Synthetic oil for diesel

I am considering changing to a synthetic oil for longer periods between oil changes. This is the oil that appeals to me - Shell ROTELLA Rot T6 Synth 15W40. Has anybody switched to synthetic oil for their diesels? I have two 3208 cats, and aNorthern lights 16k gen set.

Thanks,
Bud

It is highly recommended to change oil annually even if hours aren’t met. How many hours per year are you accumulating?

Bud said:

I am considering changing to a synthetic oil for longer periods between oil changes. This is the oil that appeals to me - Shell ROTELLA Rot T6 Synth 15W40. Has anybody switched to synthetic oil for their diesels? I have two 3208 cats, and aNorthern lights 16k gen set.

Thanks,
Bud

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Why do you want to use synthetic oil?

I have been using synthetic oil in my truck and tractor engines for decades for better cold weather performance and for extended oil change schedule.

Few topics will excite more opinions than oil type! Here's mine:

As sunchaser said, annual oil changes (at minimum) are preferred.
CAT 3208 naturals will do just fine with Rotella T4. If turbocharged, then T5.
Unless you find a smoking good deal for T6, you'll save a bunch of money with T4.

KnotYet said:

Few topics will excite more opinions than oil type! Here's mine:

CAT 3208 naturals will do just fine with Rotella T4. If turbocharged, then T5.
Unless you find a smoking good deal for T6, you'll save a bunch of money with T4.

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Interestingly, I've ended up switching a few things (including the boat) to semi-syn (T5 or Delo XLE) because for the last couple of years I've found it's the same price or cheaper than the dino equivalent (T4 or Delo SDE).

rslifkin said:

Interestingly, I've ended up switching a few things (including the boat) to semi-syn (T5 or Delo XLE) because for the last couple of years I've found it's the same price or cheaper than the dino equivalent (T4 or Delo SDE).

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Oil purchasing, like most consumables, will always be a moving target.
Today at Walmart I found 5 gallons of T4 selling @ $71; T5 @ $94 and T6 @ $102...
All marketing ploys aside, non-synthetic is probably cheaper to produce than synthetic.

I use full synthetic in my HP SUV because that is what the manufacturer calls for. I use either shell T4 or chevron Delco 400 in my Cat 3208’s because that is what the manufacturer calls for.

For over twenty years I have only run synthetic in all my diesels. To me, extending the interval between oil changes is a side benefit, but I seldom push the interval, if at all. The reason I like synthetics is their superior lubricity, which I measured with a digital oil temperature gauge. In the same engine under identical operating conditions, synthetic oil ran about 10 degrees F cooler than dinosaur oil, even though engine coolant temperatures were the same. That tells me synthetics reduce friction, which translates into reduced wear.

I believe in using the engine manufacture's recommended oil. If it calls for CAT 40W oil then I go to the CAT dealer and buy their oil. The way I see it is with the cost of engines I don't want to save a few dollars on oil and spend more on engines.

fgarriso said:

I believe in using the engine manufacture's recommended oil. If it calls for CAT 40W oil then I go to the CAT dealer and buy their oil. The way I see it is with the cost of engines I don't want to save a few dollars on oil and spend more on engines.

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For engines with very specific oil needs, sure. But for many engines, there's nothing all that special about the manufacturer's oil and plenty of other oils are suitable, or the manufacturer lists certain specs that the oil needs to meet, but their own oil may not be the best out there. Just a matter of figuring out what's suitable or not. And in some cases, the spec was set 40 years ago when the engine was built and there are better and more suitable oils available now.

Outside of a 2 stroke Detroit, it would take a whole lot to convince me to use a straight weight oil in anything at this point. Most things that spec straight weight are old enough that multi-grade oils weren't very good at the time and they had concerns, but that's not necessarily valid with modern oils. I'd much rather run a 15W-40 than a straight 40 in just about anything that specs straight 40, for example.

I do not nor have I used synthetic in my Cummins V555 engine M. I looked into it years ago and decided there was no saving either $$ or effort unless the engine was very new and started with the synthetic from new. I would still have had to use the same oil change intervals. Mine was not new and is even less new now.

Even so the oil tests come back darn new perfect except for one bought with diesel in the crankcase. Leaking injector(s) and now back to very favourable tests.
It shows somewhat over 7,000 hrs , perfect oil tests again and 47 yrs old.

