Why Do Engines Need Replacing?

[Thepipdoc]

It never ceases to amaze me the number of boats that have either had a complete engine replacement or have had major work carried out on them despite having done relatively few hours - i.e. 500 hours.
Whats the general consensus as to why this should be?
In this day and age surely engines are designed to run for many thousands of hours?

 

[Searush]

Use it or lose it!

Most boats are left for long periods in a hostile environment. They get very poor (if any) maintenance - at best new filters & oil change once a year & then neglect all season.

 

[Fire99]

Use it or lose it!

Exactly!

Since the dawn of the combustion engine, the biggest killer of an engine is leaving it sitting unused, closely followed by the 'Start up, Run for a few mins, Turn off' scenario.

Vary rarely do Marine engines 'wear out'. Sadly, alot like cars, people are attracted to low engine hours (miles) but in reality, if the rest of the boat has been maintained then a well used/ serviced engine should give excellent service.

I would offer a word of caution with the new breed of high output/lightweight turbo diesels since certain items like turbo's and fuel pumps may need to be treated to a certain degree as consumables.

 

[Kawasaki]

Yep, Searush has it.
Vessels are left idle for too long.
The enviroment is as My Learned friend put it, hostile.
They don't wear out per say.
The kinda rot and fester.
Then they don't function properly.
Lots of times its the marinisation bits that fail first then the rest of the lump can be affected.

Think about your car.
Gets used regularly
Gets serviced when it should or near enough!
Doesn't live in a salty air.
Salty air!
Ha sounds like a sea shanty.!
Sorry, mind drift not thread drift

One of the probs with boats is we aint got no radiator.
So on sea going vessels we use the sea to help keep the thing at the right temperature.

Sometimes I think to myself when peeps say 'I.ve just bought a 20 year old boat.
It's only got 300 hours on it'!(or similar)
Matey, thinks I
Be better if it had 3000 up it!

Its lack of use
Lack of correct maintenance
Salty stuff what knackers em.

I know about correct maintenance.

Cos I,ve been lax with mine and now I,m into big fixing
Talk about The Cobblers Shoes!
'Hits oneself wif a hammer on the Bonce'!

 

[Bajansailor]

I would agree with all of the above thoughts - the engine in our sailboat blew up this year with less than 1,000 hours of use (but 17 years old) - principally (I think) from a lack of use (and a philosophy of 'If it aint broke, dont fix it' applied too far - if I had stripped down the heat exchanger and oil cooler before re-launching her then it would probably be fine now).

Pal of mine here has a Yanmar diesel engine, only 10 years old, and 6,000 hours on the clock - in a sailing boat - and it still looks almost new, runs like a dream, has never needed any major attention.......

 

[Duster]

I think that most of it has been said,
Limited use with long periods idle
Irregular maintaince often by rather second rate mechanics
High revs
Hostile environment
Cooling systems designed by a mariniseing company as an afterthought rather than by the engine designer.
We used to run small / medium sized agricltural engines up to 10 to 12000 hours in 8 to 10 years in a dusty or corrosive environment (crop spraying) regularly, with few problems. Maintainance was an oil & filter change once a month and the head off / valves and injectors every 5000 hours. Most of our problems were with ancilories like alternators and water pumps. These engines were turbo' d but only reved to about 2400 running mainly at a constant 2000rpm. I suppose one of the reasons they lasted so well was that they were started in the morning ran 5 hours, stop for lunch, run another 5 hours.
regards mikej

 

[dpb]

With petrol engines it is often that the manifolds and or risers have rusted through, and because of the design, any water that gets into the 'dry' side ends up draining into the more expensive areas of the engine, ie cylinders and valve areas. I find it hard to believe that the cooling system can,t be designed so that when it fails it doesn't take the rest of the engine with it, especially as they can fail in as little as three years!

 

[oldgit]

"It never ceases to amaze me "

This should be heads up to future boaters buying todays(and yesterdays) power units.
Like it or not,all that high power being wrung out of those small blocks will come back and bite somebody further down the line.
In the never ending quest for power,lets be honest speed actually,longevity is being sacrificed.
Next time you are looking around in the boat listings,take note of the suprising number of modern boats which have had new engines put in after but a few hundreds of hours .

 

[rafiki_]

If on average a cars is used for 10,000 mules per year, at 30mph, then this is 330 hours per year.

