Oil change

I have a Cummins QSB 5.9. Last season I only put 125 hours on fresh oil & filter change. The manual specifies oil change interval as annual or 250 hours. I've always believed that the annual interval was based on "frequent shorter runs" where oil may not reach high enough temperature to evaporate moisture. In my case, I've always run engine long enough to avoid moisture contamination.

My question is: does engine oil really degrade when engine is not operated for extended period? I realize that 4 gallons of Delo 400 15w-40 is not a major expense in the scheme of things, but I also want to avoid unnecessary waste. I'm thinking of operating another 100 to 125 hours in the next 5 months and changing the oil at the end of the season. What do others advise?

Issue is zincs more than oil or coolant. Some engines like the Cummins QSC need to have the after cooler and fuel/oil cooler anodes replaced every three months regardless of engine hours. We’re at around 200hrs. At that point so just do the whole damn thing. The fuel filter is big bucks but the rest reasonable. While we’re at it replace the impeller every six or 9 months. Also a chunk of money. Use T4 but given these intervals may back down to something cheaper that Cummins says is OK. If we winter haul regardless of hours do a oil change. Maybe not the filters depending upon hours. Depending upon g how long we’re going to be out of the water take out impellers so they don’t get a set.
What you’re worrying about is acid and other contaminates in the oil not the oil breaking down. So you need to think about how much damage will be done with no hours and just sitting which depends upon how long it sits. That why I like an oil change immediately before going on the hard.

Most qualified recommendations are to change the oil no less than annually. We put new oil and filters in all the powerplants every fall, regardless of hours. I will be doing mid-season oil changes this year since we will be running lots of miles and hours.

For us, the zincs are on their own schedule. Impellers get replaced every spring on the gens and every other spring on our wing engine. Our main is keel cooled so no zincs.

Bottom line is, as you mentioned, oil is cheap and not worth running old oil that may/does contain contaminants from use that lessens its ability to protect your expensive engines. I think annual oil changes are necessary regardless of minimal hours and fully heating the engine at each run.

I change my oil at least annually just because it's a prevailing recommendation, and it's cheap and easy to do.

However, I have seen nothing to suggest that oil goes bad with age. There are no expiration dates on oil, but I suppose the additives could settle out if they are in suspension. But even then, they would mix quickly. It's been a while since I've had an oil analysis done but I don't think they adjust for pure age of oil vs engine hours.

Would be interesting to see an oil analysis on 100 engine hours at 6-mos vs 3-years.

Peter

Have the oil tested and let the report tell you if it needs to be changed. Oil and engines have come a long way since the replace annually opinions were valid. I use Blackstone.

I change oil filters every 250 hours. I change oil every 125 hours or annually. My engines only spec oil changes every 250 hrs.

I didn’t use synthetic oil so that should say I should change more often.

I also adhere to changing more often because it’s a known standard for maximum engine life. Nobody can argue that dirty contaminated oil is as good as clean new oil.

I changed twice a year and did some cruising in winter. Kept the engine compartment well above 40 degrees. That probably reduced condensation.

If you do abnormally high hours like going to Alaska and back most of the time I did an additional change mid summer at a stop where you stay a few days.

I always had enough new oil for more than one oil change. Stuff happends.

These " discussions" are always interesting... especially when there is little data or analysis results included.
I always see the argument that oil is cheap and cleaner oil HAS to be better than dirty.
News flash it is hard to tell the difference visually between oil at 25 hrs, 50 hrs, 100 hrs vs 150 hrs.
If you subscribe to the oil is cheap insurance and 100 hrs is better than 200 hrs...
How can you argue with the sentiment that 50 hr change "better" for your engine than 100 hrs?
Where does it stop getting better? 25 hr oil is notably black in diesels so changing then better than waiting to 50 hrs!

Synthetic... why? Contaminants aren't less in synthetic?

Why are boats that much different than OTR trucks where best practice is to manage oil changes based on analysis?
Why don't you hear the argument that "analysis is cheap insurance" as often as the "oil is cheap insurance"
Are owners doing analysis and ignoring the results & recommendations or is it they distrust the (scientific) analysis results & recommendations and therefore don't subscribe to analysis as a useful management tool?

