sailed 5-6000 miles a year having a total of about 35,000 hours on the engine is pretty low.
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Old 17-04-2020, 12:23   #32
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Re: How many hours is too many?

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Continuous run, or nearly so engines do run for very many hours. Yes, you will get more total hours out of an engine that is never stopped. But recreational boats are not that. If fact the worst thing I've seen in marine engines is old, but very low hours.
Even thatís a maybe, my boat when I bought her had 500 hours on the motor, in 27 years. Iíve had her for 5 years and put another 1200 hours on it, and except for a pump impeller have only had to do scheduled maintenance.
Now I did finally change the original 32 yr old hoses last year.
Doesnít burn a measurable amount of oil between changes, and doesnít leak a drop either.
Now of course since Iíve bragged on it, it will swallow a valve or throw a rod or something.

I donít believe there is a metric you can go by to determine the engines state of health, itís really condition.
There have even been studies conducted by the FAA to determine if engines changed based on TBO are safer than ones changed based on condition, to find out that the TBOíd engines were not safer.
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Old 17-04-2020, 12:29   #33
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Re: How many hours is too many?

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Even that’s a maybe, my boat when I bought her had 500 hours on the motor, in 27 years. I’ve had her for 5 years and put another 1200 hours on it, and except for a pump impeller have only had to do scheduled maintenance.
Now I did finally change the original 32 yr old hoses last year.
Doesn’t burn a measurable amount of oil between changes, and doesn’t leak a drop either.
Now of course since I’ve bragged on it, it will swallow a valve or throw a rod or something.

I don’t believe there is a metric you can go by to determine the engines state of health, it’s really condition.
There have even been studies conducted by the FAA to determine if engines changed based on TBO are safer than ones changed based on condition, to find out that the TBO’d engines were not safer.
Yeah, we do get lucky sometimes. The boat in my avatar (a 1985) I bought in '92 had only 400 hours on it and it was good. Perkins 4-108 and never dripped a drop of oil! Go figure. On the bad low hour one's I've had , it was often the peripheral stuff often that was bad. Shafts, injectors, pumps etc.
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Old 17-04-2020, 13:30   #34
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Re: How many hours is too many?

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Average auto requires 10 to 20 HP to maintain 65 MPH, and average auto is 200 hp. So average auto at cruise is using about 10% to 15% of its power output.
https://auto.howstuffworks.com/one-horse-engine.htm
Most all newer cars will run quite low RPM at highway speeds, they may have a redline of 6500 or so, but usually even at 70 MPH don’t turn much more than maybe 2500

Average car is WAY overpowered, cause we like acceleration. Efficiency wise a much smaller engine would be way more efficient, but it could be argued that using only about 10% or a little more of available power is why they can last so long.

Most people run their boat motors harder than they realize, average 3600 RPM max motor run at 2500 RPM is often at least 50% power, and I think you will find many people run them that hard, or harder.

On edit, there is a very valid argument that maintenance should be scheduled based on fuel consumed, especially oil changes, but I assume it’s a lot harder to track, so it’s usually not done, but how much fuel you have used is a very good indicator of how hard it’s been run.
Yeah. How much fuel you use is probably a good indicator.

But your whole discussion above is about gasoline motors. I’m doing a more direct comparison to my Cummins diesel engine. Straight six diesel. That’s where my RPM and speed figures came from. And I imagine hauling the load of the RV with it as well.

It actually runs just like a boat engine.

Going down the highway, maintaining speed, with a load, it feels identical to a boat. Just sitting there at 2200 RPMs the whole way at 80 miles an hour.

At that speed with that load, I am using 8 gallons of fuel per hour. It gets 10 miles per gallon with that load.
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Old 17-04-2020, 14:02   #35
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Re: How many hours is too many?

I think Iím at about 626,000 hours. I donít know how much fuel Iíve consumed. Probably time for an overhaul. Oh, ...you meant my Diesel engine not me.
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Old 17-04-2020, 14:12   #36
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Re: How many hours is too many?