But otherwise I don't buy it unless something like very high OR very cold temperatures require the synthetics.

I use and have used for many years a 15.40 oil.

But to each their own, your choice.

Blissboat said:

... In the same engine under identical operating conditions, synthetic oil ran about 10 degrees F cooler than dinosaur oil, even though engine coolant temperatures were the same. ...

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Reducing engine and ER temperature would be a worthwhile reason to use synthetics all by itself...

I posted a similar question last year and decided on T5 (Synthetic Blend) for my ancient Perkins 4.236. Reason was not price but rather test results were slightly better for T5. But I really don't think it makes much difference - these are all fantastic oils - far superior to anything available even 20-years ago and will serve your engine well long into the future.





Peter

As with many of life's choices, the middle path is often best.

My Bacchus website - Nautical Links section has an article by Cox Eng re Lubricants for Yacht Engs.
It is the most relavant article I have seen and follow the recommendations.
My opinion is more frequent changes with Dyno oils is superior to running (contaminated) syn oils for longer periods. Running diesels adds carbon to the oil and linger runs = higher contaminant levels... not desirable IMO.
Run dyno & test for Running more than 12 mo when eng hrs are low has been my practice. My tests show 12 - 24 mos is more than acceptable for lo hrs & dyno oils.
Others feel syn is better but most eng mfgrs caution against extending run hrs when using syn.

sunchaser said:

It is highly recommended to change oil annually even if hours aren’t met. How many hours per year are you accumulating?

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I've heard this for years - that oil should be changed every year even if not used much. I've heard a couple justifications for it - acid forms over time due to condensation, or the additives can settle out. I wonder if this is true (or if it was true, have modern oils changed and it is now an old wives tale). I've certainly seen OEM recommendations along these lines, but never justification why. Cynic in me wonders if urge to change is to sell more oil, or at the very least has no cost to the OEM so why not make the recommendation.

Has anyone ever seen empirical testing that shows oil degrades just by sitting in an engine? The TBN number should degrade if acids somehow form. Thoughts? Oil is pretty stable stuff - I don't recall a "use by" date but I've never looked closely.

Peter

Peter
The data I go by is my own oil analysis results. I feel the acid build up is a myth that's often repeated. Acids don't "build up" from sitting they build up from running and the products of combustion and yes.... thats what TBN indicates and the additives are there to counter.
Short runs especially ones that idle a diesel simply to " circulate the oil" do more harm than good but I have read posts if many RVers that "run" their diesels every month while in storage to "charge" the batteries and "lubricate" the engine. I have never seen an eng mfg recommend those practices but it "feels like the right thing" for some.

I have seen one study that indicated SOME degradation over extended time periods... on the order of 5+ yrs but that's not what these discussions usually revolve around.
I

I've never really stuck to the 1 year change thing. On most engines I'm happy to let them go 2 or 3 years if the use is low enough. But if it's used seasonally and it's already 60 - 70% of the way to a change interval at the end of the season, I'll just change it out of convenience instead of doing a mid-season change the following year. Plus, putting it away with clean oil certainly won't hurt it anyway. If it's used year round but use is light or if it's seasonal but hardly has any hours on the oil, then I'm not going to dump the oil early. Degradation from just sitting in an engine shouldn't be much unless there's some ugly environmental conditions (in which case the engine is likely suffering in other ways).

When in doubt about how long to go between changes, analysis is definitely the answer. The combo of oil, engine, and usage patterns dictate how long you can go. Some engines and usage patterns are harder on oil than others, so some will need a change sooner. And some oils hold up longer, particularly in engines that are hard on oil.

Keep in mind, as much as there are risks with going too long, if the oil filtration is up to par and the oil is still doing its job for the longer change interval, soot buildup, etc. shouldn't be a significant concern. And there are risks with changing too often as well. Unless you can get the filter and oil passages to it, etc. completely pre-filled then every oil change is a dry start where it takes a couple of seconds to build oil pressure and that can cause extra wear.

mvweebles said:

I've heard this for years - that oil should be changed every year even if not used much. I've heard a couple justifications for it - acid forms over time due to condensation, or the additives can settle out. I wonder if this is true (or if it was true, have modern oils changed and it is now an old wives tale).

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Bacchus said:

Peter
The data I go by is my own oil analysis results. I feel the acid build up is a myth that's often repeated. Acids don't "build up" from sitting they build up from running and the products of combustion and yes.... thats what TBN indicates and the additives are there to counter.

