Car/boat engine life - how to calculate ???

[Salty John]

It's an impossible question to answer, as others have said.
For small diesels in boats, taking into account the intermittent use, use at low temperature, environment etc. you might as well use all up engine weight in pounds divided by normally consumed HP, the answer is years before major rebuild. As accurate as anything else.

 

[MapisM]

I must admit that I'd never thought of engine life in terms of total fuel burn but it makes absolute sense.

Actually, I'm told that on big industrial diesels even the maintenance schedule is based on the amount of fuel burnt (maybe LS can confirm or correct me if I'm wrong).
Are construction machines engines based "only" on hours, as with pleasure boats?

 

[Deleted User YDKXO]

Are construction machines engines based "only" on hours, as with pleasure boats?

Yes in my business we refer only to working hours because its easy for people to understand and our machines tend to be used in the same way by all users so its valid to compare only hours. But the engines are used differently to boats. Instead of the operator varying engine rpm according to requirement, the operator sets the engine rpm at a fixed speed, usually maximum goverened speed, and the computer controlling the hydraulic system manages the functions of the machine so as not to overload the engine

 

[MikeJ42]

As a rule of thumb a typical modern mid range diesel putting out 60 HP per liter maximum and is between 5 and 7 liters total displacement will burn around 25,000 gallons of fuel before the measurements to do with blow-by, oil consumption, compression, etc., would dictate a rebuild. CAT used to publish a durability figure for the 3208 of 25,000 gallons regardless of rating or duty cycle. Forget the engine displacement, it fits into this node, therefore it becomes logical that the 320 Hp rating has higher durability factor expressed in hours than the 425 Hp rating.

So my D6 435HP engines are gonna last about 1yr considering you can can get D6 310HP

 

[Tranona]

Personally I think a great deal of marine engine stuff is money for old rope. I know what a certain big car manufacturer does to turn its automotive engines into marine ones and the basics are to strip most of the expensive stuff off and then mark the price up by an eye-watering percentage.

If it were that easy, I wonder why VW have just stopped their marine engine business. Second time in their history they have failed to make it work commercially.

 

[Chris_d]

So my D6 435HP engines are gonna last about 1yr considering you can can get D6 310HP

I am sure I remember a quote when one of the early Volvo KAD44's suffered a now known fault of valve train failure after a very short period of 1 year, Volvo said "what do you expect if you do that many hours in a year" I think it was just over 150hrs which is of course outside the expected typical leisure use of 50-100hrs

 

[Fire99]

If it were that easy, I wonder why VW have just stopped their marine engine business. Second time in their history they have failed to make it work commercially.

Well I can't speak for VW but someone very close to me (not physically ) was directly involved in the whole Automotive - Marine engine malarkey for a big manufacturer and that was how it worked.
I wouldn't be surprised that one of the biggest costs is the labour involved in removing the 'automotive kit'. Economy of scale and all that.

 

[Questor]

Actually, I'm told that on big industrial diesels even the maintenance schedule is based on the amount of fuel burnt

This is how the service schedule "lights" that BMW have been using on their cars for years work, on both petrol & diesel engines. Same principle.

 

[MapisM]

Doh! I never thought about it, but it does make sense, with modern engines whose ECU always knows the amount of fuel burnt.
Probably it's not just a BMW thing?

 

[Latestarter1]

Very informative as usual latestarter1. I must admit that I'd never thought of engine life in terms of total fuel burn but it makes absolute sense. What about number of cold starts? Does this have a significant effect on engine life? I was told in the past that engine life was a function of working hours and number of cold starts but maybe this is not entirely correct

Good rule and actually bakes into the equation real well. As engines start in over fuel condition and burn more fuel before coming up to temperature.

The trick is hiding the smoke caused by excess fuel on start up on modern engines.

 

[Latestarter1]

So my D6 435HP engines are gonna last about 1yr considering you can can get D6 310HP

Have not got an old 310 spec sheet to hand, however current D6-330 60 Hp/litre burns around 52 litres/Hr @ 3200. D6-435 79 Hp/litre burns 62 litres/Hr @ 3200.

Given the extra power is costing you extra 10 litres/Hr Gonna take you a long time to eat up your 25,000 gallons even at 62 litres/Hr

 

[Assassin]

Cold starts do have an affect on engine life as they consume more fuel while warming, and they are designed to work within an operating temperature, as is oil and anything else to be at its optimum.

