Quote:
Originally Posted by jwight
Your smart comes from the factory filled with Mobil 1 and almost everyone continues with that oil or another similar synthetic. Numerous threads on this. 
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I think it is likely that the engines come out of Japan filled with Euro-grade Nippon ENEOS Premium Hyper 5W-30 (fully synthetic, API SM, ACEA A3/B3/B4), their own product from Nippon Oil Corp. (until recently, Nippon Mitsubishi Oil Corp.)
ENEOS is available in the US in five grades, including "Enhanced Fuel-saving 5W-30" (API SM, ILSAC GF-4) and "Extended High Performance 5W-40" (API SM, ACEA A3/B3).
The ACEA A3/B3 spec refers to extended oil change capability, and the ILSAC GF-4 spec refers to fuel-saving ability - they are mutually exclusive. I am firmly in the 5K-or-6mos camp, so would choose the GF-4. The 10K crowd may choose A3/B3.
N.B., Mobil 1 0W-40 is API SM and ACEA A3/B3, but not ILSAC GF-4. Mobil 1 Extended Performance 5W-30 is API SM, ACEA A1/A5/B1/B5 and ILSAC GF-4, and as above, my choice.