Intervals between oil/filter changes

[Ric]

I have a Volvo diesel engine on my boat which requires oil changes every 100 hours. My car also has a diesel engine, and the intervals are every 25000km, which is approximately every 500hours given the slow speeds of modern traffic.

Why the huge difference?

Bear in mind that my car engine has specific power about eight times that of my boat engine, it is turbocharged and has a far higher compression ratio, the rpm goes as high as 6000rpm, rpm fluctuates wildly, and the engine operates over a much higher temperature range.

The oil in my boat engine on the other hand has a really easy life - no turbocharging and a low compression ratio, relatively low and steady rpm, nice steady operating temperature.

On the face of it, one would expect much longer intervals between oil changes on a boat engine than on a car engine.

I was at Cannes boat show today, so asked the Volvo/Nanni/Yanmar technicians this exact question. They all gave me different and equally unconvincing answers.

Can anybody here do any better?

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[snowleopard]

the main reason for changing boat engine oil is that the combustion products create acid in the oil which attacks the innards over time, especially in conjunction with condensation.

the most important thing is to change oil before the layup. also wise to change the filter- mine rusted through over the winter!

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[BarryH]

Also look at the difference in quality of the fuels. Road fuel is of a higher quality that has to meet specific standards. Whereas marine fuels do vary in quality between outlets as I have found.

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[jimi]

Your car would probably benefit from more frequent oil changes. The following precis from a Volvo car forum summarises my thoughts and is what I've been led to beleive. I actually change my car oil at half the recommended interval.

Engine temperatures over a period of more than 50 hours changes the characteristics of the oil, produces gummy and / or carbon deposits on all manner of internal engine surfaces and will in time block or partially block small orifices and /or clearances around bearings. Some of the carbon material produced, along with the dirt which is collected makes a really great abrasive for all moving engine parts. The more abrasion that goes on the more abrasive is produced and so on. That is why a clean oil filter is so important. Synthetic oils are more resistant to high temperature transformation than natural hydro carbon oil and they have lower coefficient of friction for equivalent grades. However most of the junk that collects in mineral oil will also collect in synthetic oil. Therefore, use synthetic oil if you like, but change it just as often.


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[BarryH]

Good grief! Your more of an anorak than me, so <A target="_blank" HREF=http://minimopar.knizefamily.net/oilfilterstudy.html>this</A> will probably interest you. Goes into some depth if you look around the site.

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[FullCircle]

Please bear in mind the design generation of both engines.
I had an old Morris Minor which required the king pins to be greased every 250 miles.
An oil change on my 3 litre V6 Ford engine (designed in the sixties) was recommended for 3000 miles. One of the reasons for this was build tolerances. Remember that you had to run in engines then. Not really so anymore. In fact todays engines gain horsepower over the first 10000 miles or so. It has been known for a modern 2 litre diesel to 'gain' 10 Bhp.
The fuels used then (and like marine diesel) had a relatively unsophisticated chemical additive base.
Also note the recommended grades of oil. Gone are the days of using straight 30 grade, or 20/50. Modern designs are using synthetic oils of 5w/30 or similar because they have better molecular control in the tighter tolerances, and better flow characteristics.
Manufacturers go to great lengths and thousands of hours/miles testing to establish the service intervals, and the industry standard is a design condition of 15 years/150000 miles, and they will warranty the product up to 5 years (some standard, some boaught as extension). They abhor paying out warranty, and fear the reputation that comes from a quality standpoint if engines have a habit of going bang when used by the public.
In the case of marine diesels, most have their roots in the past. As you say, they have a low specific output for capacity, and have greater build tolerances. The build tolerances mean that movement in the engine is not as controlled as it should be, leading to wear. These tolerances are partly taken up by oil thickness. The oil gets contaminated from combustion blow by in cylinders and heads, and fuel being relatively untreated has a high carbon deposit habit.

I always have high mileage vehicles, and still adhere to the manufacturers specification for oil/filter changes. My last BMW had 200000 miles, and is still going strong, An Audi I sold 10 years ago to a mate in France now has over 300000 miles on the original engine. My current Jaguar XJ6 (slightly old technology!!) has 150000 miles and does not burn from Max to Min over 10000 mile intervals.
By the way - I experimented with my Reliant Scimitar, and went to synthetic oil at 60000 miles, and DOUBLED the oil service interval to 6000 miles from 3000. I finally rebuilt that engine with over 200000 miles on it. It only needed rings, and valves/guides.


