Originally Posted by zoom44

the mandate from the epa is that the company must recommend the oil it uses in MPG and emissions testing. most companies are switching to 5w20s because they have found they get better mpg ratings with them. that helps them stay within the CAFE standards.

this has all been said here before by me and others

Originally Posted by zoom44 on 12-21-2004

why is 5w20 recommened in the USA but not in other countries? simple answer- CAFE which stands for corporate average fuel economy. this is a US federal standard that each auto maker has to meet a certain product line wide avg mpg. Ford companies as well others have started shifting to thinner oils because they get better fuel economy during the EPA testing than heavier oils. now the answer to why 5w20 and dino oil is recommended and why does every Mazda employee stick to the company line. because whatever oil that is used when the car is undergoing epa testing HAS to be USED AND RECOMMENED FOR USE TO THE CONSUMER. they cant use one oil for testing and then have you use another. its against epa regs. That is the main reason they keep saying dino only. the other reason is that they just do not want to spend the time , money and personnell resources to test the efficacy of synthetic oils. the dino works fine so why bother? its a bottom line bean counter decision. (Source)

Originally Posted by ZoomZoomH

I should be up for my 3rd UOA soon (using Castrol GTX 5w-20)

I will post results once I have it done :D