BrettW
Platinum Member
I just bought Rotolla 5W40 Syn, seems to work very well, but what the heck is it really? 5W with stuff mixed in to make it thicker if needed? OK to use in a diesel? It is Ch4 rated. thanks, bw
what is 5w40 really?
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RalphVa
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I've seen Mobil 1 in 0W40. The common grades around here are 5w30 and 15w50. They can control the PAO reaction process to get the proper viscosity index and weight. I asked a guy who used to work for me (and is still working for ExxonMobil in the lube oil area) who was privy to the Mobil secrecy stuff even before the merger.
Think there are very few additives in PAO (poly alpha olefin) synthetics. Whereas, dino oils with even 10w40 vis spread would have 20% additives. One of the additives is a viscosity index improver that moves the VI from out-of-refinery level of 105 up to 140. Think most of the base dino oil is around a 15w. The VI improver moves it to the typical non-syn 10w40 level.
Ralph
Think there are very few additives in PAO (poly alpha olefin) synthetics. Whereas, dino oils with even 10w40 vis spread would have 20% additives. One of the additives is a viscosity index improver that moves the VI from out-of-refinery level of 105 up to 140. Think most of the base dino oil is around a 15w. The VI improver moves it to the typical non-syn 10w40 level.
Ralph
willfick
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slowrev
Elite Member
My understanding is that the lower number is the base viscosity and additives make it thicken up to the higher number when hot.
Could be wrong, but this is my very basic understanding of how multi weight oils work, regardless of synthetic or not.
Ben
Could be wrong, but this is my very basic understanding of how multi weight oils work, regardless of synthetic or not.
Ben
RalphVa
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Pretty true for dino oils: lower number is base and higher number is what you get with VI improvers.
For synthetics, they come out about 140-170 VI without additives. They also come out naturally low in pour or fluid point and don't need this additive. Think they probably still add some of the detergent stuff, particularly to keep diesel solids in suspension, etc. However, they won't have the VI improvers or pour point depressants that seem to be the ones that either break down and cause the oil to thin out or goop up and make it more viscous.
Ralph
For synthetics, they come out about 140-170 VI without additives. They also come out naturally low in pour or fluid point and don't need this additive. Think they probably still add some of the detergent stuff, particularly to keep diesel solids in suspension, etc. However, they won't have the VI improvers or pour point depressants that seem to be the ones that either break down and cause the oil to thin out or goop up and make it more viscous.
Ralph
slowrev
Elite Member
Ralph,
You have really confused me now ??? How is there different weights of synthetic oils if they are all 140-170VI ? Not disputing anything, just confused.
Ben
You have really confused me now ??? How is there different weights of synthetic oils if they are all 140-170VI ? Not disputing anything, just confused.
Ben
Adirondaks
Bronze Member
The weight is the viscosity of the oil. This changes with temperature. The W stands for winter. When the temprature of the oil is 0 degrees it has the same viscosity as a 5 weight oil, and at summer temp it acts as a 40 weight oil would.
Learned in tractor school 30 years ago. Go Aggies.
Learned in tractor school 30 years ago. Go Aggies.
slowrev
Elite Member
That is what I thought 5W40 would have a Viscosity of 5 at zero degreees and 40 at operating temps. Same for syn or dino.
