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bobstheoilguy.com
Your engine is designed to run the oil at a specific temperature (usually 212F) all the way from Alaska to Florida. This maximizes efficiency, reduces emissions and maximizes lubrication protection. Running a 40 weight or higher in the Summer isn't necessary for a street driven vehicle but if you're going to be running it at the track, which will raise your oil temperature above 240F, then you can step up your viscosity to a 30 or a 40 weight.
Knowing what viscosity oil to put in the car depends on 2 things, temperature and pressure. You want to run the thinnest oil your engine is designed to run to maintain the cSt (centistoke) at a given temperature and proper pressure at a given RPM.
Example:
1: If my street car says 5w-30, that means it's designed to run on a 30 weight oil at 212F (a 30 oil at 212 is 10cSt). So if I'm raising the temperature of my oil to 260F then the 30 weight oil is now at 5-6 cSt (too low for design of the engine and could also lower pressure) and thus I need to consider running a heavier oil like a 40 weight.
2: If my oil pressure is below the 10/1000 rule (10 psi for every 1000 rpms) then I need to consider a thicker oil for track-day purposes to increase pressure at racing temperatures.
I personally will not be running a thicker oil than the 0w-20 unless I start playing with this at the track, which I may not do as I already have a race car for that. I will just plan on buying a very high quality 0w-20 like Amsoil European formula or Joe Gibbs street oils.
(Daddy likes his Zinc content).
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