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rslifkin said:

I've never really stuck to the 1 year change thing. On most engines I'm happy to let them go 2 or 3 years if the use is low enough. But if it's used seasonally and it's already 60 - 70% of the way to a change interval at the end of the season, I'll just change it out of convenience instead of doing a mid-season change the following year. Plus, putting it away with clean oil certainly won't hurt it anyway. If it's used year round but use is light or if it's seasonal but hardly has any hours on the oil, then I'm not going to dump the oil early. Degradation from just sitting in an engine shouldn't be much unless there's some ugly environmental conditions (in which case the engine is likely suffering in other ways).

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Can't speak to oils for OP's specific engines... but I can say that Rotella T6 5w40 is one of the few lubricants specified by our engine manufacturer. Seems to work OK.

But... it's not inexpensive, and if it weren't semi-mandatory I think I'd just be looking at whatever oil the makers (Cat and Northern Light, in OP's case) recommend... (Synthetics probably not on Cat's list for 3208s back in the day...)

And... then I'd be supplementing that with periodic oil analysis. We've homed in on every 200 hours for changing our main engine oil and filters... and that helps a bit since our main engine oil changes need about 16 gallons

.-Chris

One has to enjoy the never ending “quest” for easing off on boat maintenance 101. Some of us bought our boat new. Extended warranties, insurance etc on the engines require following manufacturers guidelines. Changing oil by the book satisfies these requirements.

On our Perkins Sabres/Cat3056 each oil change cost $20 for filters and $60 for oil. My industrial background clearly answered why oil changes by the book were important as big equipment up time was money in the bank.

Peter, to me the better question is why not change oil by the book? It is cheap and an engaging task. If it is too much effort then why have the boat with its all other attended needs?

BTW, when we sold our boat both engines’ oil analysis came back near perfect. It helped seal the deal. Yup, annual oil changes or more frequently, dependent upon hours, were performed. But, as usual, your boat your choice.

One has to enjoy the never ending “quest” for easing off on boat maintenance 101.

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As someone who DIY I will follow the suggestions of the oil analysis company. Nothing to do with avoiding maintenance. Sending in a sample to be tested will tell you if you need to change out the oil or not. It will also tell you if the heat exchanger is adding coolant or raw water. Changing the oil without a test will not.
We all have oil filters to remove harmful products. If you have the need, change the filter every year, change the oil after the test report says to change it.
Most boat engines on this forum come from an era when oil was not as sophisticated as it is today. Straight weights were called for, whereas now you can use multi weight.
Doing something on a timetable does not make it correct.

sunchaser said:

Peter, to me the better question is why not change oil by the book? It is cheap and an engaging task. If it is too much effort then why have the boat with its all other attended needs?

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Fair question. For me, between Ensenada and Florida, I will do around 5000 nms, approx 750 engine hours - 7-8 oil changes at the oft-stated 100-hour interval. To date, I've had a few runs where I've done 100-hours in 10-days or so. To further complicate the equation, getting high quality diesel oil is not easy. Getting rid of used oil isn't always easy either. I won't argue the expense, but will mention the environmental considerations of discarding oil that has a lot of life left in it (if that is indeed true).

For decades I've heard (and sometimes repeated) the 100-hour/1-year change interval guidance. In autos, for years the recommendation was 3000-miles which the oil change places still tout even though new cars often carry OEM recommendation of up to 10,000 miles with synthetic oil. Just feels like there the recommendations are not based on actual data trends; and are often promulgated by companies who have a vested interest in selling more oil or oil changes. As an example, Toyota recommends 10k miles between oil changes for many of their new cars, but their dealers routinely recommend 3k miles on the little reminder-sticker they paste on the inside of your windshield.

Oil has changed a LOT over the years. Project Farm YouTuber channel was given a can of 70-year old Quaker State motor oil that he had analyzed (click HERE and the YouTube will start at the discussion of analysis). It has no additives, no dispersants, and the TBN in this fresh oil is 0.4 - well below the 1.0 threshold.

Long way around the horn to say: given the improvements in lubricants, is the 100-hour/1-year guidance still relevant? Or are we just kicking-the can out of ignorance of better data?

I guess the best data would be some sort of trending showing decline of TBN vs engine hours. Sure, would vary by individual engine, but would be very interesting.