Take an average industrial engine on a generator, once started it will run for the working day, it has only one cold start and once warm is running at its optimum working conditions. Alternatively it could be started once and run for several days or weeks before stopping, therefore cold starts are not really a factor.

Take the same engine in an excavator, it may work a shorter working day, but be started once in the morning and run all morning, stopped at dinnertime, then hot started again to work all afternoon.

Compare this to an average marine variant of the same engine, it has very considerable variables, it may be that the owner is the poser type owner who has a boat for show and remains permanently on the berth. This means many cold starts and virtually no running, alternatively an enthusiastic owner may run their engines at every opportunity to get out in their boat to get as much sailing pleasure as possible.

In comparison to the former variants of the engines, both marine variants have a lot of cold starts and it becomes a variable or factor in engine life, particularly as few boaters use their craft all year round. We can also see that the former industrial variants applications means they have to work to earn their living and generate a profit, pleasure boats do not, and unlike the industrial engines they are not working every day for most of their lives. It is these long periods of inactivity which can create more issues.

 

[jfm]

I have written about this on a number of occasions, however requires some understanding of basic definitions as they are often confused:

Durability. Simply life of engine before blow by and other measurements dictate a rebuild.

Reliability. Generally but not in all cases mission disabiling failure of hang on components. The cause can be poor design or manufacture, or the most common simply 'marine aging'.

To keep life simple I assume OP is referring to engine durability.

All engines wear in relation to the power they are asked to develop, power equals fuel burned. This is the key parameter that is used to estimate engine durability.

As a rule of thumb a typical modern mid range diesel putting out 60 HP per liter maximum and is between 5 and 7 liters total displacement will burn around 25,000 gallons of fuel before the measurements to do with blow-by, oil consumption, compression, etc., would dictate a rebuild. CAT used to publish a durability figure for the 3208 of 25,000 gallons regardless of rating or duty cycle. Forget the engine displacement, it fits into this node, therefore it becomes logical that the 320 Hp rating has higher durability factor expressed in hours than the 425 Hp rating.

Heavy duty engines between 8 and 12 liters putting out around 40 HP per liter are at least 2 but more often over 3 times that. I would expect 65,000-85,000 gallons of fuel consumption on a marine engine in commercial service where the cruise HP is limited to about 30 HP per liter. California is a big re-power market, has large but fast declining population of Detroit motors for which you receive grant funding to replace. As a result there is plenty of documentation of commercial rated 8.3 litre Cummins 350C marine engines burning at least 80,000 gallons long before blow by limit is reached.

You will find many a stories of 3-5 liter G drive engines with 20,000+ hrs and are still running strong..Guess what, the generator engine is averaging .62 to1.25 gph therefore the logic still applies.

Of course, all these estimates of total fuel burn mean nothing if the engine has been running above its designed propeller/ load curve or ??? There are so many things in a boat that affect "practical" engine durability which is why I included 'reliability' at the beginning, and being realistic, the total amount of fuel that an engine has consumed rarely is the factor that causes the engine to be replaced or rebuilt in a recreational application.

Where leasure engine use is typically between 100 and 500 Hrs per year 'marine aging' and operation outside their design envelope kills engines off long before we have burned off our £160,000 worth!!!!!.

Hi LS. Thanks, all very informative and engineeringly logical. The Cat service schedules that came with my motors are basically fuel-burnt based

However your maths isn't right i think. You need to add a factor for size of engine. If you take an inline 6 cyl motor doing 50hp/litre and durability to excess blow-by (say) 70,000 gallons, then you take same motor and engineer it to V12, AOTBE except for upsizing the crank main bearings, it needs the same rebuild at 140,000 gallons

My Cat C32 which are 50hp/litre will need rebuild at say 40,000 gallons, if I interpolate your numbers. They burn 35 gallons an hour, so that's a durability in the order of magnitude 1000 hours, which aint right. (I hope...)

Your numbers are right, but you need to add a "per hp" or "per litre" factor or something to the fuel burns

 

[BartW]

My Cat C32 which are 50hp/litre will need rebuild at say 40,000 gallons, if I interpolate your numbers. They burn 35 gallons an hour, so that's a durability in the order of magnitude 1000 hours, which aint right. (I hope...)

