Kubota Recommendations

[trbostjr]

Hello,
I own a boat with a 2005 Kubota Beta Marine 38.5 horsepower diesel engine. I'm posting here because I would classify this engine as heavy duty.
The original operator's manual states, "A good quality 15W/40 multigrade oil as used in most car engines will meet these requirements. Do not use Turbo Diesel Oil or additives."
The newest version of Beta Marine's manual from Beta Marine's website states, "Do not use lubricating additives and/or fully synthetic lubricating oil." Manual goes on to say, "NB: An acceptable alternative is a mineral based semi-synthetic lubricating oil with a content mix no greater than 30% being synthetic based."
I have used synthetic oil in cars, trucks, motorcycles, portable power equipment, tractors and other boats. This is a new one on me. Maybe when the motor was manufactured they might have restricted use of synthetic oils...but today? In their current manuals?
I stand ready to swap out the Mobil One 15W-40 for Rotella T4 15W-40 but I would love to know WHY Kubota stubbornly continues to publish this strongly worded recommendation. Am I missing something after 30+ years in automotive service and 25+ years of automotive instruction?
Thanks in advance.

 

[dnewton3]

First of all ... kudos on the posting restraint! First post since in seven years is quite the accomplishment.

About the only thing that would come to mind is that back in 2005, diesel oils and fuels had a lot of sulphur in them, relative to today. That sulphur combined with moisture makes for some nasty acid. But today's lubes (and fuels) have FAR less of a risk in that regard. Those concerns of 20 years ago probably don't apply now.

 

[wpod]

Synthetics are not needed when quality 15W-40 HDEO oil is used. the HDE)s oils are that good. [Freezing temps with out a block / pan heater makes a syn the better choice ]

 

[trbostjr]

dnewton3, No kudos needed. I use search and find answers usually. I understand about sulfur causing corrosion.
wpod, thanks for note on correct oil for temperatures. My son lives in Idaho, it was 17 F in Bellevue the other day when it was 63 in NC.
Why, why, why would Kubota insist on leaving that in their operation manuals after all these years. Are we missing something?

 

[doitmyself]

You might want to make an attempt to find someone knowledgeable at Kubota Corporation for an answer. Alternatively, maybe this has been discussed on marine forums?

Here is a thread about how Kubota went several years publishing tractor manuals that recommended NOT to use the then-current CJ-4 diesels oils: https://bobistheoilguy.com/forums/threads/kubota-do-not-use-oil-spec.274073/

It always amazes me how these giant corporations mess up something so simple. Sorry I cannot help with your conundrum.