Blended Oil Cocktail, simple Q for smarter people

[JFP in PA]

Originally Posted by BrokenLinkage

Ok, so I've started doing my own oil changes. My preference, after much review of the info here and elsewhere, is for Castrol Syntec 5w40, which is rare as hen's teeth around here.
Mobil 1 in 0w40 (Porsche approved) and 10w40high mileage is readily available and relatively cheap. If I blend the M1 0w40 and 10w40hm will this result in an appropriate 5w40 weight oil for my '01S?
Or suck it up, pay the extra, and order the Castrol in the correct weight?
Thanks in advance for the education.

Maybe. Different oil manufacturer's often start with completely different blend stock bases, then use their own additive packages to put the oil into the weight characteristics they want. So blending two different brands of oil could easily take you just about anywhere viscosity wise.

You would be vastly better off not playing "mad chemist" and buying the correct oil. Either go for the Castrol 5W-40, or better yet the Joe Gibbs DT 40.

[Jamesp]

Originally Posted by JFP in PA

Maybe. Different oil manufacturer's often start with completely different blend stock bases, then use their own additive packages to put the oil into the weight characteristics they want. So blending two different brands of oil could easily take you just about anywhere viscosity wise.

You would be vastly better off not playing "mad chemist" and buying the correct oil. Either go for the Castrol 5W-40, or better yet the Joe Gibbs DT 40.

+1 based on memories of a fuels and lubes class I had about 30 years ago.