Peter

Sticking with short or recommended change intervals is a safe route, but not always necessary. Depending on the usage and oil in use, you may be able to go significantly longer with no issues. Especially with lots of running in a short period of time where the engine is up to temp for most of the running time. Someone who takes the boat out for a 20 minute run to a nearby anchorage and then comes back later a bunch of times in a year will chew up the oil in less hours than someone who is regularly running 8 hour travel days and not doing short runs.

On a long trip like Peter is describing above, I'd certainly want to send for an oil analysis after the first and maybe second change to determine how long I should go on subsequent changes.

My engines and generator also recommend a 100 hour change interval. I'll never stretch it past that for the generator as it doesn't have an oil filter. Same story with 50 hours for the dinghy outboard. But for the mains, when we crack the 100 hour mark one of these years (we've been close but never quite gotten there) I'll send off samples for analysis. I'd bet that we can go longer than the 100 hour spec without issue, it's just a question of how much longer (and I'm not going to guess at it without data).

I use Cat's SOS Fluid Analysis Lab. to do my fluid testing.
I just looked up the last 4 tests on my engine oil, which had between 190 and 240 hours on the oil at the time of the test. I, at the time changed the oil irrespective of the results.
The engines now have clocked 3700 Hrs. and the oil was always Rotella T4 15W-40.

In each report Cat said "Total Acid Number (TAN) and Total Base Number (TBN) are acceptable. Wear metal analysis indicates acceptable wear rate and other readings appear to be normal. Resample at the next service interval."

For me an engine oil change takes 4, 1R-0716 filters and 25 Gal. of oil. Total cost about USD $550 and 6 hours of work, plus disposal of the old oil. Lugging 5, 5 gal buckets up the ramp to the truck is, at low tide, no easy feat.

When would you change the oil, at some number of running hours, a specific date or when the lab said it is time, which admittedly would likely take multiple tests as to not overextend oil usage?

I'm

mvweebles said:

Fair question. For me, between Ensenada and Florida, I will do around 5000 nms, approx 750 engine hours - 7-8 oil changes at the oft-stated 100-hour interval. To date, I've had a few runs where I've done 100-hours in 10-days or so. To further complicate the equation, getting high quality diesel oil is not easy. Getting rid of used oil isn't always easy either. I won't argue the expense, but will mention the environmental considerations of discarding oil that has a lot of life left in it (if that is indeed true).

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For years, I have run extended hours/miles/time on my truck engine which is now getting close to 23 years old. The manual says to change the oil at 5,000 highway miles. I try to change around 15,000ish miles. Used Oil Analysis says I am throwing away good oil at 15,000ish miles.

If I had followed the manual, I would have used 42 quarts vs 14 for the same mileage. That is throwing away quite a bit of oil, money, and time for no good reason.

mvweebles said:

Oil has changed a LOT over the years. Project Farm YouTuber channel was given a can of 70-year old Quaker State motor oil that he had analyzed (click HERE and the YouTube will start at the discussion of analysis). It has no additives, no dispersants, and the TBN in this fresh oil is 0.4 - well below the 1.0 threshold.

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Blackstone Labs bought some old and ancient oil of Ebay years ago and tested it. The oil was still good despite the age. Some oils had similar additives as similar oils of today while other were different. I can't find that article unfortunately. But my take away is oil just sitting in a can is not really aging but what is in the oil can be different than today's oil.

mvweebles said:

Long way around the horn to say: given the improvements in lubricants, is the 100-hour/1-year guidance still relevant? Or are we just kicking-the can out of ignorance of better data?

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It is ignorance, but changing oil and filter per the manual, is the safest thing to do. A used oil test is not cheap, and certainly for some engines that don't hold much oil, just changing the oil could be the cheaper thing to do vs testing the oil. During the pandemic, my truck engine went over three years between oil changes. I did not mean for that to happen but that is life. I changed the oil with 10,000-12,000 miles on the oil and the used oil test said I threw away good oil. The numbers were as they should be.

mvweebles said:

I guess the best data would be some sort of trending showing decline of TBN vs engine hours. Sure, would vary by individual engine, but would be very interesting.

Peter

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What is indicating it is time, or not, to change oil is TBN for my engine. I have never had a low enough TBN that required an oil change. The TBN was still at a good level at 15,000-16,000 miles. Some other numbers were "aging" but still within allowable ranges. TBN does go down with miles/hours but I have yet to get the oil down to where the TBN is almost gone.

