Diesel Engine Oil Change Frequency?

[Dockhead]

Originally Posted by a64pilot

Synthetic oil of the correct type and viscosity will not harm any internal combustion engine.. . .

There is some controversy about that.

See for example: Oil for yacht engines – Cox Engineering

There is some information -- how credible everyone will have to decide for himself -- that synthetic oil increases the risk of bore glazing on certain engines. In any case, Yanmar do certainly forbid the use of synthetic oil in many of their engines (it is specifically permitted for certain other of their engines). Why would they forbid it, if "synthetic oil . . . will not harm any internal combustion engine"?

Whether it's harmful or not is separate from the question of whether it's worthwhile or not.

Considering how much soot (which is highly abrasive) and other stuff our oil is asked to absorb, I think the lubricant molecules themselves last far longer than the oil can hold soot. So spending money on a type of oil whose whole purpose is to make the lubricant molecules last longer seems pretty pointless to me, even if it is not actually harmful (which is debatable). Frequent oil changes on diesel engines seems like a really good idea to me -- keep that oil clean!

[a64pilot]

I have read that, and while most seem to consider this guy a guru, I don’t buy that a high TBN will cause the cylinders any harm.
High TBN is what has made Diesel oil, Diesel oil since I’d guess WWII.
New formulations of Diesel oil is much lower in TBN, I doubt you can buy a high TBN oil now. Reason is the metals used to achieve the high total base number (often zinc) will poison many if not all the catalysts in modern pollution control systems, and in theory since we burn ULSD, the low sulphur leads to low acid, so you don’t need as much base to neutralize acid that isn’t there.

[a64pilot]

I’m sure huge numbers of gallons of Shell Rotella T6 is sold yearly, it is their premium product, and if it caused problems there would be a class action lawsuit, wouldn’t there?
Or Shell would pull the product, make changes or put a warning of don’t use in Boat motors.
None of that has happened, and this is not a new oil.
I have been reading about the sins of synthetic oil for the last 40 years, with all the hoopla about how you can’t break in an engine with it, it will cause leaks etc. all from experts, and all of it false.

[a64pilot]

I’d like to see where Yanmar forbids the use of Syn oil.
Not saying I don’t believe it, but I would like to see it especially if it has any reasoning behind it.

[Stu Jackson]

Originally Posted by a64pilot

>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>
...or put a warning of don’t use in Boat motors.>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>

One "qualifier" here is that most, if not all, of our "boat motors" are "just" tractor engines shoehorned into our boats.


Least my Universal M25 is. My local Kubota tractor store is very, very handy and useful.

[Pyxis156]

Ken, a data point:

We have a 2008 Yanmar 4JH4-HTE turbocharged 110HP with almost 1700 hours on it. For the first four years the original owners used non-synthetic 15W-40. They kept meticulous logs and were religious on changing the oil every 200 hours.

For the last 6-years since we bought it, with the exception of the very first oil change I did using non-synthetic oil, I have used 5W-30 synthetic oil. I had an oil analysis performed on the original (non-synthetic) oil and have had oil analyses performed on each on my oil changes. The oil analyses indicate slightly lower levels of engine wear (nothing dramatic) with the synthetic, though just two datapoints for the non-synthetic oil is not definitive.

This winter I had a diesel mechanic show me how to adjust the valves and he commented on how clean things were inside the engine given the hours... “looks like new”. Probably more attributable to the regular oil changes than the type of oil.

Some anecdotal evidence: despite dropping in viscosity, my oil pressure is still above the minimum (and yes, my manual does say 10W-30W is okay to use). The engine starts slightly faster (always one crank vs. two or three before) and runs slightly cooler (especially at higher RPMs), but again still within the Yanmar specs. Using an infrared thermometer, the turbo is definitely running cooler. I use almost no oil (the level might drop 1/8” between oil changes) which I interpret to mean my cylinders and rings are happy. In my mind, all good things.

Hope this helps... and congrats on your new Oyster!

[Dockhead]

Originally Posted by a64pilot

I’d like to see where Yanmar forbids the use of Syn oil.
Not saying I don’t believe it, but I would like to see it especially if it has any reasoning behind it.

The manual for my 4JH3 HTE specifically mentions it. It is also quite specific that only API-CD should be used, although I think there was a service bulletin saying that CF-4 can be substituted.

I do note however that some of their newer engines specifically permit the use of synthetic oil.

I think these recommendations are worth taking seriously -- and they are likely to have something to do with the composition of the piston rings, the clearances, and maybe treatment of the cylinder bores.

I would be very reluctant to assume that I understand more about what kind of oil my engine needs, than the maker.

