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There's a gas station in my town that sells 100% pure gas. But the highest octane it goes up to is 90. I'm wondering what's better for my MDX:

- 90 Octane 100% pure gas

or

- 93 Octane of the gas mixture most stations sell.
 

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For what it's worth, Acura would have you go with the 93 octane. The manual for the 2nd gen advises that you should use gasoline with a pump octane of 91 or higher. It says that if that grade is unavailable you may temporarily substitute 87+.

I would also run the 93, myself.

When you say "pure gas" do you mean "ethanol free"?

Ethanol is hydroscopic, which means it absorbs water. Consequently, gasoline with Ethanol "goes bad" more quickly than gasoline without ethanol. As long as you're driving your vehicle regularly, this is not a problem. If you need to fill up your tank every few weeks, for example, then you're fine. If the vehicle will be sitting for more than a couple weeks, then you can add some Sta-bil 360 and it will keep the fuel in decent shape for up to a year.

The EPA approves gasoline with ethanol content of up to 15% by volume (E15) in model year 2001 and newer passenger cars, light trucks, and medium-duty vehicles. E10 fuel can be used in even older vehicles.
 

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One good thing about ethanol is it acts like a solvent to help keep fuel components near the engine cleaner compared to pure gas. Us old school shade tree mechanics remember having to spray the carburetors to clean the tarnish from gas (back in the leaded gas days).

I can only find 90 octane when I visit the in-laws in the eastern part of NM near the TX border. I don't know if the gas is an ethanol mix or 100% gas? My TSX, RDX, and MDX run fine with that one tank with no difference in mpgs; but, it is just level ground with cruise control set between 70-80 mph for 3 1/2 hours. I usually fill up with Sam's or Costco 91 octane ethanol mix gas depending on which gas line is shorter. I think I rather go with top tier gas with detergents to keep everything clean with ethanol compared to pure gas without.
 
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