Originally Posted By: Clevy
Basically a 10W-30 starts life as a 10 grade oil. Then viscosity index improvers are added so that the oil with thin less when up to operating temp. The problem with that is these VII are usually polymers derived from plastics and they degrade in use and can become deposits and sludge.
No. Completely depends on the oil as to what the viscosity of the base is and the VI of the base oils used. For example there are numerous 5w-30 oils now on the market with no VII's, meaning they sure as heck aren't starting out as an SAE 5
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Thin of them like a coiled up snake. As the oil heats up the snake uncoils,maintaining the oils viscosity. In used the coils are cut(shear)and the oil starts becoming what it started out as.
That problem really no longer exists to that degree so you can discard the 10w part of the recommendation and focus more on the 30 since its the operational viscosity.
They polymers work both ways. They reduce viscosity increase as the oil cools and increase viscosity as the oil heats. So you could have an oil with a base that, at 100C, puts it in SAE 20 territory and VII it into a 10w-30. However you could also have an oil that, depending on the VI of the base oils used is very close to being a 10w-30 or is a 10w-30 right out of the gate.
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Any of today's 30 grades(not weight) will be far better than what was available when the car was built.
Yes, they most certainly are.
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In fact when the car was built the 30 grades of that era would shear and become a 20 grade,so in reality the engine was operating with a 20 grade in the sump for some of the oils interval and those engines were still legendary for their longevity.
No. While that was possibly true of some (most?) 5w-30's of that era, it wasn't necessarily the case with the 10w-30 oils which were inherently more shear stable.
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And lesson time since by the post I quoted you don't know what the w means on the oil labels. It means winter,not weight. So a 5w-30 means the oil behaves as a 5 grade does (thickness) in the winter when cold and the 30 means it behaves as a 30 grade when up to operating temp.
No.
The 5w simply denotes the oil passes the 5w CCS and MRV requirements at -30C. Which, IIRC, is 6,600cP for the CCS. It has nothing to do with the oil behaving like an SAE 5 would in the winter when cold.
The numbers before and after the "w" are measured using different testing protocols at wildly different temperatures and have no correlation with each other. The SAE 0w, 5w, 10w, 15w, 20w and 25w designations are separate from the SAE 20, 30, 40, 50 and 60 designations. Of course they all fall under SAE J300.
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Oil isn't measured in weights,they are separated by grades. Weight has just been around for so long that people haven't adopted the proper terminology and since most of us know what is being implied its accepted.
It really isn't
that wrong
There's a nice little WIKI on it:
http://en.wikipedia.org/wiki/Motor_oil
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These numbers are often referred to as the "weight" of a motor oil, and single-grade motor oils are often called "straight-weight" oils.
