[Region Warrior]

of course oils are better now. not sure if GM's archives go back far enough(80's), or shortly after 10w40 came out. i will try to find it. an independent company tested all the major brand motor oils for GM, they probly still do this. most all multi-vis oils pasted thier minumum tests, except 10w40(none passed). it also stated the wider multi-vis oils broke down quicker then straight wieghts, but not really a concern if regular change intervals were followed. GM did not publicize this to the public, it was a service bullitin, recommending not to use 10w40 in any gasoline vehicles and change oil earlier if multi-vis oils where used. i have read elsewere on the subject, maybe even here. now for my personal experience, i have helped a race engine builder tear down/build engines on & off for 20 yrs. the straight wieght engines "most" always have the least amount of wear. he always recommends 30w & or synthetic blends after break-in.