Originally Posted By: JAG
Vegetable oil varnish is not as ideal as testing on motor oil varnish or combustion by-products but it has some similarities to the former. They are both polar, oxidized, and polymerized deposits. Molecular species distributions are different but the similarity is in the difficulty in penetrating/solubizing the substance in motor oils or base oils. Detergents and dispersants have polar parts that are attracted to deposits. Likewise with polar base oils, such as esters. PAO is the least polar of common base oils used and they are least capable of solubizing polar molecules/deposits. M1 0W-20 EP has a lot of PAO in it and apparently, the rest of the base oils and additives are not potent solubizers. As said before, Mobil 1 0W-40 was able to slowly solubize the deposit. It has a different detergent package and a higher concentration of it than M1 0W-20 EP does. It also has an amount of ester that is easily detectable in virgin oxidation tests. M1 0W-20 EP does not share that trait.
I plan to do more testing, using varnish from motor oil in one test type and in another, use a surface that I have burned gasoline on. In testing already conducted, it showed that if the motor oil varnish has not been sufficiently hardened, new motor oil that is the same as what formed the varnish could almost completely solubize the varnish and leave the steel surface free of any visible deposit when wiped with a paper towel. If the varnish is sufficiently hardened, I found nothing that could remove the deposit except for abrasives.
That last bit is consistent with what Shannow has posted about. In particular, one must note that frequent changes to eliminate the suspended contamination is necessary when trying to remove varnish, as the ability for the oil to not only remove from a surface, but retain in suspension, varnish products is quickly depleted.
And yes, PAO, as we well know, has horrific solubility, as does Group III (including GTL). POE is much better in this respect and is, as noted, polar.
I look forward to your testing with actual engine varnish and I would, FWIW, expect any plain-Jane PCMO to be relatively poor at removing varnish when compared to an oil with significant POE in it.Not sure how the well beyond SN/GF-5 spec additive package in the AMSOIL products plays into things here, but that's worth noting as well.
Would also like to, if possible, see how Castrol's 0w-40 compares. We know it has a good slug of PAO in it, so it would be interesting to compare it to your typical SN EC product.