Older Marine Diesel - What Oil?

[wingcommander]

Hopefully a young 39 year old Bukh is still purring away. Well oiled.

 

[Poignard]

Hopefully a young 39 year old Bukh is still purring away. Well oiled.

Mine was installed in 1982 and still runs smoothly.

It is currently enjoying a diet of Duckhams Classic Q 10W-40.
Duckhams Classic Q 10W-40 - Duckhams

 

[TNLI]

Engine is a 28 year old Bukh DV20, which is using moderate amounts of oil (lots of little leaks rather than burning it, nothing catastrophic, just means I have to keep topping up, about 0.5 litre of oil every 15 running hours at 70% revs, more frequently if have to give it some welly to punch through a chop).

I've been topping up with 15W40, but should I be using HD30 - a thicker oil for older naturally-aspirated diesel engines - or doesn't it make any real difference?

Thanks

BUKH do list a seriers of different oils for different operating temperatures, but that list is for engines that are in good condition and not burning or leaking oil.

15W40 is probably similar to an SAE 30 when warm, but the SAE number covers a range and is for specific temperatues. The relationship of viscosity vs SAE number is not linear, so for example a 5w40 will be thinner when warm than a 15w40, and an 0w30 thinner than an 0w40 when very cold.
Also just to cofuse the matter, single grade oils do not contain VI additives like multigrades, and those additives do weaken an oil in terms of how resistant it is to high temp shearing. That often results in an SAE 30 finishing up as thick as a 15w40 when warm at the end of the oil change interval, assuming the oil is not subject to fuel contamination. In other words the SAE 30 will last longer.

If you have an old problematic donkey, try an oil designed for diesels that are in a bad way. Mobil make a 10w60 EL, (Extra Life). It's only just inside the SAE 60 range, so more of a 10w50 in the real world. That's a great oil with seal conditioners and lots of extra additives to help an old donkey.
The other option would be a major brand 20w50, (Acea B4), and by major brand I mean, Liqui Moly, Castrol, Mobil, Shell, Duckhams or Millers. Also I would include a number of other large oil companies when overseas, preferably those listed by the engine manufacturer.

I currently use Mobil Delvac 10w40 EXP Extra, (Acea B4), as my old lifeboat now has a BMC 1500 and Delvac was listed, although the 1230 version, (There are about a dozen different versions of Delvac, so be careful which one you order), was a single grade 30 that is no longer in production.
Finally don't forget that the quality of the oil filter is just as important as the oil type. I only use Mann, Bosche or Mahle made in Germany oil filters. Mobil also make good oil filters in the USA, but they are expensive extended life ones that don't seem to fit older diesels.

Finally stop leak additives do work unless the issue is a worn metal oil seal next to a hot turbo feed line. The only company I trust if I get forced into using an oil or fuel additive, is Liqui Moly. Their additives do what they say they can do, the Germans don't tell or print Porkie pies.