best lubrication for long term engine storage?

[JonE]

I free'd off a newly built engine and one of the reasons for its inability to turn over seemed to be brown stains everywhere inside, on the new pistons, rings and so on. I'm imagining it was stored for two decades and the oil gradually dried out.
So, theoretical question perhaps, but which lubricant is least likely to create this sort of problem over time - or which might have caused this in the first place?
I've also noticed a pan of cam followers which I've left in diesel for a long time (to clean up) seem to have the same sort of effect on the top faces where they are exposed.

[Robert Leigh]

I am not recommending it but vegetable oil (Castrol R) has far better sticking properties than mineral oil. I have seen components from a competition engine using vegetable oil which have been left lying around in a slightly damp atmosphere for years without showing the usual signs of rust which turn up on similar ferrous components from an engine using mineral oil. The big difficulty is cleaning off the vegetable oil before filling the engine withmineral oil for normal use. It is probably best to turn the engine over a minimum of two revolutions reasonably regularly, if you can spin it with a starter motor even better.

[A G Wood]

I've mentioned this before, I think, but back in the days of short blocks supplied by big engine rebuilding concerns there was a product they ran through the lubrication system as a last step before packaging after they bench 'motored' the short block (with its lubrication system externally pressurised)  to do a final check on the cylinder bore lube jet orientation, gallery plug leakage, excessive oil clearances etc. It went in as an approximately SAE15 but 'hardened' to a greasy film and acted as a long term preservative on all the internal parts. Like a slightly thinner consistency cosmoline I guess. The recommendation was to just wipe off any excess when fitting the short block as the product would disperse in the running in oil with no ill effect. I've also heard of it being put in the sump of an complete engine (after the actual oil was drained) and the engine being idled for a few minutes before the engine was put into storage.  I want to say it was Shell 'Ensis', but I'm not 100% sure that was the correct name.
There's at least one automotive machinist contributor on here, I'm sure they'll be able to name the product?

[Tony Press]

For various rust preventives google Mobil Mobilarma Series and Shell Ensis Fluids.

Lots to choose from 

[JonE]

thankyou all. So can normal OIL perhaps result in the dark brown film I've been cleaning off pistons and rings... or could it be fuel used as cleaner? (I'm now wondering quite what the characteristics of diesel, which I'm using for cleaning, are as a light oil)
The engine wouldn't have been run - think likely a first assembly.

[Dave Mann]

    When we supplied diesel engines of up to 18000 BHP all the injectors, crankcase doors and cambox doors were removed and the whole of the engine internals were sprayed with Shell Ensis preservation oil prior to shipment. This gave up to 6 months protection, if the engine was to stand for any longer we repeated the process. This oil was compatible with the engine oil and didn't require cleaning off prior to putting into service.