Diesel Engine Design Life

[lw395]

Extended life is irrelevant in boat engines where the recommended change points are usually 150-200 hours, or typically a season. Conventional oil has no problems with that sort of interval.

Trying to transfer experience for road vehicles is misleading. Boat engines have a specific power output of usually around 30hp/l compared with modern road vehicle engines which are minimum twice that and common now tombe over 100hp/l. A boat engine generates far less heat than a road engine, runs most of its life at 70% maximum - 2200rpm and 20hp for my D1-30 for example. Where is the requirement for lubrication anything like as demanding as that on my 2L turbo diesel Ford (which does require synthetic oil - and gets changed every 300 hours or so) and uses the full revs and power range almost every time I drive it?

Boat engines tend to run a long time at 50 to 70%, as you say.
My car engine never sees over half power for more than a few seconds, or I'd be doing 140mph a lot.....
Not that the wear on valve gear and many of the other dozens of wearing parts is that closely related to power.

 

[dom]

My car engine never sees over half power for more than a few seconds, or I'd be doing 140mph a lot.....

140mph at half power ...Golly!

 

[pvb]

Why do you think you need that and why it is not provided by the oil recommended by Volvo is minimum API CG. Cold weather down to -15 for 15W/40. Given our conditions here, difficult to see what value there is in using a higher specification oil, although Volvo do say it can be used if the lower spec is not available. If it was essential, or even "better" - surely they would recommend only using synthetic or semi synthetic?

The minimum spec demanded by Volvo for bog-standard engines is now VDS2 and CH-4. Back in olden times, the Volvo MD1B was only required to have CD oil, not because it was less demanding, but because that was the best oil grade available at the time. Using better oil in old engines won't harm them.

 

[lw395]

The minimum spec demanded by Volvo for bog-standard engines is now VDS2 and CH-4. Back in olden times, the Volvo MD1B was only required to have CD oil, not because it was less demanding, but because that was the best oil grade available at the time. Using better oil in old engines won't harm them.

For balance, there are odd cases of <=60's engines where synth oil will escape from seals made from cork or leather or some such.

 

[RichardS]

]Extended life is irrelevant in boat engines where the recommended change points are usually 150-200 hours, or typically a season. Conventional oil has no problems with that sort of interval.

Sorry Tranona but you're missing the point. The recommended change point applies to mineral oils. Once you switch to synthetic oil you can safely disregard the recommended oil change intervals.

My Yanmar recommended oil change is annual as I don't do 150 miles per season so 3 - 5 years is easily achieveable with synthetic.

Richard

 

[pvb]

For balance, there are odd cases of <=60's engines where synth oil will escape from seals made from cork or leather or some such.

Yes, the horsehair seals in the old Stuart Turners were susceptible to this, I believe.

 

[RichardS]

On a used low tech boat engine, I think the oil is still just as prone to contamination from water, fuel and combustion by-products, so I think it needs changing roughly as often.

Certainly no harm in changing synthetic oil just as often as mineral oil and gaining from the advantages you list. However, synthetic oil will cope much better over a longer period with the contaminents because of the additional capacity afforded by those same technical advantages. However, if extending the change interval is not something you're comfortable with then you shouldn't do it.

Richard

 

[KellysEye]

>so the basis for your statement is what you were told by Volvo. Hardly an independent source - and he would say that would he not? as the later engines sold as Volvo are not actually made by them.

What I didn't mention is that we we decided to go long distance sailing in 2004 and we checked availabilty of spares and most are in chandlers. Two exceptions are engines and and wind generators. Hence I called Volvo and asked what spares I needed for an MD17C and said what we were doing. He said nothing other other than impellors, fuel and oil filters. That led on to my question of why they are not needed on that engine which led to the life expectency of old and then modern engines. At the time Volvo were making boat engines and his advice was proven right. As said in another post 8,000 hours is the norm for modern engines but doubtless can last longer if properly used and maintained but that means lots of running at high revs.

One other thought is I asked three engine repair shops in St Martin, Guadeloupe and Trinidad which engines the least had to repair. The concensus was Yanmar with no other engines close. Then I asked the same about generators and the concensus was Northern Lights closely followed by Westerbeke.

 

[Tranona]

Sorry Tranona but you're missing the point. The recommended change point applies to mineral oils. Once you switch to synthetic oil you can safely disregard the recommended oil change intervals.

My Yanmar recommended oil change is annual as I don't do 150 miles per season so 3 - 5 years is easily achieveable with synthetic.

Richard

That is not what my Volvo handbook says. It recommends mineral oil but synthetic oils may be used - not the other way round. It does not differentiate in change intervals. Same with all oils.

Why, if your Yanmar recommends a change every year do you go 3-5 years?

 

[Tranona]

>so the basis for your statement is what you were told by Volvo. Hardly an independent source - and he would say that would he not? as the later engines sold as Volvo are not actually made by them.

