Diesel Engine Oil Change Frequency?

[Kenomac]

Originally Posted by rwidman

You don't have to cop an attitude about it!

If you are the "service tech" why are you asking random strangers on the Internet such basic questions as "when should I change my oil?"

No attitude intended. Don't be deceived by my internet appearance, I'm actually very friendly.

[P3sailor]

Don't believe there is any good answer for this question because of the quality of the oils available. That said, I would go with an annual oil and filter change and if one wants to have an oil analysis done each time. A good facility would be able to tell you if your engine is making metal and pretty much pinpoint the problem areas by breaking down the quantity and type of metal the analysis revealed.
As far as when to change the oil (beginning or after the season) I prefer the beginning, only because now, the oil fresh oil has not been sitting in the crankcase and/or oil pan for six months and, if done at the end of the season, after the oil change most individuals run the engine for a short period of time to check for leaks, etc. Generally, the engine is not run for a long enough period to rid the system of any moisture so, now, that moisture is sitting in your engine and possibly causing unwanted corrosion on whatever surfaces it is in contact with. Seen and heard of many oil pans rusting through, in automobiles, mainly because of moisture being present. This is something everyone has an opinion on, do what you feel is right or what has been working for you.

[mickeyelam]

If you change the oil once per annum, definitely do it before putting the boat away for the season, not at the beginning of the season. No matter how good the condition of your engine, there will be combustion product blow-by getting into the crankcase past the piston rings and thus into the oil. Those blow-by products can (will) form acidic compounds in the oil, even if ultra-low sulfur diesel is used. Such acidic compounds are not good for bearing journals and other machined surfaces.

Basically, on a once per annum schedule, change the oil immediately before the longest period of non-use for the engine, run the engine BRIEFLY to distribute the fresh oil throughout the oil galleries and into all bearing journals, etc., and shut it down. This provides the cleanest environment for your engine's internals and should contribute to long life for that expensive asset.

We've all heard the stories of owners never (or very infrequently) changing the oil in an engine and the engine continuing to run trouble-free for years or decades. I'm sure these instances do happen, but I view them as the equivalent of a smoker that continues to smoke for years or decades and never gets lung or heart disease or any of the other ailments that come along with cigarette smoking in most people. While these types of results do happen, it's important to keep in mind that they are not typical; certainly, they are not typical enough to warrant the gamble on them occurring for me in my mind.

Finally, I do not believe the savings of natural motor oil over synthetic oil is enough to warrant not using synthetic oil. If we're talking one change per year, then you're probably looking at a cost delta between natural & synthetic oil of less than $30US on an annual basis. For such complex, mission-critical pieces of equipment such as engines (of any type) providing the BEST maintenance materials such as engine oils, belts, filters, etc., is cheap insurance to help promote reliability and longevity.

[TJ D]

I think that it's pretty cheap insurance to do an oil change prior to laying up. That seems to be sort of accepted as 'best practice' in the workboat world, anyway.

Change intervals are determined for the most part by the oil capacity of the engine. The boat I'm running around on right now takes 260 gallons of oil in each main, and our change interval is 1000 hours. That's right, 520 gallons to do a service!

As was mentioned before, used oil takes on different chemical properties, and it can slowly attack the inside of the engine. This may or may not really have any harmful effect in the real world.

For my part, if I'm leaving the boat for more than a few months, I do change the oil, but I'll often leave the old filter in place for the next season. It's quick and pretty cheap that way.

Just one guy's view...

[Kenomac]

Excellent point! Maybe we should also be discussing whether to do the oil change at the beginning of the season or at the end. Also, what does everyone think of the new (or rather not-so-new) synthetic multi-fuel oils.

Another point: Nearly everyone (myself included) recommends changing engine oil every year, but very few people actually do it like me. So this discussion is really about... should I change my habit? Am I wasting oil?

[mickeyelam]

Originally Posted by P3sailor

Seen and heard of many oil pans rusting through, in automobiles, mainly because of moisture being present.

