Diesel Engine Oil Change Frequency?

[DumnMad]

Originally Posted by a64pilot

.......
However for the average lowish RPM, normally aspirated Marine Diesel, it’s unlikely you will ever break down the oil. For example my old 4JHE at 40HP is I believe the same displacement as the 100 HP turbo is. Which one do you think stresses the oil the most?
Anyway those type of motors need the oil changed due to the oil being laden with soot, soot is carbon, and carbon is very abrasive.
.....

Thanks.
For those of us with low revving naturally aspirated engines using mono oils, would you give a brief on what sort of usage is bad for getting soot into the oil.
Also, any comment on acids in the oil?

[captainstubbie]

Again my 2 cents, once a season is satisfactory.

[Exile]

I've always done 100 hours or 1x/year, and prior to any extended lay-ups. This usually translates to 1x/year for both engine & genset. 500 hours for valve adjustments on both engines or any indication of hard starting. This is almost as easy on my boat as oil changes. I'll change out primary & secondary fuel filters 1x/year for both engines as well, even if I haven't consumed many hours. Not sure how necessary this really is so long as the vacuum gauges show them to be unobstructed. Otherwise it's 200 hours for fuel filters, or sometimes before a lengthy passage.

[a64pilot]

Originally Posted by DumnMad

Thanks.

For those of us with low revving naturally aspirated engines using mono oils, would you give a brief on what sort of usage is bad for getting soot into the oil.

Also, any comment on acids in the oil?

Any engine has blow by, that is of course combustion gasses that blowy by the piston rings and valve seats, mostly piston rings.
This blow by is what contaminates oil with soot. Just operating the engine in any manner will soot the oil up.
Contrary to many people’s belief, and oil that turns black fast is a good oil, and oil that stays looking clean is not. The oil that goes black fast is doing its job and putting the soot into suspension, it has a good detergent additive package.

Acid of course comes from the combustion of fuel that creates water and I guess CO2 that combines into acid? Honestly unsure of exactly where the acid comes from but it is a normal by product of burning fuel.
In aircraft at least it is desired to run your oil temp at 180F or higher to burn off the moisture that forms acid. So not letting an engine get to full operating temp will cause acid to form faster.
One of the few things I believe oil analysis is good for is determining acid build up. Oil has what is called TBN or total base numbers, that is its ability to neutralize acid, the oil losing its ability when the TBN is low, and oil analysis can tell you the TBN. Combine that with hours and time of operation and you can tell how much life the oil has left in it.

[DumnMad]

Thanks a64.
Sort of confirms that trucking chart showing engines with high mileage long steady runs are happy with 400hours between oil changes while mileage made up from short trips and more throttle should be much more frequent.
A massive difference in oil change frequency required for day sailors vs long distance motor-sailor cruising.

[a64pilot]

The other thing about OTR trucks is I believe their oil capacity is measured in gallons, and their engines are designed for much longer times between overhauls. I don’t think million mile truck motors are all that uncommon, and that industry a reputation for an extremely long life, sells.
It’s not really that hard to design a small boat engine to last at least twice as long as they currently do, but it would be bigger, heavier and much more expensive, and that new boat owner that will keep it five years and maybe average 200 hours a year won’t pay for that, doesn’t want it.

[Alberg30Shill]

Originally Posted by TJ D

I really don't think you're wasting oil. The stuff gets recycled, anyway. The cost of oil is pretty tiny in the grand scheme of things, too.

The change should be done at the end of the season, running the engine briefly after it's done to distribute clean oil onto all of the engine's surfaces, as was laid out a couple of posts ago. He's spot on in his analysis, I think.

Umm, 'recycling' used oil is nearly always burning it in furnaces.

[Lepke]

One of the big problems with not changing oil in a diesel is the soot builds up. The more soot in the oil, the more buildups in the engine, restricting or blocking small oil passages. Reducing oil flow to a turbo or the rockers usually results in failure. I've seen heads that were not repairable. In over the road trucking, it's a big problem for individuals or small companies buying used trucks. Some of the big companies doing high mileage, buy new trucks often and sell their old but new looking trucks in large lots at about 500,000 miles with only a couple oil changes. They change oil just before selling, but under the covers are buildup and damage. It's common for well maintained trucks to do over a million miles between overhauls.