In some occasional years of very low usage I skip the year end oil change. Probably should do it annually but...

pete

After I got a report that said there is some salt water in the oil, I changed the heat exchanger and then the oil. Had I just changed the oil at regular intervals would I keep the salt water from hurting the engine as the exchanger leaked faster.

I have read LOTS of these oil change threads over the years. I think the "hours" recommendation are just a a CYA thing from the manufacturers. It is like the sticker the place that changes my car oil sticks on the windshield saying to change again in 3000 miles. No harm in doing that other than to your wallet, but does it really make any difference?

In this case a 100 hours could mean 2000 miles at 20 or only 700 mile at 7. Does that seem to need the same oil change frequently?

Recently got the used oil analysis back from from diesel in the truck. The report was good and the oil I took out of the truck was still good.

Oil was in use for 11,500 miles. The manual says to change at 5,000 miles for highway driving. Normally, I change around 15,000-16,000 miles, and I am still getting rid of good oil.

The oil was in use for almost 3.5 years. I changed the oil before the pandemic hit, then did not drive very much during lock down, and lost track of time on the oil.

Per the oil test results, I could have kept the oil for another 5,000 miles, at a minimum, which likely would be another year or so.

How one uses the engine impacts the oil and when the oil needs to be changed.

Later,
Dan

As,said by many hours is the wrong metric to use concerning engines. For engines many think how much fuel goes through the engine makes more sense. Similarly for anodes hours is wrong. It doesn’t matter if the boat is sitting or moving whenever you have dissimilar metals sitting in an electrolyte (salt water) there’s a risk of corrosion as it’s a battery. So for anodes it’s time not hours. The products of combustion are water and CO2. Even with common rail combustion is incomplete. Of course that’s worst for naturally aspirated mechanical engines. Friction (and wear) primarily occurs at start up and when lubrication isn’t keeping up adequately with internal motions of the engine components. A engine running at 1200rpm adequate to produce oil pressure in excess of lubrication needs is having less wear and stress on oil days on end then an engine run 6-8 hours 2 or 3 times a week at varying loads . In the first case oil viscosity is ideal as is oil flow compared to load. In the second case not so much. Most of us have M4 or M3 engines. Most of us use our engines intermittently. Many of us have SD hulls and widely vary engine and turbo loads. In short we do what we can in our use pattern to maximize wear. Few of us can monitor fuel usage beyond looking at it instantaneously on our fuel flow gauges or looking at total gallons purchased per unit time or tank gauges. We do log fuel use in our log as do many but not the multi factorial information of fuel use c/w engine and turbo load. Oil and it’s additives breakdown with high temp and load. Particulate and contamination from incomplete combustion in the main. To my thinking there’s too many weeds to find the flower. I don’t have the inclination to sort off how far I can go before a oil and filter change. I just want to know I’ve not gone too far. So I take the simple way out and use hours to determine intervals (knowing it’s wrong) and even when it might be excessive due to low use change oil filters at 6 m.
If expense rises would get a centrifuge and stop discarding oil . If specing a high use blue water boat would install a centrifuge in order to be able to carry less oil in storage.

dannc said:

Recently got the used oil analysis back from from diesel in the truck. The report was good and the oil I took out of the truck was still good.

Oil was in use for 11,500 miles. The manual says to change at 5,000 miles for highway driving. Normally, I change around 15,000-16,000 miles, and I am still getting rid of good oil.

The oil was in use for almost 3.5 years. I changed the oil before the pandemic hit, then did not drive very much during lock down, and lost track of time on the oil.

Per the oil test results, I could have kept the oil for another 5,000 miles, at a minimum, which likely would be another year or so.

How one uses the engine impacts the oil and when the oil needs to be changed.

Later,
Dan

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I agree with this philosophy. Just changed the oil in my 2010 Jeep Grand Cherokee with just 20,000 miles and 3 years on it. I use the same philosophy with my boats. I have engines running since 1983 and I have never had an oil related problem with any engine and my engines are clean. I run from 15hp Hondas to 1350 hp twin turbo MTUs. How you use the engine can affect the term for change. I think oil change specs are way too stringent, but after all the BS, you have to decide what you want to do. I personally am very intimate with my engines, watching them, listening to them and tinkering with them all the time.

Contamination from moisture over time probably does more oil damage than most else.

Nomad Willy said:

Contamination from moisture over time probably does more oil damage than most else.