[transmitterdan]

At least some turbo chargers can apparently be harmed by synthetic oil. The story I was given was the synthetic oil has less "clingy" ability. So all the oil drains down to the sump. At startup the turbo spins up with nearly dry bearings and they wear a lot before the pump can get oil to them. Dino oil clings and doesn't slip away so easily. I got that info after losing a turbo on a small gas engine. The mechanic berated me for using synthetic oil and produced the owners manual which specified the correct oil (not a synthetic).

Use whatever oil the engine manufacturer recommends. It is pretty good advice.

[transmitterdan]

BTW, we once had a super charged PWC. The manual went to great lengths to warn about not using pure synthetic oil. Only blended synthetic or non-synthetic was recommended.

[Cadence]

Originally Posted by a64pilot

Shell as in Rotella also makes an excellent synthetic 5W-40 T6.
I used it in my truck and my cars for years, and was using it in my boat as I had one oil for every motor, dinghy, Honda generator, generator etc.
Still run it in our little Mazdaspeed Miata turbo.
I still think it is an excellent oil, but now I am using straight weight 30W Rotella oil.
Rotella as it is very widely available. I think Chevron Delo is as good an oil.

I've never tried the synthetic Rotella. Being satisfied with the original. At the time I looked, it was four times as much and I could not see the economy since I knew I would not increase the oil changes by four fold.

[a64pilot]

Rotella T6 on Amazon $22 a gallon
https://www.amazon.com/Shell-ROTELLA...w-40+synthetic
T4 15w-40 $15 bucks a gallon, it’s a little less but not by much
https://www.amazon.com/Shell-ROTELLA...w-40+synthetic

As far as being bad for turbos etc. what high end high performance automobile doesn’t come with Syn as a factory fill?
I believe almost all Toyota’s, Honda’s come with and recommend 0W-20 oil, and guess what? I don’t think it can come any way but synthetic, maybe some blends.
I don’t know, but bet maybe the huge sludge lawsuit Toyota went through maybe had something to do with them requiring Syn oil, maybe?

Far as CD oil? I’d love to run it, that was the old high TBN stuff. Anyone know where a I can get some? How about plain old Dexron cause that is what my tranny calls for.


I’m not trying to get you guys to run synthetic oil, I don’t for the first time in decades. If you want to believe it eats turbos and all the other bad things associated with it, without any of that actually happening, we’ll go ahead.
There are just too many people running it in every imaginable engine out there, that if it did bad things, there would news coverage and lawsuits, just like Toyota went through with regular oil, except I have never heard of one, have you?

[Cadence]

Originally Posted by a64pilot

Rotella T6 on Amazon $22 a gallon
https://www.amazon.com/Shell-ROTELLA...w-40+synthetic
T4 15w-40 $15 bucks a gallon, it’s a little less but not by much
https://www.amazon.com/Shell-ROTELLA...w-40+synthetic

I'd buy it by the case of gallons. A case of reg. Rotella T was $25 one of synthetic was $100. Significant when one case is one oil change.

[a64pilot]

Not sure where your buying your oil, but regular oil usually goes for about $70 for 5 Gls and Rotella Syn for $110 or so. Probably cheaper by the bucket, just haven’t seen it that way.
https://www.tractorsupply.com/tsc/search/Rotella%20t6

[a64pilot]

Other things.
No oil if the viscosity is correct will make an engine harder or easier to start, make it run quieter, smother, faster, or give any measurable difference in fuel consumption, nor make it run cooler etc.
If any of this were true, then would any responsible manufacturer recommend any other oil than the one that did all those things for their engine?
At one time manufacturers would have sold their soul for 1mpg, not so much now cause people don’t care and CAFE standards don’t really exist anymore.

Good Syn oils can tolerate much higher temperatures without breaking down, can have better detergent packages and allow longer change intervals.
However none of that is really applicable for our little sailboat engines, except maybe the detergent package, good regular oils have good detergent packages too.

[a64pilot]

On the turbo thing, if you have a highly stressed turbo engine, especially if it’s not water cooled as many new one are, Syn oil is by far the better oil.
Why? Higher temperatures and especially the resistance to coking on shutdown is why. A turbo when you turn the engine off, the hot section is still at exhaust temps, when you shut down oil flow stops, often oil is then cooked into coke, coke destroys the center section bearing, even more so of its not a ball bearing turbo, most are not.
That is why you should always idle a turbo before shutdown, to allow the hot side to Cool as much as it can.
No turbo will have any significant rotation before oil flow is established on start up, average turbo doesn’t even rotate at idle.

However that doesn’t describe any of our little sailboat engines, and they way we operate our boats pretty much guarantees a long low power or idle before shutdown anyway.