Montemar
Active member
For how long will a diesel engine produce its rated power if it has been maintained and still works well? Is there a slow decrease in efficiency with hours?
Engine longevity
- Thread starter Montemar
- Start date
Rappey
Well-known member
Some Mercedes diesels reach full power around 80- 100,000 miles ! ?
I'm not sure you will notice it reducing power unless there is something wrong but then it becomes difficult to start.
My boat engine is 56 yrs old and had a rebuild in 1983. Still runs great.
I'm not sure you will notice it reducing power unless there is something wrong but then it becomes difficult to start.
My boat engine is 56 yrs old and had a rebuild in 1983. Still runs great.
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Portofino
Well-known member
Manufacturers tend to publish rated power with caveats regarding how much time in a typical cycle at what load .
ie 100 % loads for [ insert hr (s) ] every ( insert another time number ).
Having said that many American boat captains from personal experience suggest running all day @ 80 % load extends longevity .Talking pro sport fishers racking up 1000 s of hrs .A rebuild @ 8000 hrs is better than one @2500 hrs .Thats how they make them last to the higher figure ........running below 80:% load
The load depends on fouling and weight etc .Not all marine engines have access to load data .
As a rule of thumb for those who are unable to directly read it they say the fuel used can be a rough guide so set the rpm no more than 80:% of its max consumption.....if you can figure that out ?
ie 100 % loads for [ insert hr (s) ] every ( insert another time number ).
Having said that many American boat captains from personal experience suggest running all day @ 80 % load extends longevity .Talking pro sport fishers racking up 1000 s of hrs .A rebuild @ 8000 hrs is better than one @2500 hrs .Thats how they make them last to the higher figure ........running below 80:% load
The load depends on fouling and weight etc .Not all marine engines have access to load data .
As a rule of thumb for those who are unable to directly read it they say the fuel used can be a rough guide so set the rpm no more than 80:% of its max consumption.....if you can figure that out ?
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Portofino
Well-known member
A leak down test would tell you if the cylinders are maintaining compression , if you think there’s been a insidious loss of power over your ownership period .
BruceK
Well-known member
If maintained then the short answer is no. You'll lose power on compression, injectors, pump, boost etc. But if maintained, serviced and replaced there is no reason to loose power.
oldgit
Well-known member
Some time ago programme on TV poss. Top Gear ?
They put a selection of older cars on a rolling road to compare original maunfacturorHP claims when new against actual output on the rolling road.
All were down, some up to15-20 % down from new. ???
Idea was find what tuning add ons gave most bang, for your buck.
The pair of 40A in my Princess 33 @ 4000 hours were definately down from the claimed 135 HP.
They put a selection of older cars on a rolling road to compare original maunfacturorHP claims when new against actual output on the rolling road.
All were down, some up to15-20 % down from new. ???
Idea was find what tuning add ons gave most bang, for your buck.
The pair of 40A in my Princess 33 @ 4000 hours were definately down from the claimed 135 HP.
Rappey
Well-known member
They were petrol engines though. ? Some car diesels are capable of huge mileage.
Momac
Well-known member
In a leisure boat lack of use is almost certainly the greater threat.
BruceK
Well-known member
The question though includes maintained. If you are down on power something has worn. Given wetliners and cheap engine rebuilds, for example KAD @5k for the rebuild kit, there is actually no reason why the engine cant last a lifetime and continue to deliver full rated HP. You'll find your turbo was down, injectors poor or something to account for your loss of power but unless they are making lower calorific fuel then....
Portofino
Well-known member
Turning the Q around how do you shorten a maintained marine diesel life ?
With maintenance we need to classify a few things .
Are we talking manufactures timed schedules, which I think we are , or Bruces idea of throwing parts at it for ever and a day
.Playing whack a mole ?
Assuming normal manufacturing timed schedules you can prematurely loose power by overloading them which results in soaring EGTs .
The problem with sustained elevated EGTs is the exhaust valve mushroom .It’s insidious, it’s not a Big Bang scuse the pun .
They gradually loose best seating from a hermetic pov and pressure in the cylinder thus power gradually reduces as time and continuous overloading goes on .
Don’t confuse this with ring wear which leads to easily detectable blow by in the bottom end .Or oil analysis will pick this up .
Remember talking “ maintained “ which in inc annual lub changes irrespective of low hrs .
