Hitchcocks Forum

No big deal, but have several galloons of new SAE 50 diesel
motor oil left over from a smoky Mercedes 240D I once had.
Is this OK to use in our vintage motors, or simply too high
a detergent content. seems a reasonably good house brand, 'tis
a shame to throw it out unused. Current car is a gasoline Mercedes
with usual 10/40 oil not using a drop between changes

Hi Gordon: Well, depends on the state of the engine, if it`s fairly clean in there it should be alright; if it has a lot of carbon and sludge in there it might have the same effect as running with flushing oil; you would need to check the filter after a 100 miles or so to check how much crud the diesel oil has loosened. It could block the oilways. Personally, I wouldn`t use it in an old engine. In a rebuilt or new one, ok.

Why 'ruin the ship for a ha'peth of tar'? You might save a small amount of money by using this oil, but why risk any premature wear or damage to your engine? Better to use the correct stuff. Perhaps you know someone who could use the diesel engine oil and give them an early Christmas present? Regards, Paul.

Thanxs, lads, will leave the oil on a nearby quay
where the fishing trawlers come in, they prsumably
use marine diesel motors thas drink oil.

Might be worth a bucket of prawns.

Maybe keep a gallon to fry the prawns, like way back
in Oz, Leon!

Personally I'd not recommend using a mono-grade. I know the arguments - but would still not recommend a monograde. Certainly not one with a 50 viscosity - far too high. The stresses that will place on the oil pumps in particular at starting from cold will be very high. Could be a case of 'Penny-wise - pound foolish' - no offence meant!

I run em all on straight 50. A bit warmer here in NZ (although pretty miserable at the moment) in England I ran the M16S I had on straight 30 in winter (until I discovered black ice that is) and straight 50 in summer. Seemed to love it.

The older RE manuals recommended a straight 50 oil. If you're talking about a genuine vintage machine and a decent quality oil such as Castrol GP50 you should be ok. I ran my 1970's 350 Indian Enfield (where tolerances were measured in millimetres!) on straight 50 for many years without any problems. Not too sure about a modern Indian Enfield though, probably better with a 20/50.

I respect the views of those who have used a monograde - but can see no reason for using it at all. Can see no advantage and only disadvantages. I don't doubt that you can and may not have a problem because you did use it. But still don't see the point - that's after years of hearing 'I used it and it was OK in my engine'. Why? - what advantage?