Octane, mpg, and fuel tank capacity questions

[whiteI30]

Hi. I drive a 98 I30. I'm trying to figure out my mpg and if I need higher octane. Inside the fuel door it says "premium fuel recommended for maximum performance". But yet my friend with a 98 Maxima told me his says regular unleaded with no mention of premium. Is there something different in the I30's engine that could benefit from higher octane fuel, as compared to the Max? We both run 87, usually Mobil or Shell, and neither one of us can hear any pinging from our engines. We've both tried higher octane but didn't notice anything different.

What is the total capacity for the fuel tank? I read online 70 liters which is 18.492 gallons. Is there a reserve tank? I'm trying to figure out my mpg. Is there a way to check in the little info box below the gauges?

[MinisterofDOOM]

There's no difference. The stickers both mean basically the same thing, though. The sticker on the I is saying that 87 is fine but higher octane will allow for more power. The case is the same with the Max. Both have the same motor, and both can compensate for knock by retarding timing, which reduces power. You are both okay running regular unleaded.

You don't need to know fuel tank capacity to calculate MPG. All you need to do is make sure you fill up completely but don't top. Then the next time you fill up, do the same, and divide the distance traveled by the amount it took to fill the tank again. There's your MPG.But, yes, 70 liters or 18.5 gallons is correct. There's no reserve tank.

[whiteI30]

thanks Minister. It never occured to me to figuring out the mpg that way, so simple. I learned something today.