Now, I did not just say one day that I am going to run 15,000 miles in my engine and just put the miles/time on the oil. I changed oil per the manual, originally on 15w40 oil, then with 0w40 and 5w40 synthetics, and sent the oil off for testing. The lab said the oil was fine, try another X number of miles. So I did, and repeated the test. The lab said try another X number of miles until I worked up to the 15,000is mile mark. I can go longer on the oil but 15,000ish miles seems good enough.

I am also driving highway miles vs city miles and it does make a difference. Idling the engine, or not having the engine loaded correctly, has put fuel in the engine oil. That happened on my truck and tractor engine and showed up in the oil tests. Thankfully, the fuel was in the allowable range but who wants fuel in their oil... So how one operates the engine matters as well as the oil. The only way to really know what is happening with the oil/engine is to test the used oil.

luna said:

For me an engine oil change takes 4, 1R-0716 filters and 25 Gal. of oil. Total cost about USD $550 and 6 hours of work, plus disposal of the old oil. Lugging 5, 5 gal buckets up the ramp to the truck is, at low tide, no easy feat.

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Yeah... today's price at Walmart for a 5-gallon pail of T6 5w40 is $237, and we usually need three... which leaves some for check-ups or for next year.

FWIW, the cost isn't what really drives me, and some of the cost savings from 200-hour changes is eaten up by testing fees anyway... I just mostly don't like to waste oil that still tests fine.

-Chris

ranger58sb said:

Yeah... today's price at Walmart for a 5-gallon pail of T6 5w40 is $237, and we usually need three... which leaves some for check-ups or for next year.

FWIW, the cost isn't what really drives me, and some of the cost savings from 200-hour changes is eaten up by testing fees anyway... I just mostly don't like to waste oil that still tests fine.

-Chris

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See if you can pre-order T6 for pickup at your local Walmart like I can:
$20.34 per gallon in the 3-pack!

If you'd rather buy it in 5 gallon buckets there's this at Walmart for a few dollars more:

Our boat engine book said change the engine oil at 400 hours or annually provided ULSD is used. The oil change interval, by the book, lists PPM sulfur in the fuel as a guide. We changed between 200-300 hours.

Peter, with today’s ULSD I’d question the 100 hour interval on your old Perkins. Those old manuals were written before ULSD was available. Does the oil check ok after 100 hours?

Walmart DELO 400 is $18 per gallon.

So if you were going to change annaually, would you change when you haul out and let it sit with the fresh oil, or let it sit with the stale oil, and change it before you launch in the spring ?

Also, if oil expires, does that mean when I stock up on oil and store it in my garage it has a shelf life ?

KnotYet said:

See if you can pre-order T6 for pickup at your local Walmart like I can:

Shell Rotella T6 5W-40 Full Synthetic Heavy Duty Diesel Engine Oil, 1 gal (3-pack) - Walmart.com

Buy Shell Rotella T6 5W-40 Full Synthetic Heavy Duty Diesel Engine Oil, 1 gal (3-pack) at Walmart.com

www.walmart.com

$20.34 per gallon in the 3-pack!

If you'd rather buy it in 5 gallon buckets there's this at Walmart for a few dollars more:

Shell Rotella T6 15W-40 Diesel Engine Oil, 5 Gallon - Walmart.com

Buy Shell Rotella T6 15W-40 Diesel Engine Oil, 5 Gallon at Walmart.com

www.walmart.com

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Interesting links, thanks. I hadn't actually been shopping, just grabbed the first credible link I found to illustrate prices -- but the $237/5-gal price I mentioned came from a Walmart link just yesterday. The 3-pack price you found is much better, so I wonder why Walmart pricing is so weird.

Your second link is for 15w40 and we need 5w40, so that's not directly comparable. Still an example of odd pricing, $137-ish difference on the same day for nearly the same product.

See here: rotella t6 5w 40 - Walmart.com

Today's prices all over the map. One 3-pack price $61, same 3-pack also $97. Thw 2.5-gal bottle, $93, or $145 for a 2-pack of those, a 6-pack of 1-gal bottles, $55. Jeez...

I don't actually prefer the 5-gal pails; too heavy. The 2.5 bottles work pretty well.

When it comes time, I've usually shopped the net, and prices/availability vary between Walmart, Tractor Supply, various auto store brands, etc.

-Chris