Arthur wrote on 01/31/08 at 21:39:50:KwakNut, I've been told that forcing oil through the stress of bearing surfaces and other moving parts in an engine, causes it to break down on a molecular level. It is supposed to become less 'slippery', after being subjected to this trauma due to it's molecules being re-arranged. This was given as the reason why re-cycled oil will never lubricate as well as virgin stock. Apparently it is not possible to re-arrange the molecules into their original format. Is there any truth to this?
Mostly, yes.
Oils break down mostly through exposure to temperature (mainly oxidation) or physical sheer. When the molecules are ‘broken’ under physical loads, they literally become different substances. For example, of you break a pair of joined carbon atoms off the oil molecule string, you get a molecule of ethane gas produced – that just bubbles off and disappears through the vent system.
The blackness that forms in your oil is just suspended carbon – single carbon atoms in a graphite lattice structure – which are produced both from oil breakdown and, mostly, combustion by-product (ie, burned fuel residue washed off the bores by your oil). The detergents in the oil stop this carbon from sticking to steel and aluminium, then the dispersants polarise it and make small bits of carbon repel from each other – in that way the carbon particles are kept smaller than the oil film thickness and should not contribute to wear.
Others bits of oil molecule are boken off and in effect become lighter strains of petroleum product, but in very, very small quantities.
Those molecules can’t be rearranged or mended, but through filtering and re-distilling the recycled oil stock, they can be mostly eliminated, so recycled oil is useable. Quite happy to put it in my lawnmower or an old high mileage dog of a car – but it wouldn’t come within yards of my bike’s sump!