My car does 20,000 per year, at 40 mph ave, therefore 500 hours, and is serviced once a year, generally oil and air filter. Nothing much more. The rest of the car needs a bit more like brake fluid/pads/aircon etc.

Car engines these days are designed to run for 200,000 mile before major rework, and truck engines 500,000.

My boat did 50 hours this year, and will get oil and filters, fuel filters etc and probably fresh coolant. The turbo will get a look at and oil up, and I'll also check the cam drive belt. Therefore I'm hoping for many years of happy and reliable boating...................

Neglect, especially to the heat exchanger is the most likely failure scenario.

 

[[2068]]

Like it or not,all that high power being wrung out of those small blocks will come back and bite somebody further down the line

That's not the only factor. Design flaws cause engines to go bang rather than any specific power to displacement ratio. No modern high-revving marine diesel is anything like a Gardiner: thank goodness, else none of us would get planing.

Instead, ask a Volvo Dealer how much it would cost if say a D4 or D6 were to drop a valve, and score the bore on one cylinder. What's that? The liners aren't replaceable? A New Engine???

 

[Duster]

Another problem may be that with marine being a small market, manufacturers can get away with design weaknesses that in a car or truck engine would totally kill its place in that market.

mikej

 

[oldgit]

" No modern high-revving marine diesel is anything like a Gardiner: thank goodness, else none of us would get planing"

Arr.... so this boat from ye olde prehistoric tymes be not planing then

 

[Chris_d]

If on average a cars is used for 10,000 mules per year, at 30mph, then this is 330 hours per year.

My car does 20,000 per year, at 40 mph ave, therefore 500 hours, and is serviced once a year, generally oil and air filter. Nothing much more. The rest of the car needs a bit more like brake fluid/pads/aircon etc.

Car engines these days are designed to run for 200,000 mile before major rework, and truck engines 500,000.

My boat did 50 hours this year, and will get oil and filters, fuel filters etc and probably fresh coolant. The turbo will get a look at and oil up, and I'll also check the cam drive belt. Therefore I'm hoping for many years of happy and reliable boating...................

Neglect, especially to the heat exchanger is the most likely failure scenario.

I'm always a bit suspect of this argument with marine engines, most planing boats run at cruising revs 10% down on max revs and under continous load, this is like driving your car at 100mph+ up a hill constantly so the 30mph average 10k miles per year is hardly comparable. Unfortunately I fear for a lot of "leisure" market marine engines, a 1000hrs or so is quite a lot and you should buy carefully.

 

[Nick_H]

most planing boats run at cruising revs 10% down on max revs and under continous load

I'm not sure that's the case. Most people have to follow some kind of speed restricted channel to get out of their home port, and most mobo's cover fairly short distances, so the time spent at low revs can be a high proportion of the total running hours.

Suppose I was to go from Lymington to Poole. I start the engines, then they idle for 20 mins until I get out of Lymington channel, then I open up for an hour or so to Poole harbour entrance, then less than 10 knots for another half hour or so, so only roughly half the time is spent at cruising revs. Obviously it varies depending on your home port and where you visit, but most mobos do short hops most of the time. It could be a lot less than half for a mobo going from Swanwick to East Cowes for example. On average, i'd guess a third to a half of the running hours of leisure mobos are not at full cruising speed.

 

[Chris_d]

I'm not sure that's the case. Most people have to follow some kind of speed restricted channel to get out of their home port, and most mobo's cover fairly short distances, so the time spent at low revs can be a high proportion of the total running hours.

Suppose I was to go from Lymington to Poole. I start the engines, then they idle for 20 mins until I get out of Lymington channel, then I open up for an hour or so to Poole harbour entrance, then less than 10 knots for another half hour or so, so only roughly half the time is spent at cruising revs. Obviously it varies depending on your home port and where you visit, but most mobos do short hops most of the time. It could be a lot less than half for a mobo going from Swanwick to East Cowes for example. On average, i'd guess a third to a half of the running hours of leisure mobos are not at full cruising speed.

I wouldn't disagree and its dangerous to generalise, I just think comparisons with car usage hours are completely meaningless. If you take fuel flow through an engine to be an indication of load for comparison, then say a 200hp car at motorway speeds will be using say 2-3gph (30mpg) roughly the same as your 200hp powered boat might use potting out of a harbour to sea, at what is considered light load. However at cruise speed the boat will use say 5-6gph probably more, for the car to use that much fuel it would be doing say 120mph+ or on a race track.