A lot of boats need “ tight wire “ to get them up planning , more so with additional weight .
A lot were on the edge power wise when new offered in a lower Hp cheaper D 4 as well as proffered D6 for example.
Given a choice hunt down the bigger engine spec version so they never have to be run at searing EGTs .
With maintenance we need to classify a few things .
Are we talking manufactures timed schedules, which I think we are , or Bruces idea of throwing parts at it for ever and a day
.Playing whack a mole ?Assuming normal manufacturing timed schedules you can prematurely loose power by overloading them which results in soaring EGTs .
The problem with sustained elevated EGTs is the exhaust valve mushroom .It’s insidious, it’s not a Big Bang scuse the pun .
They gradually loose best seating from a hermetic pov and pressure in the cylinder thus power gradually reduces as time and continuous overloading goes on .
Don’t confuse this with ring wear which leads to easily detectable blow by in the bottom end .Or oil analysis will pick this up .
Remember talking “ maintained “ which in inc annual lub changes irrespective of low hrs .
A lot of boats need “ tight wire “ to get them up planning , more so with additional weight .
A lot were on the edge power wise when new offered in a lower Hp cheaper D 4 as well as proffered D6 for example.
Given a choice hunt down the bigger engine spec version so they never have to be run at searing EGTs .
westernman
Well-known member
It is possible that new they were already 15-20% down when they came out of the factory.
There used to be a lot of wildly optimistic marketing claims made for some engines.
Portofino
Well-known member
There’s a thing between the wheels and engine commonly called a gearbox in a car .The car version has selectable ratios .
Boat equivalent version has only one gear top .
So you want to drive over the Himalayas in your super long long lasting fully maintained car with a diesel ?
It won’ t be always in top gear , you will ease the load with the gearbox , indeed the load will vary wildly even reducing as you coast on the down hill sections .
Now the boat , bit of fouling hull and props , bigger tender , davits , extra 1 m open array scanner on the new bigger custom built radar arch .You have knocked the galley about added a dish washer + freezer .
12 pax today for a day trip on the Cornice 31 .Unlike the Himalayas it’s pancake flat .What could possibly go wrong ?
Think about those poor old VP 40;B s as the owner try’s to demo 24 knots because the Internet boat test said so .
Once up ( if it ever gets up ) the throttles are pinned . Yet you used the gear box in the car .
” But it’s only done 800 hrs “ Yep !
volvopaul
Well-known member
Your engines still not making 3900 ?
Fully empty the boat contents and have the hull and stern gear cleaned then go and test it , even running with the canopy off will help reduce wind age .
Montemar
Active member
They need to make 3900 in the normal cruising state. Quite how a magazine article said 22 knots was achievable when the boat had 90% fuel, 70% water people etc. and weighed 7.5 tons with engines delivering 180hp is ludicrous. Mind you how many journos know what they are talking about! I am getting the props re-pitched so I can reach 3900rpm at whatever speed it gives me with max fuel, 50% water and a well stocked drinks cupboard. The re-pitch will be relaated to the most correct assessment I can make of the boat's weight, my current props are pitched for a boat weighing 7.5 tons so I am overpropped. I am happy that the engines are running well. I'll let you know in a months time.
Farmer Piles
Well-known member
The kindest thing for a diesel engine is for it to be worked hard all it;s life from new. As mentioned above, working at say, 80%, not flogged to death. Nothing reduces output quicker than light running in a diesel engine.
Last year the diesel engine in our self propelled sprayer decided that it had had enough. It went from a tappet type ticking noise to a drummer with hammers on a anvil sound - it was hideous. I didn't think that i was going to make the 400 yards back to the yard. It had done 10 000 hours but you can expect over 15 000. We suspect a broken crank or a failed balancer shaft.
Anyhow, back to the point; we put a brand new engine in - a John Deere 4.5 litre turbocharged - and now that it has done 100 hours of running in you can feel that it is probably 20-30% more powerful than the old engine.
I would say just the wear and tear on the old one - the turbo, injector pump, valves, injectors, compression, wear in the bearings, etc.. None of them too bad on their own but they all add up.
So yes, I would expect performance to drop with time and use.
