As seen on another board. Enjoy -
If an engine or any other steel component for that matter, has been assembled with or previously been in contact with a mineral oil then you cannot switch to a synthetic or semi-synthetic oil anyway and vice versa
synthetic and mineral bases do not mix and produce carbon particles in the oil that act like a lapping paste and damage the bearing surfaces of the crank and camshaft
it is possible to change the lubrication type IF it is completely removed at a chemical level. Just wiping it off is not sufficient because steel is porous and absorbs the lubricant at granular level. A chemical degreaser can be used but then the degreaser needs to be removed by heating before the new lubricant is applied or else it will be 'degreased' too
it is nigh on impossible to do this to an engine unless it is stripped to bare components and each surface is degreased
the biggest problem is heating up a hardened surface, like a big end journal, as it will start to temper and no longer be a 'journal'
so the upshot of all that is, if your engine has synthetic oil fitted as factory spec, then stick to that. If you drive old **** that has mineral oil as it's spec, then stick to that
DO NEVER MIX
because it won't improve the wear capabilities of your engine
it will make it worse
and further explained as -
i don't doubt that many people have done it and 'got away with it' but strictly speaking it is not possible and they will have experienced accelerated wear but not attributed it to the oil base type
synthetic and mineral dissimilar base reaction is even more pronouced if anti-fretting agents like copper are also in the lubricant - that really does react if 'mixed'
(Tribologist mode)
if a steel component has a mineral lubricant applied then it effectively forms a barrier coating on the surface, when a synthetic base lubricant comes into contact with it then it cannot adhere (and protect) the steel surface as the mineral lubricant is blocking it. The synthetic lubricant is then not the lubricant anyway but just the thin coating of mineral is doing all the work and vice versa
therefore if you have an engine with mineral base oil in it and you drain it off and put synthetic base oil in instead, the synthetic is doing absolutely nothing to lubricate the components and is merely sloshing around - it is the thin coating of mineral that is left that is the lubricant - this cannot last long
the reaction behind dissimilar bases causes carbon (fossilised) particles in the mineral oil to migrate out of it and they cannot mix with/dissolve into the synthetic base oil. They are suspended in the synthetic base and the oil becomes effectively a 'lapping paste'
Comments welcome...
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