OK gang, since my oil knowledge is still somewhat limited even though I hang out here often, I thought I'd ask your clarification on this brief exchange I had on a Nissan newsgroup re: polymers and synthetics (quoted below). My question is still the same: if synthetics in fact do not use polymers to achieve wide viscosity ratings, then what do they use? And is it still as harmful as polymers so that you'd still prefer a narrower spread synthetic (say 10w-30) rather than a wider one (say 0w-30)? Thanks!
wrote in message >news:[email protected] >> The other great benefit of synthetic oil: dino oils use polymer >> viscosity index improvers to get wide viscosity (5w30) ratings. These >> polymer VI improvers break down leaving sludge, gum and varnish. >> Synthetics don't need these so they last much longer in service >> without gumming engines. To that, I replied: Why would synthetics not need polymers to achieve the viscosity spread? How do they accomplish it then? I thought both dino and synths use them. And to that he replied: Don't fully understand the chemistry, but here goes: Long chain polymer molecules added to oils are tightly coiled at lower temps and uncoil as it's temperature rises. This uncoiling thickens the oil as it heats and counteracts the base oil stock's thinning as it heats. That keeps it relatively thick at the higher temperature. It stands to reason that the wider the viscosity range of an oil, the greater the relative quantity of polymers added. Synthetic oil is much more stable so it simply doesn't thin as temperature rises so the addition of polymers is unecessary. Better synthetic oils don't have any added polymers at all.