Last year the diesel engine in our self propelled sprayer decided that it had had enough. It went from a tappet type ticking noise to a drummer with hammers on a anvil sound - it was hideous. I didn't think that i was going to make the 400 yards back to the yard. It had done 10 000 hours but you can expect over 15 000. We suspect a broken crank or a failed balancer shaft.
Anyhow, back to the point; we put a brand new engine in - a John Deere 4.5 litre turbocharged - and now that it has done 100 hours of running in you can feel that it is probably 20-30% more powerful than the old engine.
I would say just the wear and tear on the old one - the turbo, injector pump, valves, injectors, compression, wear in the bearings, etc.. None of them too bad on their own but they all add up.
So yes, I would expect performance to drop with time and use.
BruceK
Well-known member
Bruces idea of throwing parts at it for ever and a day
My parts are cheap, I can afford to, so why not. My engines will outlive me and still generate max power. You live in fear of EGT, me, I give it welly. It's a sports cruiser.
Portofino
Well-known member
No fear just sensible management of the longevity question which I thought this thread was about ?
I,am not the only one who manages the EGTs / loads btw .
Advice is free and readily available on every marine mobo engine / power forum section as I said contributes by professionals who rack up 1000 s hrs / annum .Copy them it works .
BruceK
Well-known member
The question was
The answer is no. Even given your EGT's a maintained engine doesn't just run on fubar exhaust valves. Any right minded person would replace and reseat them. It's not exactly an onerous nor for that matter, expensive job.
There are those that do minimal maintenance and if it's painted right and looks the part, starts and goes, that will leave well enough alone until there is a breakage. Without doubt under the wasn't maintained classification then one would expect a gradual power drop. The defining point was maintenance. And really, there is so much angst and fear generated on this forum about engines precisely because most engines are not optimally maintained.
Your EGT doomsday placard doesn't bother me too much either to be honest. I am in the camp that you'd really have to abuse the boat to develop a problem there. Nobody is going to fit an engine into a boat that is not fit for purpose. That is not to say EGT is a concern, it's just not a Damocles sword. I do not fear my engine exploding just because I gave it some welly. There would be a helluva lot of angry boat owners at the dealers if this was a common occurrence. I dare say it's a very uncommon occurrence.
The answer is no. Even given your EGT's a maintained engine doesn't just run on fubar exhaust valves. Any right minded person would replace and reseat them. It's not exactly an onerous nor for that matter, expensive job.
There are those that do minimal maintenance and if it's painted right and looks the part, starts and goes, that will leave well enough alone until there is a breakage. Without doubt under the wasn't maintained classification then one would expect a gradual power drop. The defining point was maintenance. And really, there is so much angst and fear generated on this forum about engines precisely because most engines are not optimally maintained.
Your EGT doomsday placard doesn't bother me too much either to be honest. I am in the camp that you'd really have to abuse the boat to develop a problem there. Nobody is going to fit an engine into a boat that is not fit for purpose. That is not to say EGT is a concern, it's just not a Damocles sword. I do not fear my engine exploding just because I gave it some welly. There would be a helluva lot of angry boat owners at the dealers if this was a common occurrence. I dare say it's a very uncommon occurrence.
petem
Well-known member
I agree. The forums and FB groups are hardly awash with tales of knackered KAD engines and I imagine many have been driven hard with less than fastidious maintenance.
Dino
Well-known member
Does your Broom 33 have trim tabs or a fixed tab? My Crown has twin 148hp VP TAMD40A’s and a set of fixed tabs the full width of the transom. Mine tops out at around 17.5 knots at WOT. I heard that the fixed tab was added to extend the hull length and increase the planing surface.
Is there a design issue with the 33 with it being a short and wide boat? From my years of sailing, there was always a thing with having large flat sections aft to help surfing down waves and planing. Shorter heavier boats would surf but not plane. Also, I had a 12ft rib with loads of power(25hp 2 stroke) and I always had to lean forward over the console to get it to plane. I think a lot of boats that are short relative to their width and weight struggle to get over the hump.
Is there a design issue with the 33 with it being a short and wide boat? From my years of sailing, there was always a thing with having large flat sections aft to help surfing down waves and planing. Shorter heavier boats would surf but not plane. Also, I had a 12ft rib with loads of power(25hp 2 stroke) and I always had to lean forward over the console to get it to plane. I think a lot of boats that are short relative to their width and weight struggle to get over the hump.
