Quote:
Originally Posted by 335iAW
Wait, so I can put 89 octane in my 335i?
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Yes, 89 is fine.
The fuel door states 89 is the minimum.
The manual indicates when using "the engine may produce knocking sounds when starting at high outside temperatures. This has no effect on the engine life."
That is, the engine may make sound briefly under this limited circumstance, but it is not harmful.
Many here speculate that since BMW states it used 91 octane when testing for maximum horsepower that somehow the engine will be damaged or compromised by 89. Thus, they argue one should use 91 or better for maximum engine life.
This is nonsense. While 91 will do no harm, there is nothing to indicate it is safer or in any way "better" for the engine. One may get a bit more power given BMW's call-out of 91 along with the power specifications, but we do not actually know.
Bottom line: 89 is fine, will definitely not hurt. 91 is fine, will definitely not hurt, may potentially provide a tad bit more maximum power. If emotionally 91 makes you feel better, use it. It is not much more on an annual basis.