What I didn't mention is that we we decided to go long distance sailing in 2004 and we checked availabilty of spares and most are in chandlers. Two exceptions are engines and and wind generators. Hence I called Volvo and asked what spares I needed for an MD17C and said what we were doing. He said nothing other other than impellors, fuel and oil filters. That led on to my question of why they are not needed on that engine which led to the life expectency of old and then modern engines. At the time Volvo were making boat engines and his advice was proven right. As said in another post 8,000 hours is the norm for modern engines but doubtless can last longer if properly used and maintained but that means lots of running at high revs.

The advice you received would be exactly the same with modern engines. My Volvo 2030 did over 3000 hours and nothing was changed except oil, filters, drive belt and inmpeller. You will have read in other posts of small Yanmars and Volvos achieving well over 10000 hours.

The life of yacht engines is largely a function of two things, usage pattern and maintenance.

There is nothing extra magic about older engines. They were the best available at the time but no better, and in many ways, inferior to newer designs - which is why they are no longer made.

 

[jerrytug]

..



..older engines. They were the best available at the time but no better, and in many ways, inferior to newer designs - which is why they are no longer made.

In what exact way is my '72 Volvo 'in many ways, inferior to newer designs', can you be specific?
It starts on the button and there isn't much to go wrong.
The chances of an unexpected problem at sea are minute to non-existent.
What do you mean by inferior precisely?
cheers Jerry

 

[RichardS]

That is not what my Volvo handbook says. It recommends mineral oil but synthetic oils may be used - not the other way round. It does not differentiate in change intervals. Same with all oils.

Why, if your Yanmar recommends a change every year do you go 3-5 years?

As fas as I'm aware all yacht auxiliary engine manufacturers recommend mineral oil in the first instance. Many don't even mention synthetic at all but that's simply because they designed and tested their engines with mineral oil. I've never suggested anything else.

The bottom line for both cars and boats is that all manufacturers recommend an annual oil change but why do they do this? Answer: it is simply backside covering / revenue generation on their part, and possibly to ensure that the engine is run up to temperature at least once a year as getting the oil hot is part of the oil change procedure.

Take an extreme case to make the point: an engine does 1 hour running on new mineral oil and is then left used. How long before you need to change the oil? 1 year, 10 years, 50 years, 100 years? Provided that the engine is run once a year to ensure that the bearings retain a molecular coat of oil, you would be totally safe using a double figure oil change period. From that point on in the real world it's simply a matter of comparing hours of use against oil change period to find the sweet spot.

Once you change to synthetic oil the same comparison applies but the change period is pushed further out because synthetic oil is intrinsically better than mineral oil in resisting mechanical and chemical breakdown.

Of course, all this is explicit in industrial diesel engine applications, where I have some experience, where the oil is tested for mechanical and additive breakdown on a regular basis and only changed when the analysis shows that it needs to be changed. Even that is a simplification because with modern synthetic oils it is often the case that the molecular structure of the base oil is sound but the additive package has deteriorated. A new dose of additive is the answer rather than an oil change. Oil changes could be weekly, monthly, annually, bi-annually, whatever. Nobody is looking at the calendar to see if an oil change is due!

As I said above, there is no disadvantage other than the cost in time and money in changing oil in a little used engine on an annual basis as recommended by the manufacturers. However, there is no technical reason to do it so I choose not too.

Richard

 

[lw395]

There is one good reason to change your oil at least annually.
If you ever want to sell your boat, a lot of people are going to ask about such things.
If you narrow the choice of buyers to those that share your exact opinions about extended oil changes, it may be on your hands for a long time.
As you point out, in industrial engines, it is common to monitor by oil analysis. I'm aware of a few people doing this with motorbikes, do you do it with your yacht engine?

 

[charles_reed]

You still see the odd modern car with a pall of smoke behind it, and wonder has it done a trillion miles, has it been abused, or is it just chance that things fail?

Driver just put his foot down rather fast.
Diesels have an unvaried air supply, acceleration is by introducing more oil into the engine-cylinders, hence the smoke.

 

[Retired in Crete]

There is nothing extra magic about older engines. They were the best available at the time but no better, and in many ways, inferior to newer designs - which is why they are no longer made.

You forget than many "improvements" are made to reduce manufacturing costs and have nothing to do with better life or performance.

John

 

[Trundlebug]

As fas as I'm aware all yacht auxiliary engine manufacturers recommend mineral oil in the first instance. Many don't even mention synthetic at all but that's simply because they designed and tested their engines with mineral oil. I've never suggested anything else.

The bottom line for both cars and boats is that all manufacturers recommend an annual oil change but why do they do this? Answer: it is simply backside covering / revenue generation on their part, and possibly to ensure that the engine is run up to temperature at least once a year as getting the oil hot is part of the oil change procedure.