I have to believe that any rusting through of oil pans is due to external water/road salt impingement coupled with infrequent removal of such road salt rather than it being caused by moisture internal to the oil pan. Just looking at the chemistry and mechanics of this idea, if you have enough water in your oil pan to promote corrosion perforation, you have larger problems than such oil pan corrosion!


If you're talking about possible corrosion pitting of the interior of the oil pan, then I suppose that COULD be possible in SOME situation, but if it happens, your oil is doing an unthinkably poor job of coating the interior of your engine. Keep in mind that for normal (iron oxide formation) corrosion of iron/steel alloys to occur beyond a surface coating of rust, you need both a source of oxygen to allow the rust formation as well as a method of for the oxygen to penetrate the rust layer; such a method usually involves something like the scrubbing action of road grime/salt/water impacting the surface of the vehicle. If bulk water were present within the oil pan, a surface layer of rust might form, although I'd expect the oil coating to prevent that.

At any rate, good oil change practice still indicates changing the oil BEFORE a period of non-use so that you remove any of the moisture that may have accumulated within the engine as well as removing the combustion by-products that form corrosive/acidic compounds. Leaving those combustion by-products in the engine over a period of non-use is a recipe for internal corrosion, as such compounds have an opportunity to accumulate/pool and cause corrosion during the period in which the engine is idle.

Think of it this way; your engine oil, after 100 hours of use since the last oil change, is a soup of various compounds. The most common compound in that soup is still oil, but there are a number of acidic compounds that were formed by the combustion product blow-by, as well as particulates that can harden during a period of non-use. You tell me, would you pour battery acid into your crankcase and let it sit for several months?!?!

[MarkSF]

I don't know what you mean by new multi-fuel oils. Oils have been selling with a C (compression) and S (spark) API rating for decades.

Synthetic has been around for decades too.

[TJ D]

Originally Posted by Kenomac

Excellent point! Maybe we should also be discussing whether to do the oil change at the beginning of the season or at the end. Also, what does everyone think of the new (or rather not-so-new) synthetic multi-fuel oils.

Another point: Nearly everyone (myself included) recommends changing engine oil every year, but very few people actually do it like me. So this discussion is really about... should I change my habit? Am I wasting oil?

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.

[Cadence]

Originally Posted by MarkSF

The manual for my Universal 5424 is now 33 years old. In that time, diesel fuel has gone from high sulphur to ultra-low sulphur, and engine oil from straight grade dino oil to multigrade with new options like synthetic, and semi-synthetic.

It's entirely appropriate to discuss this issue.

With a modern synthetic oil, I wouldn't worry too much about stretching out the engine hours a little, after all, most cars (including diesels) now run 10,000 mile intervals, which is equal to about 200 hours. However, they also require at least yearly changes.

My Universal gets oil changes every year, and it's done maybe 75 hours in that time, so I just use ordinary Shell Rotella T. If I were doing more than 100 hours in a year, but less than 200, I would switch to synthetic, and keep the yearly interval.

That's what I would do. YMMV.

BTW, I think the determination for diesel oil change intervals is mainly contamination. A diesel puts a lot of dirt into the oil, and the oil has a limited capacity to suspend it. Just try wiping the dipstick on a tissue, and you'll see what I mean. That's why I want to change the oil at least yearly, to flush out the suspended fine particulates.

Engines that have had regular oil changes look better inside. Clean surfaces in the heads, vs. dark or black deposits.

On the Rotella T. I wouldn't use anything else in diesel or gas.

[Bleemus]

I change my oil every 125 hours and at the end of the season.

[Fence Man]

I'm religious about oil changes on the boats. I guess it's a bit of paranoia because of the high moisture environment, and not wanting my off time ruined by breakdowns. On the flip side, we run equipment as high as 500 hours between oil changes. One piece of equipment has a 100 HP Yanmar, and runs at half throttle all day every day. I like to get them changed at the 250-300 hour mark, but it never happens. We have some 10,000+ hour engines that don't show any sign of petering out. I do, however, start my days by going through a couple tubes of grease and checking fluid levels. I suppose the big difference in the two situations would be the relatively short amount of time we put the hours on equipment vs the year it takes to put 100 hours on a boat engine.
I'm with Ken on the end of season/beginning of season bit......Seems there would have to be some advantages to both??? Excess moisture/condensation over the off season?

