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For whatever reason the Europeans are convinced that heavy weight oils are better. I do not understand this from an engineering perspective, but I do understand it from a "we've always done it this way" perspective. 40w oil requires more horsepower to pump, makes the engine run hotter, and doesn't have the ideal 10 cSt viscosity until the engine is running hotter than any street duty could achieve. If you look at viscosity curves and see what they actually deliver, you'll be pretty quick to say any (0-5-10)W-30 oil will be best for my daily driver because I don't see oil temps over 220F unless I'm really hammering the car. The difference in viscosity between 30w, 40w, and 50w at 250F is tiny, and if your engine is that tightly wound, you shouldn't be driving it on the street.
"Logic" does NOT indicate a more viscous oil will provide more protection, and in fact, it will only provide more hydrodynamic drag in the bearings (making them run hotter) and more frictional losses in the pistons reducing horsepower. AMHIK!
Why do you think back in the days of "qualifying engines" in NASCAR they ran 0 weight oil without cooling systems? MOST POSSIBLE POWER with least drag from viscosity. And you can bet the bearing clearances on those engines were considerably tighter than the "race engine" they put in to run the actual race.
I know for sure that in the UAE, lexus puts 40W due to high summer heat 40c-50c . I don't think europe countries reach those high temps.
This photo is from the GLOBAL factory service manual rm0375e . So i think the operating conditions need to be met in order to choose the correct viscosity
While the USA factory service manual rm1480u shows less options .. So maybe US regulation plays a factor here ?
Also this is from European/Global Owners Manual OM50G06E
For whatever reason the Europeans are convinced that heavy weight oils are better. I do not understand this from an engineering perspective, but I do understand it from a "we've always done it this way" perspective. 40w oil requires more horsepower to pump, makes the engine run hotter, and doesn't have the ideal 10 cSt viscosity until the engine is running hotter than any street duty could achieve. If you look at viscosity curves and see what they actually deliver, you'll be pretty quick to say any (0-5-10)W-30 oil will be best for my daily driver because I don't see oil temps over 220F unless I'm really hammering the car. The difference in viscosity between 30w, 40w, and 50w at 250F is tiny, and if your engine is that tightly wound, you shouldn't be driving it on the street.
"Logic" does NOT indicate a more viscous oil will provide more protection, and in fact, it will only provide more hydrodynamic drag in the bearings (making them run hotter) and more frictional losses in the pistons reducing horsepower. AMHIK!
Why do you think back in the days of "qualifying engines" in NASCAR they ran 0 weight oil without cooling systems? MOST POSSIBLE POWER with least drag from viscosity. And you can bet the bearing clearances on those engines were considerably tighter than the "race engine" they put in to run the actual race.
My most expensive custom engine uses 30 weight for the reasons you and I have been saying....a 40 is not needed on the street unless you have some insane specific output/highly loaded parts and even then it's moot if you have enough flow and an individual oil that can withstand the loads you subject it to. If you have a closer tolerances oil it is actually MORE tolerant of thinner oils and they will cool it better as well due to increased flow.
Last edited by DaveGS4; 01-09-23 at 02:02 PM.
Reason: Sarcastic comment not needed. I asked to take conflict to pm
Ugh, just realized it got a couple of minor door dings while spending a week at the dealer. I've avoiding parking next to other cars for 4.5 years and it ends up getting door dings at the #$%^ dealer. Argh.
01-08-23, 11:09 PM
