It used to be (maybe still is) that General Motors specifically warned not to use 10-40 or any other oil that had a 30 point spread or more as they contained so much viscosity improvers, that they became undesireable oils for engines. Is that still the case? Seems there is a rash of newer oils with 5-40 and 5-50 weights. Have they found a way around using viscosity improvers in the quantity they used to. It does seem though that the "wide spread" viscosity numbered oils are all or mostly synthetic. So is a 5-50 oil safe to use without fear of breakdown?
viscosity improvers
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i'm pretty sure all 5W-50, 15W-50, and 5W-40 oils are synthetics... are they not? i dont think i've seen a conventional oil in those grades.
i know of plenty of people who run 5W-40 in their BMW engines. it all depends on the engine, i guess.
25 years ago Shell had a conventional 15w50 oil, but that was then, now it does seem they are all synthetics. Is there a way to determine how much viscosity improver is in an oil, and compare it to what GM says is to much?
Try a centrifuge.
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=1;t=015771
Some numbers for current formulas, but don't know the number for 10w-40 from 1990.
Some numbers for current formulas, but don't know the number for 10w-40 from 1990.
I think Castrol 5w50 is a blend of grpIII and IV. Since they started blending III, IV and V there are some pretty good wide spread oils out there.
ya, i think high-spread oils are much better these days.
I thought Terry's analysis of Green GC showed no polymeric thickeners, yet its VI is around 165. If true, it still is a rare thing among oils, so your point would still a good one in general.
IIRC, synthetic like Amsoil don't use VI improvers in their oil. They achieve "stretch" from the nature of the oil. I remember seeing a video about VI and how it bound the oil molecules together and eventually was beatten to death in the pounding of the journals. That was always one reason I liked synthetic over regular oil, was that it attained the range that was desirable, but without any of the Viscosity Improvers.
Several oil companies had motorcycle oil, 20W-50 that was all dino/conventinal oil.
You can make a PAO/Ester, synthetic basestock blend with a VI in the 140-155 range without using any polymeric thickener. Any oil with a VI significantly higher than that is using some polymer.
A group III based 5w30 will have about the same percentage of polymer as a PAO based 5w-40. The VI's of the PAO basestocks are significantly higher than for Group III's. Hence it takes more polymer to make a given SAE grade using Group III stocks; compared to a PAO - this is why they tend to shear more in service.
GM sticks with 5w30 and 10w30 since they contain the least amount of VI modifier. An SAE 5w-20 may contain even less; I think that's why that grade tends to be pretty shear stable.
TS
A group III based 5w30 will have about the same percentage of polymer as a PAO based 5w-40. The VI's of the PAO basestocks are significantly higher than for Group III's. Hence it takes more polymer to make a given SAE grade using Group III stocks; compared to a PAO - this is why they tend to shear more in service.
GM sticks with 5w30 and 10w30 since they contain the least amount of VI modifier. An SAE 5w-20 may contain even less; I think that's why that grade tends to be pretty shear stable.
TS
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