Originally Posted By: WillB
Going to start stocking up on 75W90 for the different on my truck, my two choices are RP 75W90 or Amsoil 75W90.
Which would you chose? Why is RP priced higher than Amsoil?
Well - this is just like any other "
What's the best synthetic my money can buy?" thread ....
Typical of most folks, you're going about this booty-backwards. Don't pick a fluid and then try to cram it into your use. Rather, analyze your use, and then see what fluids will meet your needs. Because there is a HUGE difference between wants and needs. I would even recommend getting some UOAs if you really want to tailor your lube selection to a specific application.
Now - if you just "want" a syn, and a very expensive one, to make yourself feel better, then stop reading this post and just go do whatever makes you feel good.
If you'd rather make an educated decision, then determine your OCI plan and work from there. Get a couple UOAs and establish a baseline of performance; understand what is and is not working, so that you have a reasonable interpretive position. Syns can offer some good options if OCI extension is your goal. But if you're not going there, then conventional lubes can be every bit as decent at protecting your diffs for a lot less money.
Think I'm wrong? Look this over ...
http://p-r-i.org/other-programs/automotive-qpl/lubricant/
open the "current QPL listing" and browse all the approved lubes. These all meet SAE J-2360, which is a very hardy and robust standard not just about what's in the bottle, but how the fluid actually performs in terms of wear control, foaming, vis retention, etc. It's based on a MILspec process. And if you look closely, you'll see that there are some good dino gear lube choices that meet the very same specs as many popular syns!
Do you "need" a syn? Can't tell you for sure; that would depend upon your OCI plan. Do you "want" one? Sounds like "yes" to me.
But if you're only satisfying a "want" here and not a "need", then just buy whatever tickles your fancy. When a "want" is the itch you need to scratch, then just pick something that makes you feel good, because that's about all it's good for.