quote:
Originally posted by TooSlick:
I'd have to agree with Ken2 about the relative merits of ACEA A3 vs A5....
The primary reason for the mininum high temp/high shear viscosity of 3.5 Cp as part of the A3/B4 specifications is to prevent wear under high temp/high load conditions. An oil that is 15%-20% thinner isn't going to provide the same oil film thickness in the bearings or valvetrain under these conditions. With thinner oils I believe you do rely more on the antiwear additive chemistry.
It is true that the A3 and A5 test sequences have the same limits on wear and deposits, but you have no way of knowing with how much margin the 0w-40 passed these tests in comparison to the xw-30 formulations.
Most of the top tier OEM oil specifications in Europe are based on ACEA A3/B4 as a starting point and then add manufacturer specific tests in their own engines.
I do think that the A5 oils should be as durable as the thicker A3 formulations, but I haven't seen data that shows they provide the same level of protection for engines that aren't specifically designed to use low vis oils.
Tooslick