I came to a similar calculation on my 1100HP MAN engines, they burn 150l/hour each,
having 2000hrs on the counter they are well over their expected live cycle then ?

must be missing a "per / engine volume" element in the equasion I believe

(MAN D2848-401 swept volume is 14.6l)

 

[rafiki_]

The other variable is duty cycle, although there is some correlation to fuel mass flow rate. I worked on several high performance vehicle programmes, and in order to get the right validation programme, we needed to know the duty cycle, so we measured the road load data, including the ammount of time spent at or near max power. A B category normally aspirated engine spent 65+% of its time at max throttle on our test cycle. The C cat (Focus size) turbo spent less than 20% at max throttle. The prevailing traffic versus the usuable performance meant that you spent a lot of time waiting to overtake slower stuff if you get my drift. This allowed us to set the duty spec for a 300,000 km life, serviced at 30,000 km intervals, with no major failures.

When you relate this to a planing boat, when on the plane, it spends much of its life at 70%+ max throttle.

However, if the marine engine is truck based, this is designed to spend a lot of time at or near max throttle, unlike a car.

Moral of the story is if car based, the engine is likely to wear out quicker in a planing boat, then if truck based, hence the D3 woes.

River craft have a much lower duty cycle, so hire craft have very low powered non turbo engines that last huge engine hours.

If you then factor in maintenance etc, you have a huge number of variables.

I live mostly on a river, with a twin engined diesel, with engines car based, up spec'd compared with the car. No problem for me, but I know that when I go to sea and plane, I must throttle back for extended periods, otherwise I will rapidly increase the wear rate.

 

[Latestarter1]

The other variable is duty cycle, although there is some correlation to fuel mass flow rate. I worked on several high performance vehicle programmes, and in order to get the right validation programme, we needed to know the duty cycle, so we measured the road load data, including the ammount of time spent at or near max power. A B category normally aspirated engine spent 65+% of its time at max throttle on our test cycle. The C cat (Focus size) turbo spent less than 20% at max throttle. The prevailing traffic versus the usuable performance meant that you spent a lot of time waiting to overtake slower stuff if you get my drift. This allowed us to set the duty spec for a 300,000 km life, serviced at 30,000 km intervals, with no major failures.

When you relate this to a planing boat, when on the plane, it spends much of its life at 70%+ max throttle.

However, if the marine engine is truck based, this is designed to spend a lot of time at or near max throttle, unlike a car.

Moral of the story is if car based, the engine is likely to wear out quicker in a planing boat, then if truck based, hence the D3 woes.

River craft have a much lower duty cycle, so hire craft have very low powered non turbo engines that last huge engine hours.

If you then factor in maintenance etc, you have a huge number of variables.

I live mostly on a river, with a twin engined diesel, with engines car based, up spec'd compared with the car. No problem for me, but I know that when I go to sea and plane, I must throttle back for extended periods, otherwise I will rapidly increase the wear rate.

Having used DCM,s for heavy duty diesel engine development I follow your % throttle arguement however everything you are saying boils down to % engine load therefore fuel burned.

Likewise when you talk about your own engines with respect I would suggest you are looking at it the wrong way. Operation at WOT does not rapidly increase wear, it increases in direct ration to the rate of fuel burn which is engine life. Now as usual the BIG however, a marine engines 'rated' power or max throttle in pleasure duty is strictly for the birds.

We are only concerned about continious duty in the the real world. Every engine manufacturer varies slightly with their rating definitions which is real confusing unless you are a spec sheet geek. Operation at WOT or 'max throttle' as you put it can be as little as half an hour out of every six. I did some work back in 2008 which suggested then that pulling 35 Hp/liter or 30/50% engine load seemed to represent maximum CONTINIOUS duty regardless of engine colour up to a maximum of 500 Hrs/Year.

Believe that we are kind of talking the same language until you mentioned the Volvo D3, then you commit the cardinal sin of confusing durability with reliability.

A properly designed diesel engine properly applied should just wear out in a direct relationship with the load placed on it, once again measured as fuel burn. A poorly designed engine may suffer mission disabling events on the same duty cycle for example head gasket failure many times before it gets to TBO (life to overhaul). The poorly designed engine has the same durability but not the same level of reliability.

Has anybody ever worn a D3 out when operated it in line with Volvo duty cycle no! Problems with D3 appear to relate to suitability of base engine design for the duty cycle and competence of the marinisation. These are 100% reliability issues.