[CarlF]

The manual for my Yanmar 4JH4 HTE 110hp diesel calls for oil change every 250 hours or 1 year.

Same manual calls for replacing EVERY rubber water and fuel hose every two years.

Not sure where that leaves you

[Simi 60]

100 hours and 3 litres on the genset - oil is black
250 hours and 37 litres on the big motor - oil looks clean
Both using Castrol RX 15w40

[daletournier]

I'm a (ex) mechanic and do not claim to no anything about oil, sure I know what I've been taught but I've also seen examples that have me questioning what I apparently know.

Eg. My apprenticeship was building automatic transmissions. We used to sell 20,000km services, which were basically oil changes. The foreman was the most knowledgeable bloke on the block, but his Xb falcon had 180,000km on the borg warner auto without ever changing the oil, we were regularly rebuilding these autos at that milage.

80% load 80%of the time, diesel mantra. I've said this to many people, yet my mates yanmar that he runs morning and night under virtually no load charging batteries, and never works the engine hard now has just under 15,000hrs on it! Starts the moment you touch the button.

Met a guy on 60ft trawler in the Philippines, large engines, and immaculate huge walk in engine room etc, and he doesn't believe engine oil needs to EVER be replaced, but he runs large filters and changes them regularly, I can't remember the details, but I do remember him being no fool his boat was amazing and he spoke as if educated about the topic.

My point is I DON'T KNOW, I know what I read but I've seen some examples that make me question what we know? I suppose this applies to many subjects.

I change every 100-150hrs, I'm to well trained... Lol.

[daletournier]

Oh one more thing, I A64 mentioned black oil means good oil as it's absorbing what it's meant to, I understand BUT here's the thing, I my last yanmars oil was always black regardless of the oil I used, but I and due to my travelling I had to buy what was available.
The new (12months now) has spotlessly clean oil, I purchased her in Australia thus able to get very good oil and have changed it twice.... A64 is more knowledgeable than I, but I I have no doubt BUT once again I'm that sure about what we know. Devils advocate.

[daletournier]

Originally Posted by daletournier

Oh one more thing, I A64 mentioned black oil means good oil as it's absorbing what it's meant to, I understand BUT here's the thing, I my last yanmars oil was always black regardless of the oil I used, but I and due to my travelling I had to buy what was available.
The new (12months now) has spotlessly clean oil, I purchased her in Australia thus able to get very good oil and have changed it twice.... A64 is more knowledgeable than I, but I I have no doubt BUT once again I'm that sure about what we know. Devils advocate.

Sorry about typos, crazy phone thinks it's smarter than me.

[Exile]

Originally Posted by daletournier

Oh one more thing, I A64 mentioned black oil means good oil as it's absorbing what it's meant to, I understand BUT here's the thing, I my last yanmars oil was always black regardless of the oil I used, but I and due to my travelling I had to buy what was available.
The new (12months now) has spotlessly clean oil, I purchased her in Australia thus able to get very good oil and have changed it twice.... A64 is more knowledgeable than I, but I I have no doubt BUT once again I'm that sure about what we know. Devils advocate.

I always assumed the black oil was related to the age of the diesel engine, and attributable to more blow-by as rings, valves, cylinder walls, etc. slowly deteriorate. My genset & truck engine are both quite old and the oil turns black almost as soon as I change it. But my propulsion engine is newly rebuilt and with only 400 hours the oil still stays clean looking. Doesn't seem to make any difference performance-wise, although the two older diesels do use some oil now whereas the new one doesn't. Not sure the color/appearance alone is either here nor there w/o further analysis.

[Cadence]

Originally Posted by Alberg30Shill

Umm, 'recycling' used oil is nearly always burning it in furnaces.

I recall using recycled oil as a college kid with a junker and the proverbial lack of a pot to piss in. When you burn more oil than fuel it makes sense.