How to flush out Castrol R40?

Hi Barry, The oil can turn into a jelly if mixed with mineral so its not recommended. I think I would stick with R till the next rebuild.

Hi Barry

Castrol R is a vegetable based oil that only really dissolves in what are called 'polar solvents' like ethanol, acetone, or a good one for washing it off is cellulose thinners. It is very reluctant to dissolve in petrol, which used to be a non-polar solvent, but is now a more vicious a solvent when it contains ethanol. It is equally reluctant to dissolve or mix with non-polar, hydrocarbon oils.

If you were to put a hydrocarbon, mineral oil in the engine and run it, it would probably push most of the vegetable oil out of the way and do its normal job of lubrication. But there might be a problem somewhere with a blockage or dirt being washed out of a blind hole, so it is potentially risky.

There is also a mass of oil left in the oil tank after it is drained so (IMHO) this would have to be taken off and washed out with cellulose thinners.

I cannot see that there is any obvious flushing oil that will dissolve vegetable oil, do a job of lubrication for twenty minutes before draining, and then happily mix with mineral oil when that is added.

So, until it all gets stripped down, the safe answer is to stick with the Castrol R. But have people mixed the oils and got away with it, of course they have.

Norm.

With an 88 that my son bought, we drained it, ran it on 20W-50 for 20 mins, drained it and then refilled with Silkolene 40. It worked fine. My theory is that vegetable oil adhering to moving surfaces would gradually dissipate in use and be replaced by the mineral oil. It has clocked up plenty of miles since then.

A few years ago I contacted Silkolene (Fuchs Oil) on this question, John Rowland's reply is copied below. His advice is essentially to drain the old oil and replace with your choice of mineral oil. Please note that his comments apply to replacing Castorene R40 which is a modern Castor/Synthetic, not the original "gummy" Castrol R. If your engine still has the original formula Castrol R then the precautions described by previous contributors still hold. When I stripped my CS1 engine (after at least 5 years running on R40) it was remarkably clean, without any gummy varnish deposits. If you are sure that the engine contains a modern formula Castor based oil then it is probably not necessary to strip and clean before switching to mineral oil (but I am still using the Castorene R40).

Cheers, Ian McD

11/04/2012Dear Ian,It is easy to change from a modern non-deposit formingcastor/synthetic such as Castorene R40 simply by using the next oil you intend to use as a flushing oil. The old gummy 1940s castors were a different matter, but are no longer with us, fortunately. (Modern engine oils, by which I mean more or less anything reputable made after 1970, are better flushing oils than so-called 'flushing oil'!). Titan TXE 40, which would be ideal for your CS1, will mix with small amounts of Castorene R40, and remove almost all of it; if a trace remains this will create no problems. TXE 40 and the similar SAE 50 product, Hardwick 50, are widely used in vintage/early classic engines, particularly those where mains and big ends are predominantly roller-bearing.Titan TXE 40 is monograde of course, but it is very definitely NOT'straight'! It is just like a modern multigrade, except that it doesn'tdo the rapid flow after a very cold start trick, so necessary for 21stCentury plain bearing, high oil pressure engines. I have used Titan TXE40 and its predecessors since the 1970s in my 990cc Matchless MX4 twin (1934), and covered 60,000+ miles using it since the last partial rebuild. (Another one is now in progress after 30 years!)Some general background reading is attached.As for disposal of R40, it is essentially a vegetable oil, and thesynthetic addition is non-toxic and bio-degradable, so it can berecycled as burning oil. Unlike normal engine oils, it is ashless, so itdoes not leave hard zinc/calcium deposits after combustion. As far as I know, used mineral/synthetic engine oils are only recycled as low-grade fuel (e.g. for cement making), and any old stuff gets thrown in! I can't see a few parts per million of castor making much difference.Yours sincerely, John Rowland (R & D dept.)