Quote:
Originally Posted by Adrian E
That's where the 5w40 recommendation comes from for grade, as opposed to spec.
Ref the point earlier about 0w oils - whatever the potential benefits they might offer, you need it to stay in the engine. Older engines don't appreciate low viscosity oils particularly, even for cold start. If they're not designed for them you tend to find your oil consumption/loss goes up to no real benefit.
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It will stay in the engine, all engines need to have the oil at operating viscosity for minimal wear. No engine 'likes' to be started with oil 10 times its ideal viscosity, its a myth.
As you can see from the Castrol website the 0w30 has slightly higher 100C viscosity than the 5W30, so the 0W does not refer to viscosity at operating temp.
0W oil is always going to be better for the engine, it carries higher quality additives to achieve 0W.
Ideally, the engine should have the oil at around 12mm2/s at start up.
You were probably thinking of mineral oils, synthetic oils are different:
"a multigrade mineral oil like a 15W-40 is basically a 15 weight oil with additives to ‘thicken’ it and under extreme conditions, the additives can shear’ and collapse so your ‘behaves like a hot 40′ oil starts to behave like a hot 15…far too thin for the engine….(bang!) whereas a 0w-40 synthetic starts as a straight 40 and has additives to make it thinner when cold, so under extreme high temperature provocation when the additive package fails (at a much higher temperature point anyway) it behaves like a 40 weight, which is what the engine is designed to use anyway"