duane@ucla-cs.UUCP (09/24/84)
I was suprised by a recent statement made asserting that a multi-viscosity oil got MORE viscous when cold. I assume that was a typo or perhaps someone can correct me. If I remember my fluid dynamics (doubtful), viscosity is a measure of a fluid's resistance to motion through it. The viscosity of air is much lower than water, just try running through them both. One would hope that cold weather would find the oil "thin" so that starts would be easier. I remember an article from years ago that was neither for nor against multi-viscosity oil but was against misleading advertising claims. Yes, there were additives to prevent "molecular bond breakdown". Yes, multi-viscosity oils change viscosity over a wide range of temps. No, viscosity is not a measure of an oils ability to lubricate. The article claimed that, in theory, temperatures could increase, viscosity would increase, but at some point the oil's ability to lubricate might decrease. Within reasonable temp ranges this might not happen. Bottom line - just because your oil is getting "thicker" doesn't mean it is still lubricating. Since I'm not a ChemEng or otherwise qualified, I'll stop here and ask a more qualified respondent to verify or refute my memory.
fish@ihu1g.UUCP (Bob Fishell) (09/25/84)
Almost any fluid will get more viscous with low temperature because
the molecules have less free energy then and are thus less inclined
to not be in each others' way.
Oil viscosity refers to (well I think) its characteristics at operating
temperature. Multi-viscosity oils tend to remain near their optimum
characteristics over a wider range of operating temperatures, and are
thus better suited to climactic extremes than are the single-viscosity
oils.
--
Bob Fishell
ihnp4!ihu1g!fishgino@voder.UUCP (Gino Bloch) (09/26/84)
[oil me mama!] >> Multi-viscosity oils ... are thus better suited to climactic extremes >> than are the single-viscosity oils. Where can I get this stuff? :-), really. -- Gene E. Bloch (...!nsc!voder!gino)
pnovak@ihuxm.UUCP (paul novak) (12/12/84)
a few weeks ago i posted a question to this newsgroup regarding oil viscosity: specifically why in a cold winter climate, you don't always want the lowest "W" rating. (question arose because the owner's manual for my parents' 84 pontiac parisienne (8 cylinders) recommends 10W-30, but recommends 5W-30 for my sister's 84 sunbird (4 cylinders)). i never received any replies from that question and went off trying to gather some information myself. i learned a little, thought i'd report it. i first called GM. was told 5W wasn't needed in the large engine cause it's starting system could start the car with a 10W oil, but could not answer why the 5W wasn't preferred since it should make starting easier in any car. then i called shell and mobil, who pretty much said i should use what the owner's manual said. finally i called the american petroleum industry in washington and gathered the most, but still incomplete, information. from API (this is all one person's opinion/knowledge) i learned that my premise is valid. the auto manufacturers are allegedly pushing for 5W-30 oil in all 1986 model cars. they have to get support of the oil industry and the EPA. to do this, they have to prove that 5W-30 oil is better for the engine than 10W-30. i asked the API person why it always wouldn't be better, and all he could say was that there were different additives in 10W-30 than 5W-30 oil. apparently, the EPA is involved to insure that if 5W-30 oil is used there will be sufficient engine protection in the long run to minimize pollutants. also, the oil/lubrication don't appear eager to accept the auto manufacturers test results. this may be because the oil companies think the auto manufacturers are up to something to intentionally shorten the life of a car (gee, imagine that) and that blame would eventually fall on the lubrication industry, or because 5W-30 oil is manufactured only by a few oil companies and they may be foot-dragging until all of the oil companies are ready to produce it. the personal recommendation to the person i spoke to was to use only the recommended oil weight during the warranty period, but that 5W-30 oil (or 5W-40 if your manual calls for 10W-40) would be better for your car. that's all. paul novak ihuxm!pnovak