Dinosaur or partial synthetic?

[partingclouds]

I know it's been hashed about, but I'd like to hear more opinions on the subject of the proper oil for a Yanmar 2QM20 which is 40 years old and still running very well. Conoco 30-weight or Motomaster 10-30 partial synthetic?

Thanks!

[ErikFinn]

That old one definitely does not need synthetic and I would stay away from partials also. Mineral oils are not expensive and do a totally good job if changed within the schedule. Some car engines have started to leak from seals after changed to synthetic and then going back won't remedy the problem. If it ain't broken don't try to fix it.

[partingclouds]

Thank you, Erik!

[dcstrng]

Originally Posted by ErikFinn

If it ain't broken don't try to fix it.

I think this is the most logical solution... We generally want to "do-right" by our various engines and "oil threads" run rampant through marine, aircraft, motorcycle, automotive, chainsaw, lawnmower (etc., etc.) worlds, but for most occasional users are more philosophical than physical. It goes without saying the modern lubricants (be they dino or synth) are generally superior to their counterparts of decades before. I've twice tried to "convert" a formerly dino-lubricated engine to synth had subsequent leakage problems that went away after going back... nothing catastrophic, but a nuisance. On the other hand I've "converted" several others with no apparent issues, so... My personal take is that those of us with recreational engines probably tax them more from disuse, intermittent-use with extended periods of idleness, than any lubrication magic will cure (short of actually pickling the engine).

[Cheechako]

My opinion is you want to change oil often in a diesel to get rid of the carbon etc that builds up. So no point in paying for synthetic.

[hellosailor]

"Some car engines have started to leak from seals after changed to synthetic and then going back won't remedy the problem."
Yeah, that's been both proven and debunked. What happens is the new synthetics are high detergent and better detergent, as well as more "slippery". So the new oil is cleaning out the crap and coke that plugged up the engine, and when you clean it out and have a more slippery oil in there, it is more likely to slip past old deteriorated gaskets.
On the other hand, you may also notice engine speeds go up and economy/performance go up, as the new synthetics usually will lower internal friction by a measurable amount.
It isn't a "one size fits all" solution. Whether a synthetic is a good idea will depend on whether the oil is rated for diesel use, whether it meets newer specs (which affect how well the additives perform, friction reduction, etc.), and then of course whether the engine is being used a lot, or so infrequently that you'd just be throwing out the oil more often than it needs to be changed. And of course if the engine burns oil, synthetic gets way more expensive faster.

[Locquatious]

At the risk of being slightly off topic, it is worthwhile to mention that when lubricating devices other than engines, synthetic often works better. For example, I clean my own winches, though perhaps not once a year. Regular greases consist of a mixture of molecular weight oils that when combined develop a desired viscosity. This means that low molecular portions of the grease can evaporate or become solubilized. That is, the the grease dries up and leaves high molecular weight goo on the gears that does not lubricate as well and is much harder to clean. Synthetic grease has a narrower molecular weight distribution and doesn't dry up. It tends to last longer and is much easier to remove when you finally get around to the winches.

[NevisDog]

I was told the local lifeboat with twin big old caterpillars could not sustain full throttle due to overheating. Switched to synthetic and no more overheating, plus increased top end revs to boot.

[Djarraluda]

My old boat had a Yanmar YSE8 and the Yanmar data specifically stated to stay Mineral,. I was advised to stay with straight single grade and not use a multi grade either, but the Sydney temp range is pretty benign so winter starts we’re still virtually instant

[Hoodsail]

Not a yanmar, but in my 1978 Westerbeke w-30 I use rotella 10w-30 oil. Owned her since 2015 and the original Operator's Manual states "Select readily available lubricating oil with A.P.I. spec. CC or CD and SAE# suitable for your operating area". Change oil and filter annually just prior to going on the hard for the winter here in new England. So far so good.
thnks
dave

[sailorboy1]

I've read the articles for years now and the synthetic just always wins out. So I just recently decided to go to Rotella for the engine and generator. The extra cost is just so minor in the big picture.

[a64pilot]

I wouldn’t use either of those oils.
Never heard of them, I’d stay with Rotella as it’s widely available or Delo, both excellent oils. If your in Europe seek out a good well known truck oil.
The key is frequent oil changes moreso than synthetic oil. Our oil doesn’t break down, but gets loaded with soot, you could go with a good bypass filtration system and then syn would make sense, but it’s tough to beat a good straight grade oil and change it often, and the older the engine is, the more often if needs changing due to increased blow by.
However Rotella T6 is an excellent oil, you can’t go wrong with it either.

[SeaBreeze-1]

While my manual says to use a straight 30 weight oil, I actually use Rotella 15-40 in my 3QM30H and it works perfectly fine. It works well for cooler morning starts in the relatively cooler climates that we have on the Great Lakes. However, if you are now in, or are planning on heading for the "little latitudes", it might be best to keep with a straight 30 weight oil. The engine could possibly burn a little multi-grade if it is too tropical outside.

The debate over synthetic continues to rage on and while it certainly won't hurt your engine, conventional oil is changed so often in a boat as compared to a car that you might not realize any significant benefit from the extra cost. My engine uses 7 litres per change so the price difference is pretty significant.

[billgewater]

Ever wonder why engine builders advise the use of specific oils?
My own experience was with a Ford 590 e series 6 cylinder engine. (Dagenham, England 1962)
The handbook explicitly states the use of a mono-grade oil with variation only dependent on ambient temperatures..
Unfortunately I took the advice of a local diesel engineer who advised me to use a multi-grade oil.
The engine consequently blew blue smoke in clouds - for ages. So I went inter-netting and found an old chap in Ireland who used the 4 cylinder version of these engines to run small trains around peat bogs.
He was flabbergasted and chided me considerably - although his accent was a joy to listen to.
He stated (and I hope his rationale was correct) that these engines actually relied on some carbon build up on the rings and the detergents in multi-grade oils removed this carbon with the consequent sump oil burning.
I dumped the multi-grade and reverted to the recommended oil. Many many hours later:- no problems.
My advice is to contact the engine manufacturer. That way you are covered should anything go wrong. Hopefully.
Changing oil may also have repercussions on cooling, sealing and oil filtering. Beware.

[Compass790]

I wouldn't sweat it too much. We have a 1982 Yanmar YSM8 & use mineral 15w-40 in both engine & gearbox because of the cold start advantage & the price. I worried less tho about oils after reading this :Consumer Reports:Truth Motor Oils- July 1996.
I still change it according to the recommended hours as agree with other posts about carbon buildup.