So I was going through some oil stuff and found this website that can calculate approximate oil viscosity vs temperature based on its viscosity index by putting in the 40 degree and 100 degree cSt value. What I find useful is how I can determine which oil is better based on the temp range that I’m seeing. As you can see there is a difference between the OEM and Mobil 1 0W-20 oils, as well as Mobil 1 and Castrol Syntec 0W-30. Looking at this graph and knowing that the engine is spec'd to run a viscosity of ~7 cSt @ 100C, I think I’m going to reconsider my oil choice, as I’m currently running the Castrol Syntec 0W-30, which may be too thick for my use. Considering that I can now track my oil temp, I can make a better judgement of what to use. My steady state temp in 12C weather was 95-100C with NO cooler and up to 110C with a couple of WOT pulls. So considering that I may drop down Mobil 1 0W-30 @ 110-120 will be the ideal viscosity. Castrol Syntec 0W-30 appears to be too thick, which is what some threads have mentioned, but in saying that the OEM is SPEC’d for 90-100C ONLY and will be too thin at higher temps!!
Mobil 1 0W-30: facts
http://www.mobiloil.com/USA-English/..._1_0W-30.aspx#
Mobil 1 0W-20: facts
http://www.mobiloil.com/USA-English/..._1_0W-20.aspx#
Castrol Syntec SPT 0W-30 German Formula:
http://msdspds.castrol.com/bpglis/FusionPDS.nsf/Files/1CD14DD79D0B77DD802579D10048C4F1/$File/BPXE-8SYFN5.pdf
Subaru BRZ OEM 0W-20
http://www.ft86club.com/forums/showthread.php?t=13286
So I just wanted to post this so people that unfamiliar with oil can make a better guess of what is good based on the their use, personally for me it was a bit difficult to accept OEM oil as being SAFE for the engine when pushing it and this graph confirms those fears. Cheers and good luck.
Here is a link to the website:
http://www.widman.biz/English/Calculators/Graph.html