So if there is a comparison to be made between cars and boats I would say that boat usage is equivalent to a track day car, used infrequently, driven gently to a circuit and then thrashed whilst its there. Talking very generaly of course about the average planing mobo and why some seem to need engines changing at low hours.

 

[PCUK]

Can I digress slightly? Flowerpower says that D4 and D6 don't have replaceable liners. Can't they be rebored either?
I'm interested as I am thinking about a boat with a D4 and although I hate Volvo marine for their rip-off ethos I will be even more put off if the engines are literally designed as throw away units!

 

[Thepipdoc]

I wouldn't disagree and its dangerous to generalise, I just think comparisons with car usage hours are completely meaningless. If you take fuel flow through an engine to be an indication of load for comparison, then say a 200hp car at motorway speeds will be using say 2-3gph (30mpg) roughly the same as your 200hp powered boat might use potting out of a harbour to sea, at what is considered light load. However at cruise speed the boat will use say 5-6gph, for the car to use that much fuel it would be doing say 120mph+ or on a race track.

So if there is a comparison to be made between cars and boats I would say that boat usage is equivalent to a track day car (used infrequently) driven to the circuit and trashed whilst its there. Talking very generaly of course about the average planing mobo and why some seem to need engines changing at low hours.

I like this logic and would agree entirely.

 

[MVP]

I think modern engines are quite happy to be used hard - it's lack of use, short runs and poodling around that causes the problems.

MVP

 

[rafiki_]

I agree with MVP. Modern cars/powertrains are designed for a mix of use, and during validation are driven extremely hard. Engine bench tests will do a 400 hour burst test, just below flat out. This is more onerous than flat out, as the fuel system will overfuel flat out, thereby cooling the pistons.

Most marine diesels are derived from truck engines. These are driven pretty hard in order to haul their load. Designed for 500,000 miles at 56 mph = nearly 9000 hours, less the time idling in jams on our roads, or equivelent to getting in and out the marina.

In comparison, most boat engines have an easier life, plus a more consistent coolant temp, as the water varies from about 5 to about 15 C, not -5 to plus 30 ish.

I concur that it is a mix of lack of use and poor maintenance that causes the most problems.

 

[Latestarter1]

Marine engines

There are some simple rules regarding marine diesel engines and long life.

First rule is that reliability and durability should never be confused. In leisure applications it is pretty much impossible to to wear out a diesel engine regardless of colour. We are only really concerned about reliability

Quality of engine installation is a factor often overlooked in perceived reliability. 50% of diesel engine fuel filteration systems I look at are in my book "not fit for purpose". At least 25% of exhaust systems are an accident waiting to happen. Both lead to premuture engine failure. How many boats are propped in such a way that engines fail to meet rated rpm, causing engines to be overloaded, dozens, even brand new ones.

Quality of marinisation components and their ability to remain reliable are variables between different manufacturers, and it is pro-active attention to maintaining sea water pumps and servicing aftercoolers which are key to safe and reliable operation. In the U.S annual aftercooler servicing is pretty much the norm, along with sea water pump overhaul. Many boats in US also have fresh water flushing kits fitted. It is "marine aging" of the bits around the base motor which tend to define the life of an engine.

If a diesel engine IS properly installed the duty cycle is not tough, and there are no shortcomings in the cooling systems of any of the major manufacturers, providing that the engine is nicely loaded up perfectly happy to run at low rpm’s for an extended period without polishing the bores, then pick up the pace and run 2/400 "off the top" for an hour or longer, in fact a diesel engines bread a butter.

On the durability front whilst I note the negative comments regarding Volvo D4/6, parent bore is not the issue, the trend toward lack of service oversize pistons is. However it is my understanding that competitively priced Volvo replacement blocks addresses this.

Before you take out the cudgels on Volvo, consider the Yanmar LYA2 420(440), also parent bore with no repair procedure, try asking Barrus for the price of piston part #719574-22721, I will help you talking £531.00 each plus VAT.

However IF a marine engine is fed a diet of super clean fuel and its cooling system is regularly maintained, as well as the exhaust system being properly designed, boaters can regard expensive horror stories as just that, dock talk.