Originally Posted By: FastSUV
Originally Posted By: ekpolk
That's a trickier question than it appears. The pivot point is what do we mean by "bad". May sound simple, but it's really not, at least in this context. Is "bad" a spec-oil that has a skimpy add pack? Is bad a true non-spec oil like an SA used in an SM car? I think we could probably all agree that would be bad...
My opinion is that for "normal" contemporary vehicles, if it meets the SM standard, it's serviceable (good or bad up to you...). If you have a car that needs a strong EP and/or AW additives (like everyone's favorite ZDDP), things get trickier. And so on.
Need a better definition of "bad".
If you did an oil test and took say 10 different dino oils of the same weight and ran them in a chevy 350 changed every 3-5k for 250k miles for the same operating conditions and then disassymbled the motors and compared the wear, cleanliness, etc. Then would their be one oil that SUBSATNTIALLY stood out as the poorest performer with no debate about it. And then it could be said that all the other oils did a "good" job protecting the motor but OIL #10 is a "bad" oil and don't use that in your car.
does that help a little?
No, unfortunately not very much. The point I'm trying to make is that, while there certainly will be variation in performance between different oils, it's still very hard to isolate what such variation means. For example, if the test engine you choose to use is a flat tappet design, as it appears you've chosen, then among the many variables in oil performance, perhaps the characteristics of the EP and AW additives become the critical controlling factors. If you choose another engine for your test, say an early Toyota 1MZ V-6 that had the unfortunate habit of roasting its oil to death, but no EP issues in the valvetrain, then perhaps heat tolerance or oxidation performance becomes the critical variable that will define what's good and what's "bad".
I'm not simply "playing dumb" on this question. I'm just trying to point out that when you're looking at a product like motor oil, that may vary from a similar product in dozens of different ways, using overbroad labels like "good" and "bad" doesn't help much, unless we do more to define what we mean by good or bad, for a given situation.
Ironically, the standards (SAE, ILSAC, etc), which have been so helpful and positive overall, may actually help to mask and obscure real differences between lube products. For most apps, you can safely grab whatever oil carries the right approvals. Hey, if it says SM, and your car calls for it, you're very probably totally safe grabbing any SM that suits you. But if you want to parse it out more, you'll have to dig deeper to find the individual data points about the oil that you find important for your application.