either Castrol or Mobil1 full synthetic 5w-30, whichever is cheaper at the time it is needed.

Rotella Synth. I learned about it on M.net (where else?) and have been VERY happy with it!

Just picked up some Rotella T6 5w40

Yes:)

I use this:

https://www.miataforumz.com/attachme...ine=1320337204

Im now running Shell Rotela T6 10w-40
https://www.miataforumz.com/attachme...ine=1333819076

i thought that stuff was 5w40? they change it up, or this a different weight version now?

M1 0w-40 for the last few changes with WIX filters. When I was turbo I was running AMSOIL SS 10w30

Mobil1 OW-40. Because I use it in all my vehicles so I only have one oil to buy; the others do need 0W-xx, the Miata doesn't because it's never run in winter.

I'll dispense with the anecdotal evidence and go with some science; as a summer oil, it meets API for multigrade xW-40, straight 40, 50 and 60 at 212F, and meets ACEA High Temperature / High Shear test conducted at 302F (API does not require oil to meet a HTHS test but has developed a standard for it; Mobil1 meets the HTHS 302F API standard for xW-40 multigrade, and straight 40, 50 and 60 wt).

Rotella T is nice oil, they don't publish it's specifications but do publish it's ratings; it does meet the Japanese 4-stroke Motorcycle Oil standard, which implies good HTHS performance.

Right now I got Castrol Syn 10w30 in my miata, and 5-w30 syn in my 94 z71 truck, Miata seems happy with the 10-30, I use to run 10w30 in my truck but switched to 5w-30 I i noticed it is quieter on start up.