That is the question. I've got an Olds Aurora 4.0L V8 Northstar that recommends 10w-30 but can use 5w-30 below 20F. Oil pressure is quite low in this engine at idle, about 11psi. At 1000RPMs it's well over 20psi. The spec goes down to 5psi at idle as well as some reading at a set higher RPM, both of which I well surpass. This car is mostly highway driven about 20K miles/year. I use Wix oil filters. What oil would you recommend in this car? My options are:
1. Amsoil 10w-30
2. Amsoil 10w-40
3. M1 0w-40
4. Rotella T Synthetic 5w-40
5. GC 0w-30 (is this too thin since 5w-30 only
below 20F in owner's manual?)
6. M1 T&SUV (if it ever comes out here!)