Base oil viscosity of multi grade oil ?

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Hi

Do Oil companies use a base oil (synthetic) with the same viscosity for their multi grade oils?

What I mean is, let say Mobil sells 0W20,5W20, 0W30, 5W30,10W30, 0W40, 20W50 and etc.... Do the company use a base oil with the same viscosity and then play with the VI for their multi grade oil or they use different viscosity base oil (0Wxx,5Wxx,10Wxx or 20Wxx) and then use VI for the higher weight number ?
 
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Typically an oil company will have several base oil "cuts" with different viscosity grades. These are typically sold based on SUS viscosity (100N 220N etc) for Group I and II and based on cSt@100 for Group III and synthetics (4cSt and 8cSt being the most common) although this greatly varies depending on the supplier. Depending on the grade and whether it is a synthetic, synthetic blend or conventional fluid they will create a mixture and strategically use the viscosity modifiers (PPD's and VII's) to meet the target viscosity at the best price.

Also complicating the issue is what specification claims they want to make with their product. In order to make API claims for example the formula has to pass expensive engine sequence testing. To reduce cost the API allows a certain level of base oil interchange where tests do not have to be repeated for a new base oil as long as certain guidelines are adhered to. The same is true of OEM specs like Dexos1 although the base oil interchange rules are usually much more restrictive with OEM's.

Often the final blend of base oils and viscosity modifiers comes down to a combination of what the blender can buy most cost effectively and what their additive supplier partner (who is probably the one who ran the engine tests) can support with the program that was developed for their specific DI choice.
 
Thanks for the info. So in another words, two bottles of engine oil, same brand and same grade, could both have different mixture of base oil and VII. Is it exact ?
 
IF the bottles have the same batch number on them they have the same mixture.

A different blended batch could have a slightly different mixture.
 
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