[redbeard1]

Hi,

We change every 75-100 hours and the last day of the season.

Most of what I have read with regard to when and why is consistent. 1) It's the anti-corrosion additives that break down first not the lubrication properties 2) The engine should operate hot enough to evaporate any moisture inside the engine. Using the engine to just get out of harbor and back (our typical use pattern) is bad and means you should change oil sooner than normal. 3) Change oil just before winter storage. Ideally the anti-corrosion additives should be as fresh as possible for the 6-8 months of storage.

Good luck

[Sailmonkey]

I change our oil every 250 hours or annually...whatever comes first (usually annually). If I was going to put the boat to bed for the winter I’d change the oil prior to layup and run the engine long enough to circulate it. The idea being that the new oil will flush the acidic oil out of the passages for the long storage.

[Scaramanga F25]

100 hours on engine, 150 hrs on gen.

[Pyxis156]

Originally Posted by Kenomac

Excellent point! Maybe we should also be discussing whether to do the oil change at the beginning of the season or at the end. Also, what does everyone think of the new (or rather not-so-new) synthetic multi-fuel oils.

Another point: Nearly everyone (myself included) recommends changing engine oil every year, but very few people actually do it like me. So this discussion is really about... should I change my habit? Am I wasting oil?

Hi Ken,

I believe I have the same 100HP turbocharged engine as you (Yanmar 4JH4-HTE?) and had many of the same questions. For the past three years I have run a synthetic Delo "diesel only" engine oil and for the past two have been performing engine oil analyses. This year I switched to a synthetic multi-fuel oil and am running engine oil analyses every six months (as opposed to annually at oil change) as part of my experiment since I don't want to completely hose my engine if the new oil isn't working out. Happy to report that so far so good with the first oil test at 75 hours indicating the multi-fuel oil is able to handle the contaminant loading a diesel puts on the oil as well as the synthetic Delo "diesel only" oil I was running. And I am very pleased with the performance of the new oil as the engine runs slightly cooler at high RPM's which is indicative of improved overall cooling and friction reduction. I will be completely sold if everything checks out OK when I run my second oil analysis at the one year point.

Regarding oil change intervals, I believe that extended intervals are not a good thing for diesel engines regardless of the claims of the oil. My past oil analyses indicate that, at least on my engine, the TBN additives that combat acids (that are more of an issue with diesels) get used up fast enough that an extended oil change interval would be problematic. Plus, diesels "load" the oil with contaminants more than gasoline engines do, and extended oil change intervals only exacerbate that problem. So to answer your question, I definitely don't think you are wasting oil by changing it each season.

As to when to change the oil, I would think doing it at the end of the season makes the most sense. Your used oil at the end of the season has acids, contaminants both from the combustion process and normal engine wear, and possibly even some moisture in it due to the light loads it sounds like you impose on your engine. Letting all that sit in the engine over a few months with no flow at all would just encourage sludge formation in the oil pan and other places the oil pools, and the acids and possible moisture won't be doing the engine any favors if left in there. Changing it at the end of the season gets rid of all that and gives your engine clean oil to sit in.

And as you pointed out, the Yanmar manual indicates an oil change every 150 hours OR 1 year, whichever comes first. I believe this is due to letting the engine sit for extended periods in used oil, even "lightly used" oil, is not ideal. If I ran my engine five hours in the previous year would I change it? Probably not, it is still essentially new. But at some point it isn't new anymore even if "lightly used", and I think that is the point of the 150 hours or 1 year criteria... even slightly bad oil is still bad if left in an engine for an extended period of time. You are going to change it one way or another, and there seem to be real benefits and no real downsides to doing it before you let the engine sit for a period of time, so my vote goes for doing it at the end of the season.

Hope this helps...