 

[MikeJ42]

So how do modern high revving motors fit into all this? My D6's (435HP) rev to 3500rpm whereas most equiv size/power rev to 2500/2800. This always concerned me slightly. Are the industrial variants just rebadged and limited to 2500rpm?

 

[rafiki_]

Having used DCM,s for heavy duty diesel engine development I follow your % throttle arguement however everything you are saying boils down to % engine load therefore fuel burned.

Likewise when you talk about your own engines with respect I would suggest you are looking at it the wrong way. Operation at WOT does not rapidly increase wear, it increases in direct ration to the rate of fuel burn which is engine life. Now as usual the BIG however, a marine engines 'rated' power or max throttle in pleasure duty is strictly for the birds.

We are only concerned about continious duty in the the real world. Every engine manufacturer varies slightly with their rating definitions which is real confusing unless you are a spec sheet geek. Operation at WOT or 'max throttle' as you put it can be as little as half an hour out of every six. I did some work back in 2008 which suggested then that pulling 35 Hp/liter or 30/50% engine load seemed to represent maximum CONTINIOUS duty regardless of engine colour up to a maximum of 500 Hrs/Year.

Believe that we are kind of talking the same language until you mentioned the Volvo D3, then you commit the cardinal sin of confusing durability with reliability.

A properly designed diesel engine properly applied should just wear out in a direct relationship with the load placed on it, once again measured as fuel burn. A poorly designed engine may suffer mission disabling events on the same duty cycle for example head gasket failure many times before it gets to TBO (life to overhaul). The poorly designed engine has the same durability but not the same level of reliability.

Has anybody ever worn a D3 out when operated it in line with Volvo duty cycle no! Problems with D3 appear to relate to suitability of base engine design for the duty cycle and competence of the marinisation. These are 100% reliability issues.

I'm sorry but I don't confuse durability with reliability, I don't think I mentioned either of them. The point I was trying, but maybe failing to make is that engine's designed properly, are lifed for a specific duty cycle, assuming the parameters are properly understood byt he designer. The base D3 engine block was designed for a light duty vehicle, base engine desiggned by AVL, head and ancillaries by Ricardo, for various Volvo car applications. It was not designed for continuous operatin at 70%+ of its max peprformance, as in a planing boat. Truck engines are ldesigned to be used at 70%+ of their available performance, most of the time, and havew a much lower rev band, and trailing torque curve to help them with inclines. Light duty engines are designed for performance and refinement. Horses for courses.

My own engines are the 1.7l Isuzu's used in various Vauxhall/Oopel light duty applications. When the performance is used in moderation, these are good little engines. With continuous WOT they have a fairly rapid failure rate, generally no 3 piston, where the cooling is not so effective.

I have lived the reliability v durability argument in the car world, where some people insist on doing huge milages in test cars. However you get the "Trigger's Brush" syndrome. The car does 120,000 miles, but having used a couple of engines and gearboxes, etc. Job done, achieved 120,000 miles on a car, but proved nothing.

 

[Assassin]

There is another consideration which is overlooked, this is the multi use, single designed engine, this is basically one engine designed for a multitude of uses and power ratings.
Such engines are becoming more popular, it may be that a single engine may be used in a boat (working or pleasure) site plant, generators, trucks, and even as water pumps, and the one engine will have multiple power ratings and load cycles.
This creates many issues and confusion among many people as they do not understand duty cycle and power rating, and the correlation between the two in multiple applications.

 

[Latestarter1]

I'm sorry but I don't confuse durability with reliability, I don't think I mentioned either of them. The point I was trying, but maybe failing to make is that engine's designed properly, are lifed for a specific duty cycle, assuming the parameters are properly understood byt he designer. The base D3 engine block was designed for a light duty vehicle, base engine desiggned by AVL, head and ancillaries by Ricardo, for various Volvo car applications. It was not designed for continuous operatin at 70%+ of its max peprformance, as in a planing boat. Truck engines are ldesigned to be used at 70%+ of their available performance, most of the time, and havew a much lower rev band, and trailing torque curve to help them with inclines. Light duty engines are designed for performance and refinement. Horses for courses.

My own engines are the 1.7l Isuzu's used in various Vauxhall/Oopel light duty applications. When the performance is used in moderation, these are good little engines. With continuous WOT they have a fairly rapid failure rate, generally no 3 piston, where the cooling is not so effective.