Doesn't answer your question really, but I hope it sets you thinking.


Jim


<hr width=100% size=1>Our engine will never wear out - it only runs for 5 mins before packing it in again.

 

[robind]

"Use a good oil and keep it Clean" I agree with acids comment etc! dont leave the seasons oil to fester in the layup period. Buy a cheap Oil "Pump-out" pump, and even if you dont change the filter/s change the oil (ie dilute the remaining oil in the filter) and run your engine regularily under load during the season and out if possible.
Rob

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[Ric]

Interesting that there were also lots of totally differnt answers on here from those given to me by the Yanmar/Nanni/Volvo technicians. Incidentally, their answers were:

Volvo - "it is because of the salt in the air". I asked why they did not suggest longer intervals on boats sailed on freshwater - but they had no answer.

Nanni - "boat engines never get properly warmed up".

Yanmar - "car engines have an easier life than boat engines - they rev higher and are not left running at constant rpm".


Maybe it is a combination of all of these reasons. But I suspect it is just because there is very litte R&D in boat engines and that they are built to lower manufacturing tolerances, and there is little investment in them. After all, there is one Chrysler car engine that goes 100,000 miles between oil changes which equates to around 3000hours of use.

My theory was sort of borne out by the other question I put to the engine technicians - namely why they all install automobile derived alternators to their sailing boat engines, even when it is clear that the standard regulators are hopeless for the needs of a sailing boat. It would cost the manufacturers just a few euros to install a smart-regulated alternator - certainly a lot less than after-market installation of the likes of Advercs. None of the technicians had really convincing answers to that, except Yanmar who do offer a smart alternator as an option.

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[boatone]

IMHO most problems with alternator output levels are usually caused by inadequate cabling and unneccessary use of blocking diodes. Also, in may cases peeps try to get away with underweight batteries. Put a DVM across the positive output from the alternator and the positive of the battery and measure the voltage drop......if its more than around 0.2 of a volt do something about it !

<hr width=100% size=1><A target="_blank" HREF=http://www.boatsontheweb.com/> Website, Photo Gallery, Chat Room, Burgees</A>

 

[duncan]

hmmm...
I have a 3.0l 4 cylinder turbo diesel in the Landcruiser producing around 120 hp and a 3.54l 4 cylinder turbo diesel in the boat producing 240 hp
the boat engine tends to be using all it's hp at any given revs as drag is constant whilst the car gets a pretty easy ride on motorway journeys in contrast (up to about 70mph drag isn't that great).
I change the boat oil and filter 2wice a year - at an hour and 35 quid for parts it doesnn't seem too great a burden; and it even gets GTD.

I don't think tollerances etc are that different for many turbo engines - however I believe the lack of 'constant use' means keeping the oil clean (acids etc as already mentioned) is the important issue.

<hr width=100% size=1>madesco madidum ..../forums/images/icons/smile.gif

 

[sailorman]

HOW DO U FIND TIME TO SAIL ???????

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[FullCircle]

<HOW DO U FIND TIME TO SAIL ??????? >

Set the boat off on Autopilot Friday, and collect it again Sunday evening.
I have driven between 50-75k miles a year for over 20 years. I also have to pay for them myself, so I like them to last.

Jim

<hr width=100% size=1>Our engine will never wear out - it only runs for 5 mins before packing it in again.

 

[dickh]

Interesting that the manufacturers cannot give a constant answer. I would argue that as marine diesels are marinised industrial engines from the likes of Kubota, Perkins, Mitsubishi etc. they are built to the same standards as automotive engines. Industrial engines certainly run for thousands of hours between overhauls and generator engines run at constant speed, and will run at that speed from start-up.
From my experience with industrial engines, there is a lot of R&D goes into them, but with reliabilty being a criteria, they don't go for hi-tech state of the art solutions like electronic control, supercharger, intercoolers, turbo chargers etc etc. This sort of kit needs to be able to be serviced in out of the way places with no access to modern workshops.
There is an interesting US site from a guy called Pascoe who is a marine surveyor and his opinion is interesting although very US and petrol biased - he apparently knows little about European/Japanese small diesels and all his experience is with big US diesel & petrol engines.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif