How many hours is too many?

[a64pilot]

Here is an FAA Advisory Circular that explains design life limit
https://www.faa.gov/documentLibrary/...70-1_Chg_1.pdf

[a64pilot]

Originally Posted by skipmac

That will depend very much on the engine. Many "manufacturers" of marine engines buy the blocks from outside sources, some of them industrial blocks rated for 10,000 hours or more.

But those are not manufacturers and you of course know that cause you put that in parenthesis.
However the mission profile is extremely important in design life, a propellor in an aerobatic airplane won’t last 1/4 the time it will in a transport category aircraft due to how it’s operated, so to say an industrial engine is designed for 10,000 hours means of course if it’s operated within its design parameters, something that it may not be in a marine application.
Very, very often the only difference between what amount to identical engines with widely different TBO’s is simply how much power they are allowed to produce, turning the Governor down has a tendency to greatly increase service life as opposed to an engine that it’s max HP limit is much higher.
For instance GE sells the identical engine as a 750, 800 and 850 HP, and that is industry practice, even the little Suzuki outboards on our dinghies the 9.9, 15 and 20 are identical engines, different computers and maybe a restriction plate or similar.
If they are all run at 75% power, which one do you think will last longer?

[skipmac]

Originally Posted by a64pilot

Very, very often the only difference between what amount to identical engines with widely different TBO’s is simply how much power they are allowed to produce, turning the Governor down has a tendency to greatly increase service life as opposed to an engine that it’s max HP limit is much higher.
For instance GE sells the identical engine as a 750, 800 and 850 HP, and that is industry practice, even the little Suzuki outboards on our dinghies the 9.9, 15 and 20 are identical engines, different computers and maybe a restriction plate or similar.

This is the case with the 30 year old Westerbeke (which is a Perkins which is I think a Mitsubishi). It is rated continuous HP from 38 @ 2000 rpm to 52.8 at 3000 rpm to max 69hp @ 3600 rpm. Seldom run mine over 2500rpm.

Originally Posted by a64pilot

If they are all run at 75% power, which one do you think will last longer?

How many guesses do I get?

[Chotu]

You know, I was wondering why people replace older diesel engines and I created a thread on it. Your question about the hours really had me wondering.

So I did a little bit of an exercise.

Earlier someone said marine diesel engines are built to go 5000 hours. Comparing that to diesel engines in pick up trucks, which are the same size, the average speed of a vehicle in a non-urban area is about 45 mph.

So that’s about 225,000 miles on the boat’s odometer at 5000 hours. If it were a vehicle. Now, some engines are tired at that point. Many engines go twice as far as that. Specifically thinking of some Volvos and Mercedes engines that go like crazy.
If the body of the car holds together, the engine goes 1,000,000 miles. Some Japanese engines too. Mitsubishi

Does anyone in the UK know how many kilometers those old taxi cabs used to get with the Perkins engines?

I think this is a good exercise to visualize what hours really mean. Because we are all familiar with vehicles.

[MAJICDAN]

You need to have a mechanic experienced with your motor check compression and give you an opinion.
My Perkins 6.354 normally aspirated motor went almost 30,000 hours before I did a major overhaul and then it could have gone a lot longer.
I have about 6500 hours on this rebuilt.
We cruise 5-6000 miles a year.
The previous owner went around the world.
Every model of motor is different.
How hard do you run it.
Oil changed
Type of oil
Maintenance schedule
Good luck

[Calif.Ted]

Late 90's the shoreboats in Avalon, Catalina Island used that Perkins so I asked the owner how long they lasted in taxi service. He replied that he didn't know because he just replaced them every 10,000 hours.

[a64pilot]

Originally Posted by Chotu

You know, I was wondering why people replace older diesel engines and I created a thread on it. Your question about the hours really had me wondering.

So I did a little bit of an exercise.

Earlier someone said marine diesel engines are built to go 5000 hours. Comparing that to diesel engines in pick up trucks, which are the same size, the average speed of a vehicle in a non-urban area is about 45 mph.

So that’s about 225,000 miles on the boat’s odometer at 5000 hours. If it were a vehicle. Now, some engines are tired at that point. Many engines go twice as far as that. Specifically thinking of some Volvos and Mercedes engines that go like crazy.
If the body of the car holds together, the engine goes 1,000,000 miles. Some Japanese engines too. Mitsubishi

Does anyone in the UK know how many kilometers those old taxi cabs used to get with the Perkins engines?

I think this is a good exercise to visualize what hours really mean. Because we are all familiar with vehicles.

The huge difference between aircraft and marine engines compared automobile engines is the power level they are run at, aircraft and marine engines are very often run at set power and run hard. Automotive engines are most often run at very low power settings, with seldom used high power and even then short duration.
But average cars average speed is likely 20’s mph or so. I know as our Prius for whatever reason displays average speed, we put 250,000 miles on it in about 7 years, so obviously most miles were highway, and it’s average speed is mid 20’s. The time you spend at stoplights, waiting in line at drive throughs etc really kills the average speed.

But assuming it’s average speed was 25 mph, at 250,000 miles, thats 10,000 hours and it doesn’t burn a drop of oil and as you say 250,000 miles is very common.

[Chotu]

Originally Posted by a64pilot

The huge difference between aircraft and marine engines compared automobile engines is the power level they are run at, aircraft and marine engines are very often run at set power and run hard. Automotive engines are most often run at very low power settings, with seldom used high power and even then short duration.
But average cars average speed is likely 20’s mph or so. I know as our Prius for whatever reason displays average speed, we put 250,000 miles on it in about 7 years, so obviously most miles were highway, and it’s average speed is mid 20’s. The time you spend at stoplights, waiting in line at drive throughs etc really kills the average speed.

But assuming it’s average speed was 25 mph, at 250,000 miles, thats 10,000 hours and it doesn’t burn a drop of oil and as you say 250,000 miles is very common.

It depends on where you live. If you are in an urban area, you are going to have a lot lower average speed. I looked up the average speed on Google for more open suburban and country type areas. That’s 45. I can certainly imagine driving around some traffic where you are from, you would get 25 mph.

That’s 125,000 miles with your 25 mile an hour speed. At 5000 hours on the engine. Even better.

Lastly I might disagree with one thing. I don’t think there’s a big difference between using a diesel truck engine and a marine diesel engine of the same size. Aircraft, yes. Maybe that’s different. But the marine diesel you’re going to run at 2200 RPM or something all the time. That’s just like highway miles. Same thing that my diesel truck runs at when I am going 80. It’ll do that all day long. Or you can back off a little bit and run at 1800. I think that somewhere around 60 miles an hour on the truck.

Now the part that I disagree with is about the intensity of the use. In a motor vehicle, you are winding that engine out all the time. You are hitting hi RPMs like you never would with a propeller. With a propeller, you are just sitting at a nice steady highway speed basically. That’s the best possible scenario for an engine. Rather than idling it half the time and then punching it half the time. Like motor vehicles require.

[kenbo]

This may only confuse the issue further but many OTR truck diesel engines makers have shifted the metric for maintenance and overhauls from hours to amount of fuel burned.

Hours on the clock can be and often is a misleading measure. But if you have historical records of fuel purchased/burned you have a very accurate picture of the work the engine has performed over the service time period.

In my opinion hours is not very revealing. There have been some excellent suggestions made in earlier posts about how to evaluate a used engine and I vote to include an oil analysis as long as you know when it was changed and with what brand/type of oil.

[a64pilot]

You will find that many, many people are of the impression that you need to run a small Diesel at 3,000 or higher RPM. Not all that many run them at half speed like I do at 1800.
That has something to do with how long the same engine in the same boat will last two different owners.
Just like some will change oil at 250 hours and a few will at 100 hours.
Most will religiously change oil on a new engine on schedule but not so much on an old one, and the new one doesn’t need it as often as it has less blow by and the oil stays clean longer, the older the motor, the more blow-by and the more frequently it needs it’s oil changed, but that’s not often what happens.

Your looking at average speed limits, not average speed. We ran most of the mileage in our Prius at 70 mph speed limits and most often ran the limit, and still only averaged 25 mph, you spend more time than you realize in traffic and stoped at lights etc than you realize.
We averaged over 30,000 miles a year and to do that and not be a delivery driver etc. you have to be mostly on the highways.

[a64pilot]

Originally Posted by Chotu

Now the part that I disagree with is about the intensity of the use. In a motor vehicle, you are winding that engine out all the time. You are hitting hi RPMs like you never would with a propeller. With a propeller, you are just sitting at a nice steady highway speed basically. That’s the best possible scenario for an engine. Rather than idling it half the time and then punching it half the time. Like motor vehicles require.

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.

[mvweebles]

Doesn't really apply to small sailboat engines, but the large diesel builders rate their engines for use. Tempting to say "I want the top rated one" that is rated for continuous usage at top-output (WOT) 5000-8000 hours/year but that would probably cause the engine undue wear and the owner undue expense.

MARINE ENGINE DUTY RATINGS

[MAJICDAN]

Most marine hour meters only go to 9999 like the four cylinder Perkins.
My 6.354 Perkins hour meter has one more digit.
I still have the original motor so I am able to register it as an antique in Florida.

[Cheechako]

Originally Posted by Searles

A verry strange statement ,as a diesel machanic with over 50yrs in the marine trade ,a shipwrights boatbuilder ,trade trained qualified diesel fitter ,mechanic ,I am verry interested where this sweeping statement is based ,have seen small twin Volvo penta ,driving an irrigation pump,running like a clock at 24k hrs no electrics hand start ,also a air cooled lister 3 cyl gen set running for 9 yrs with verry little maintaince,and an 8l3 Gardner in an 80 ft trawler at 90k hrs still strong ,. Maybe some small turbo charged highly stressed poorly maintained engines will have a short life ,look after them and they will look after you .,i

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.

[Cheechako]

Originally Posted by mvweebles

Doesn't really apply to small sailboat engines, but the large diesel builders rate their engines for use. Tempting to say "I want the top rated one" that is rated for continuous usage at top-output (WOT) 5000-8000 hours/year but that would probably cause the engine undue wear and the owner undue expense.

MARINE ENGINE DUTY RATINGS

Exactly, and they change the RPM by rating often also. A recreational engine may be rated at 3600 rpm and an industrial use one at 2400 rpm.. same engine. Which I have stated on this forum many times in the "you must run your diesel at near highest rated rpm" arguments.