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I think Iím at about 626,000 hours. I donít know how much fuel Iíve consumed. Probably time for an overhaul. Oh, ...you meant my Diesel engine not me.
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Old 17-04-2020, 14:33   #37
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Re: How many hours is too many?

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Yeah. How much fuel you use is probably a good indicator.

But your whole discussion above is about gasoline motors. I’m doing a more direct comparison to my Cummins diesel engine. Straight six diesel. That’s where my RPM and speed figures came from. And I imagine hauling the load of the RV with it as well.

It actually runs just like a boat engine.

Going down the highway, maintaining speed, with a load, it feels identical to a boat. Just sitting there at 2200 RPMs the whole way at 80 miles an hour.

At that speed with that load, I am using 8 gallons of fuel per hour. It gets 10 miles per gallon with that load.
My last truck was a Duramax 4dr dually and I either pulled a 36’ 5th wheel or a JD410 backhoe, the backhoe was of course much, much harder.
But in truth I mostly ran empty like most light trucks, most of the time it was just me a tool box and a 100 gl fuel tank.

However there is absolutely no comparison at all with my baby Yanmar and a Duramax 32 valve four overhead cam, roller rocker common rail injection, with a water cooled turbo and an after cooler that was larger than the radiator. The Duramax was actually a joint venture between Isuzu and GM, and I had one of the early motors and it had an Isuzu dataplate.

Now I had a John Deere lawnmower with a 3cyl Yanmar that was actually a very close comparison to our average baby Diesel’s in our sailboats.

Our baby Diesels have more in common with small car spark ignition motors than “real” heavy duty Diesels.
But the part of the point I was trying to make is that almost no one will argue that gas motors will outlast Diesels and auto gas motors 10,000 is really no big deal. So I believe if run correctly then our sailboat motors ought to last as long as an economy cars does.
One very big difference is many autos are run nearly every single day of the year, while sailboat motors may sit sometimes for months between uses, and having water especially salt water in the exhaust system while they do all that sitting has to have an effect.

I believe you can run out a small Yanmar in less than 3,000 hours, have it slap worn out, or treated with extraordinary care it may can go 10,000.

It’s all about how well it’s treated, not so much how old or how many hours are on it.

Why I point out aircraft motors lasting only 1500 to 2500 hours is because they are run hard, pretty much wide open but at altitude if non turbo the power is down of course. But they don’t run high RPM, highest iHave seen is 2750 and that for takeoff only limited to 5 min, but most are cruised between 2200 and 2500 RPM.
They aren’t junk motors or poorly designed, they don’t last simply because they are run very hard, often cruised as high as 75% power.
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Old 17-04-2020, 14:49   #38
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Re: How many hours is too many?

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My last truck was a Duramax 4dr dually and I either pulled a 36’ 5th wheel or a JD410 backhoe, the backhoe was of course much, much harder.
But in truth I mostly ran empty like most light trucks, most of the time it was just me a tool box and a 100 gl fuel tank.

However there is absolutely no comparison at all with my baby Yanmar and a Duramax 32 valve four overhead cam, roller rocker common rail injection, with a water cooled turbo and an after cooler that was larger than the radiator. The Duramax was actually a joint venture between Isuzu and GM, and I had one of the early motors and it had an Isuzu dataplate.

Now I had a John Deere lawnmower with a 3cyl Yanmar that was actually a very close comparison to our average baby Diesel’s in our sailboats.

Our baby Diesels have more in common with small car spark ignition motors than “real” heavy duty Diesels.
But the part of the point I was trying to make is that almost no one will argue that gas motors will outlast Diesels and auto gas motors 10,000 is really no big deal. So I believe if run correctly then our sailboat motors ought to last as long as an economy cars does.
One very big difference is many autos are run nearly every single day of the year, while sailboat motors may sit sometimes for months between uses, and having water especially salt water in the exhaust system while they do all that sitting has to have an effect.