I have lived the reliability v durability argument in the car world, where some people insist on doing huge milages in test cars. However you get the "Trigger's Brush" syndrome. The car does 120,000 miles, but having used a couple of engines and gearboxes, etc. Job done, achieved 120,000 miles on a car, but proved nothing.

I was tending to agree with you until you made the statement regarding the Volvo D3 engine. Sadly I now perceive that we are now further apart. In order to design engines you have to understand the concept of duarbility Vs reliability.

The politics of who was behind the design of the Volvo D5 engine have little relevance, Ford Europe funded it and Ricardo would have got the whole job had they not have fallen out with Ford over project Puma.

If we are considering LDA (Light Duty Automotive) diesel engines of ANY colour attempting to pull a 70% continouus duty out of it is not viable, in my original post I stated 30/50% as CONTINUOUS duty. The duty cycle is the key ingredient. One of the major issues with LDA engines is the use of swing vane VG turbochargers. Operation at or around peak torque creates soot, swing vane turbochargers stick for a living if subjected to this environment. Couple the use of fragile turbo machinery with a very poor marinisation and I stand by my point that nobody has ever taken a Volvo D3 out to its B50 life, TBO or life to overhaul, whatever you wish to call it. The fact of the matter is that the engine is brought to its knees by reliability issues, or operation outside of the design envelope.

Operation outside design limits brings me neatly on to your little 1.7 Isuzu motors, once again lack of durability Vs reliability thinking is leading you to come to the wrong conclusions.

#1 issue with the engine was fluffy application directions issued by Mercruiser. Engines picked up pistons for a pastime and motor developed a stinking reputation. Upon the creation of CMD Cummins picked up responsibility for the problem child. Cummins re wrote the spec sheet in a far more clear and concise manner to ensure motor was not mis-applied. The problem with the waste gate corroding and sticking causing excessive boost was never addressed,
simply adding checking of the waste gate to annual shedule is all that would have been required.


I purchased a Humber RIB along with my son, it had Mercruiser 120 with blown piston. Boat was over propped as a result of wooly literature. We rebuilt the engine, changed the props and maintain the waste gate linkage at the beginning of every season, ten years on the old girl still performs faultlessly. Chasing down #3 piston cooling was not the answer you have ended up looking at the fuse, every engine has a fuse, and not the true cause of the failure.

'Truck engines are ldesigned to be used at 70%+ of their available performance, most of the time'
No no no, sorry but you are completely wrong! A typical 11 to 13 litre heavy duty diesel engine developing around 420 Hp at 1,900 rpm rated in 44 Tonne operation geared to operate at around 1,500 rpm at 56 mph is operating at nothing like 70% load factor in top gear. We could not get anywhere close to that figure in Finland at 62 Tonnes operation.

This has got me on my old hobby horse, engine loading and understanding how the engine is designed to operate is paramount to long engine life.

Proper propping of a vessel cannot be stressed enough, will typically only come some time after the vessel has settled in to "its" normal running conditions, and then only with an understanding by the vessel operator of the engine's operating requirements published by the engine manufacturer. But in addition to that, is the understanding that adding some conservatism, "PRUDENT OPERATION", to these operating conditions by not running "on the edge" of these requirements, can mean the difference between 500 hours between catastrophic failures, and 5000 hours of relatively trouble free operation for the same engine.

The easiest and most proven way to accomplish this "conservatism" is by propping the vessel at full working weight to rated RPM plus AT LEAST 100 rpm, unless we are dealing with an electronic engine. When using these types of diesels that develop upwards of 50-60 HP per liter. It's actually very simple when you understand the whole picture of vessel operation and all of the variables that occur over time.

Moving on to MikeJ42's question regarding rated speeds. Producing more power at a higher rated speed within the bounds on the engine design envelope makes total sense as this reduces critical internal engine pressures. The bmep (brake mean effective pressure) of most turbocharged diesel engines is in the range of 14/18 bar pressure. If I was developing an engine and wanted to increase the power by say 10% and had a choice or increasing rated speed or bmep, keeping the bmep constant and increasing rated speed would be my obvious path.

We used to be paranoid regarding piston speed, CAT set the piston speed record for heavy duty diesel engines with the C18, much shaking of heads as it took a heavy duty engine into high horsepower engine territory, typically Cummins K19 power node, with a far less expensive and less bulky package. Early C18 blocks in RNLI trials had some problems however major revision of the block resolved the issue, piston speed has never proved to be a problem despite much muttering.