Noob Fuel Question!

kannibul

Cost. There aren't any gains to be had with using 93 over 91, short of an ECU tune or Force Induction.

That said, sometimes gas stations get batches that are under or over rated.

There are stickers on the pumps here in the US (not sure in Canada) that show a test date, and a +/- rating on 87 and 91 octane fuels. I've seen some test 87 octane as high as +5 (meaning it's 92 octane that day, that month), and as low as -2. 91, I'm just now paying attention do since the Z. I've seen a few say +2, others 0. Here, the gas is tested annually, so...they could go cheap and put crap gas in the tanks after their testing. Depends on the owner...the bigger corporate-owned places tend to be better (also go to the busy stations, they cycle fuels faster!), but the one-off ma-n-pa no-brand / small chain gas stations are the worst about it. They tend to get whatever gas they can get the cheapest when they need it most.

They don't test 89 octane here because it's really just 91 and 87 mixed in the pump.

Lastly, if you see the fuel truck at a gas station, don't get gas there that day. Sure it's the "freshest" and least likely to have any collected moisture in the fuel, but, all that fuel dumping into their storage tanks, stirs up sediment and out the pumps it goes into your tank, into your filter. Wait a day...