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Which is probably from short engine run times and more common I would think to a sailboat coming/going than a power boat. If it even really is more than a myth.

Nomad Willy said:

Contamination from moisture over time probably does more oil damage than most else.

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Yes important to consider. Think boats that aren’t used frequently have more troubles in all aspects including this than boats that are used.

I think/fee boat engines not used often enough suffer more from internal rust than from water condensation in the oil

SteveK said:

Have the oil tested and let the report tell you if it needs to be changed. Oil and engines have come a long way since the replace annually opinions were valid. I use Blackstone.

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The oil testing is cheap compared to changing it and filter.

Don L said:

Which is probably from short engine run times and more common I would think to a sailboat coming/going than a power boat. If it even really is more than a myth.

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https://www.machinerylubrication.co...dergo this process is known as hygroscopicity.

"Oils by nature are hygroscopic, which means they absorb moisture from the air. The tendency of an oil to undergo this process is known as hygroscopicity."

Nomad Willy said:

Contamination from moisture over time probably does more oil damage than most else.

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My research indicates it is combustion products combining with the moisture in oil that causes the acidity which leads to faster corrosion than water alone.

Thus.... I am guessing the reason why many manufacturers recommend annual or semi annual oil changes assuming the motor was run at least a bit and not pickled.

There’s a thread now on water in the engine oil.

Nomad Willy said:

There’s a thread now on water in the engine oil.

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Already responded there too.

Once upon a time, I had to drive a route that I called The Valley of Death. In The Valley of Death, one could sit for 10-30 minutes idling in traffic for a total trip time of 45-90 minutes. There certainly was no load on the engine during that idle time but the rest of the trip was at rural highway speeds of 55 mph.

The lesson was that the idling was putting fuel in the engine oil. While the amount of fuel did not exceed specifications, who in the heck wants fuel in your engine oil. Thankfully, I did not have to continue to drive into The Valley of Death, otherwise I would have had to change oil sooner. The lesson learned was that idling can really mess up your engine oil, which is why the manual says to change the oil at 2,500 miles in city driving, aka idling.

Any boat that is idling for any length of time, there is a good chance that fuel is in the oil and the only thing to do, is change per the manual or get a used oil analysis.

Later,
Dan

Last year I did 9 engine oil changes. With each change, I have Blackstone oil analysis done. Couple of years ago I changed engine oil manufacturers as I wasn't happy with John Deere’s oil. Had reduced the interval to lower elevated wear metals. Decided that last summer I would increase the intervals as the new oil had bottomed out the wear metals.

To answer the question on what difference does the intervals make, you are only guessing without oil analysis. For my use, I increased the intervals modestly and did 2 or 3 changes at that interval period. I reached a point where the wear metals were increasing at a faster rate than the time in hours. While I can't say that hurt the engine, it indicated to me that the oil wasn't working as well. Put it another way, if you graph wear metal levels over time, when it stops resembling a flat line and starts curving upward, you have to wonder whether the oil is the issue or suspended wear metals are increasing the wear on the motor parts.

An oil and filter change including Blackstone oil analysis cost me around $90. I certainly wouldn't have minded going longer between oil changes, but not at the cost of increased engine wear.

Hindsight is 20/20. If I were to do it over, I'd probably install one of these and paid for it in increased oil change intervals.

https://www.kleenoilusa.com/

Ted

Environmental Issues

I am surprised that there hasn't been more studies on this given the consequences of everyone changing oil in all vehicles that require it so frequently. I was told by many mechanics " the recommendations are for the older oils and were never updated, even todays 30 wt oil is far superior to what we had 10 years ago".

I go by hours on the boat or miles on the cars and ignore the one year rule.

On this subject, I have always used Rotella but recently have heard that it is no longer a preferred oil. Any opinions on that?

ronobrien said:

On this subject, I have always used Rotella but recently have heard that it is no longer a preferred oil. Any opinions on that?

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I use Rotella and never had any problems.

Generally if something is in consistent use, I don't worry about oil going past a year unless it's seeing a lot of short runs. If it's going into off-season layup and is at or above 1/2 the hours or miles recommended, then I'll typically change it. If it's hardly been used, I'll leave it alone.

Not sure where Rotella fell out of favor....haven't seen that in forums I watch.... have a source?