I believe you can run out a small Yanmar in less than 3,000 hours, have it slap worn out, or treated with extraordinary care it may can go 10,000.

It’s all about how well it’s treated, not so much how old or how many hours are on it.

Why I point out aircraft motors lasting only 1500 to 2500 hours is because they are run hard, pretty much wide open but at altitude if non turbo the power is down of course. But they don’t run high RPM, highest iHave seen is 2750 and that for takeoff only limited to 5 min, but most are cruised between 2200 and 2500 RPM.
They aren’t junk motors or poorly designed, they don’t last simply because they are run very hard, often cruised as high as 75% power.

I agree. And that’s the killer. Sitting unused. Mostly all of the ancillary parts around the core start going bad. But I’m sure there are some internal things going wrong also while things sit and rot.

But as is the case whenever we all talk boats, you and I are talking about two different things. Happens all the time on this forum. I’m thinking of one type of engine, you’re thinking of a whole different thing. When you are talking about our small engines, we don’t have the same engine.

I have a Perkins 6.354. Nearly identical to the Cummins turbo diesel in my truck.

354 cubic inches (5.8 litres) 120 BHP at 2800 RPM. Very close match, minus the turbo part. The Perkins is of course naturally aspirated being in an older boat that I have.
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Old 17-04-2020, 16:40   #39
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Re: How many hours is too many?

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Disagree strongly with this sweeping generalization. Components on the engine have service intervals that may include rebuild or replacement, but a well maintained and serviced naturally aspirated diesel engine will easily go 10,000 before it wears out. On the other hand, hi-output turbo/super charged Diesels common on sport fishing boats may be toast at 3500 hours (though in all fairness, have traveled at 25+ kts vs 7). That said, I had a Universal in a Newport 28 many years ago that didn't strike me as a particularly robust engine, but I was not as knowledgeable in Diesels so it could have been me.

To the OP : as others have said, compression check is a good indicator of wear of piston rings and/or valves. Wear accelerates when there isn't enough oil or the valves are allowed to get out-of-adjustment.

Unfortunately, checking compression on a diesel is much more difficult than a gas engine - you have to remove each injector, and it requires some sort of adapter which varies by injector. Net is that it can be expensive to have compression checked unless your mechanic happens to have the right adapter.

First engine check is cold start. Make sure engine is stone cold. Feel the oil pan and the coolant tank. Engine should start within a couple revolutions - not unusual for an engine to start within a half revolution. If it takes more than about 3-seconds of cranking, there may be a compression issue.

Second check would be exhaust. There may be some mild oil in the exhaust with a minor slick. Small amount of blue/grey smoke is not uncommon, but should disappear within a few minutes. Once warmed up, engine should idle smoothly without "loping" (RPMs varying up/down). Sustained or excessive smoking/oil slick or uneven running may be a sign of worn injectors or injector pump. Steam is normal depending on ambient temperature

Third check is blow by. If the cylinders are not holding compression, the pressure is getting past the rings or the valves which then pressurizes the crank case. A visual dockside check is to bring up the RPMs to about 1000 (neutral) and remove the oil fill cap on top of the valve cover. If there's a lot of escaping air - enough to float a tissue or paper towel, especially if it's laced with oil, there may be a compression issue.

Fourth check is underway sea trial. Engine should be capable of running WOT for 10-mins without blowing too much black smoke or overheating. Personally, this is where I want the owner's representative to drive the boat - if it does overheat, not my problem.