Take an extreme case to make the point: an engine does 1 hour running on new mineral oil and is then left used. How long before you need to change the oil? 1 year, 10 years, 50 years, 100 years? Provided that the engine is run once a year to ensure that the bearings retain a molecular coat of oil, you would be totally safe using a double figure oil change period. From that point on in the real world it's simply a matter of comparing hours of use against oil change period to find the sweet spot.

Once you change to synthetic oil the same comparison applies but the change period is pushed further out because synthetic oil is intrinsically better than mineral oil in resisting mechanical and chemical breakdown.

Of course, all this is explicit in industrial diesel engine applications, where I have some experience, where the oil is tested for mechanical and additive breakdown on a regular basis and only changed when the analysis shows that it needs to be changed. Even that is a simplification because with modern synthetic oils it is often the case that the molecular structure of the base oil is sound but the additive package has deteriorated. A new dose of additive is the answer rather than an oil change. Oil changes could be weekly, monthly, annually, bi-annually, whatever. Nobody is looking at the calendar to see if an oil change is due!

As I said above, there is no disadvantage other than the cost in time and money in changing oil in a little used engine on an annual basis as recommended by the manufacturers. However, there is no technical reason to do it so I choose not too.

Richard

You appear to be missing one important point: the usage pattern and environment of marine engines.
One of the main reasons why engine manufacturers recommend an annual oil change is because over the winter the engine sits unused for up to 6 months in a damp, salty and cold environment.
As the oil gets contaminated during diesel engine use by acidic and abrasive particles, the additives break down as you correctly state. Engine manufacturers therefore recommend an annual oil change, which should be done (although I'm not sure they state this) at the end of the season so it sits with fresh oil over the winter and gets maximum protection. It isn't "backside covering" there is genuine reasoning behind it.

Other engine types don't have this usage pattern, they're used far more regularly so the number of usage hours between oil intervals becomes far more relevant and more important, hence the use of semi and fully synthetic oils.

Switching to semi or fully synthetic oil in a marine engine doesn't give you any benefits in this respect (extended service intervals): they recommend annual oil changes exactly because of the above reason, so you don't get contaminated oil sitting next to the bearing surfaces for several months in the cold and damp.
You simply don't get any benefit from using oil that can (in other applications) last for longer (i.e. more running hours) between changes - running hours aren't the determining factor in a marine engine.

 

[geem]

You appear to be missing one important point: the usage pattern and environment of marine engines.
One of the main reasons why engine manufacturers recommend an annual oil change is because over the winter the engine sits unused for up to 6 months in a damp, salty and cold environment.
As the oil gets contaminated during diesel engine use by acidic and abrasive particles, the additives break down as you correctly state. Engine manufacturers therefore recommend an annual oil change, which should be done (although I'm not sure they state this) at the end of the season so it sits with fresh oil over the winter and gets maximum protection. It isn't "backside covering" there is genuine reasoning behind it.

Other engine types don't have this usage pattern, they're used far more regularly so the number of usage hours between oil intervals becomes far more relevant and more important, hence the use of semi and fully synthetic oils.

Switching to semi or fully synthetic oil in a marine engine doesn't give you any benefits in this respect (extended service intervals): they recommend annual oil changes exactly because of the above reason, so you don't get contaminated oil sitting next to the bearing surfaces for several months in the cold and damp.
You simply don't get any benefit from using oil that can (in other applications) last for longer (i.e. more running hours) between changes - running hours aren't the determining factor in a marine engine.

This cant be correct. What about all the marine engines in fishing boats that log 5000 hours per year. Clearly these are the same engines. My own Perkins engine says change oil every 500 hours or annually. Clearly you would be changing the oil ten times per season when fitted to a fishing boat.

 

[Trundlebug]

This cant be correct. What about all the marine engines in fishing boats that log 5000 hours per year. Clearly these are the same engines. My own Perkins engine says change oil every 500 hours or annually. Clearly you would be changing the oil ten times per season when fitted to a fishing boat.

The important point of note being "or annually"
I agree in a fishing boat doing lots of hours there is a clear case for the use of semi or fully synthetic - but also remember those boats are used all year round.
But we were discussing leisure boats, and leisure engines whose usage is far from the same.

My VP MD31A's interval for example is only 100 hours or annually. Simply no point whatsoever using anything other than mineral oil with that sort of interval or leisure use pattern.

 

[dominick21]

Most of the machines are ruined out by improper usage and maintainance.

 

[lw395]

T....

My VP MD31A's interval for example is only 100 hours or annually. Simply no point whatsoever using anything other than mineral oil with that sort of interval or leisure use pattern.

Is that one of the engines for which Volvo say using their API CI-4 oil allows increased drain intervals?
A new oil pump retails at about 1000 euro. Possibly a case for being choosy about what goes through it?