Probably 15-40 or 20-50 oil. I tend to stick with semi synthetic rather than wholly synthetic. Thin slippery synthetic diesel oils were made for smaller high speed motors like modern Japanese 4WD diesels with small bore oil journals. An older design slow revving marine diesel can do with some good quality courser mineral oil in the mix.

Of course, this is opinion only. Any 20-50 diesel sold in Oz will satisfy or exceed industry standards. Just change the filter each time and change the oil a couple of times per year.

Depending on the engine's angle, the dipstick won't be accurate and some 'old' oil will sit at the back of the sump. All depends on where the he sump plug is, and whether you're using a suction pump to drain the oil.

From a mate that owns his own diesel injection business for 30+ years when he rebuilt my Perkins.

Single weight 15-30 (15 preferable, but maybe cold climates such as Tasmania 30w) non synthetic.


Modern hitech/turbo - then whatever the manufactures says.

Castrol mono 30
fixed!

MorningBird said..
Change a couple of times a year? How many hours do you do to warrant that?

My manual says change the oil and filter every 100 hours. That was based on oil made in the late 70s early 80s.

With modern oils and new filters I can't see there is a need to change it any more often than the manufacturer requires.

I have heard its not the hrs that count, its the time the oil spends in the engine . It gets corrosive the longer it stays in there .

SandS said..

MorningBird said..
Change a couple of times a year? How many hours do you do to warrant that?

My manual says change the oil and filter every 100 hours. That was based on oil made in the late 70s early 80s.

With modern oils and new filters I can't see there is a need to change it any more often than the manufacturer requires.

I have heard its not the hrs that count, its the time the oil spends in the engine . It gets corrosive the longer it stays in there .

Motor Oil can be or is hygroscopic, it absorbs moisture and moisture breaks down additives in the oil and also causes corrosion. It may be claimed that the more additives in oil, the higher possibility it has of absorbing moisture.
I have an oil can in the shed that I put left over motor oil in and in no time it goes milky. I have an identical can that contains machine oil and it is never milky

cavalier32 said..
For a Bukh 20 hp, should it be full synthetic or thereabouts.
Gary

Definitely not synthetic. Stick with what the manufacturer recommends. Preferably mono 30 grade but any of the cheap multi grades will do. 100 hours or every six months, which ever comes first. If your filter is hard to get to, change that once a year or every second change of oil. If you are doing lots of hours then an oil change once a fortnight is fine. Oil is the cheapest item you will put in your boat.

Old engines use old style oil. Flat tappet engines need at least 1200ppm of ZDDP

Thanks for all your advice it has been very helpful.
Great sailing everyone, hope to see you out there