Conventional in bmw n54 for 60k kms

[OVERKILL]

I have a 5L jug of that I bought 4 months ago. The pds shows A3/B4, but there’s no mention of it on the container, just api/sp and no mention of it being a synthetic blend.
On sale with stacked savings it worked out to about $20 USD.
If it’s truly a3/b4 I’ll use in my lawn tractors which both have the 726cc Kawasaki engine.

Yeah, and there are some exclusions for non-ILSAC grades in API SP, such as:
- TEOST 33C high temperature deposit test
- Emulsion Retention
- Gelation Index
- Sequence IIIHB - Phosphorous retention
- Sequence VIE (this one isn't quite clear, because they do list 10W-30 and above, but it's also noted with the footnote "not required for non-ILSAC grades")

 

[userfriendly]

Maybe because 10w30, 10w40 and 20w50 are not considered resource conserving (fuel economy standards) none are recommended grades in anything of late that I can think of and none of those grades carry new car warranty approvals or licenses.
There might be some military specifications. I have at least a 5L jug of each in my stash.
Now I hafta go look see.
Would a SP additive package at 125% treat rate get me A3/B4-SP?
Lastly, can those grades of GTX be mixed without running into additive chemistry incompatibility?

 

[FCD]

I don't think there would be any issues with mixing them.
To be honest i have never really liked Castrol, from my personal butt dyno experience it has just made the engines in my cars sound more rough and unpleasant, just my subjective experience.
But my experience so far with this new GTX SP Syn Blend 20W-50 in my 75 Capri has surprised me, it seems to run pretty quiet and smooth, though maybe not as smooth or quiet as Motul 4100 15W-50.
Completely unscientific and subjective review but that's my 2c