Finally, oil analysis. This will generate some strong push-back from other CF members. . It's a holy war - many feel its a waste of time and money especially with a single data point vs sustained trending. Personally, there is enough data in a single oil sample to make it worth the $40 to pull a sample. At the very least, it will tell you if there is sodium - salt water in the engine. There is a chance that the owner has recently replaced the oil, perhaps to hide a known defect. Check the oil filter - many mechanics use a Sharpie to say when the oil was last changed. Also pull samples of transmission fluid (less likely to have been changed) and perhaps coolant. Pulling the sample and interpreting it is not as straightforward as you'd think, but it's a good start.

OP mentioned checking for leaks. Leaks first show up as slight weep or white fuzz. These should all be remedied asap. There is no such thing as an acceptable leak on a boat. Bilge should be dry.

Good luck.
Peter
So:
1) First engine check is cold start.
2) Second check would be exhaust
3) Third check is blow by.
4) Fourth check is underway sea trial.
5) Finally, oil analysis.

The above is pretty reasonable to do. A compression test, which messes with someone else's engine, seems like a big ask. Can these test be run (other than sea trial) on the hard?
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Old 17-04-2020, 16:43   #40
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Re: How many hours is too many?

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Marine engines and generators have design ilfe of 5,000 hours.

That is nonsense, in theory and practice!
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Old 17-04-2020, 16:57   #41
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Re: How many hours is too many?

Side question. When a marine diesel has been sitting for six months or a year, it almost always smokes like crazy for the first few seconds of operation. At least a lot of them do. Especially the older ones. What causes that?
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Old 17-04-2020, 17:16   #42
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Re: How many hours is too many?

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That is nonsense, in theory and practice!

Well then what do you think the design life limit is, or do you think the engine manufacturers throw something together and hope it lasts a reasonable time?
They do design to meet specifications, and life is one of the parameters, size, weight and power are some others.
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Old 17-04-2020, 17:22   #43
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Re: How many hours is too many?

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Side question. When a marine diesel has been sitting for six months or a year, it almost always smokes like crazy for the first few seconds of operation. At least a lot of them do. Especially the older ones. What causes that?
Could be several things, but the bores being rusted is one possibility.
Aircraft also often sit, and when they sit the cylinder bores develop a slight rust covering, its cleans off very soon after starting of course, but it causes wear, enough cycles of cleaning off the rust and you end up with polished bores.
Some people will put the crankcase breather tube in a baby bottle of desiccant so that any air drawn into the engine will hopefully be dried and not cause the rust.
Now a marine engine’s exhaust has salt water in it, pretty bad thing by comparison.

But it could also be excess fuel if the engine doesn’t start right away, fuel is of course often grayish and smells like fuel while oil is blue and stinks like oil, so what color are you seeing? Do you see a sheen on the water, if not it may be just soot, especially if it doesn’t hang in the air and is black
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Old 17-04-2020, 17:26   #44
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Re: How many hours is too many?

How many years of human life is too many? Sure there were a few who lasted 115-120 years, 122 I beleve is the documented world record. But a good number living reasonably healthy lives without catastrophic events, getting timely medical help, no booze or smokes in excess and with a bit of luck thrown in will expect to last between 80 and 90 years. So even uynder the almost ideal conditions that's well short of the apparent capability of around 120. And not living healthy lives in a unhealthy environment life expectancy is much shorter than that.
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Old 17-04-2020, 17:27   #45
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Re: How many hours is too many?

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So:
1) First engine check is cold start.
2) Second check would be exhaust
3) Third check is blow by.
4) Fourth check is underway sea trial.
5) Finally, oil analysis.

The above is pretty reasonable to do. A compression test, which messes with someone else's engine, seems like a big ask. Can these test be run (other than sea trial) on the hard?
Not really. Boat needs to be in the water to cool exhaust. I suppose done sort of hose could be hooked up, but I don't thing that's practical. Engine needs to be brought up to temp. If you decide to pull an oil sample, should be pulled on a warm engine and not from the bottom of the pan.

Why is the boat on the hard? How would you sea trial and sail? If this is a rock bottom bargain, you take chances. Might work out fine. But might not too.

Good luck

Peter
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