Poor fuel economy even using 98
Poor fuel economy can be the result of a bunch of factors, but my first suspect would be a cooling system thermostat that is stuck in the open position. If replacing the thermostat doesn’t help, then you might want to consider whether you are simply doing mostly short-trip local drives, and/or whether you are carrying too much junk in the trunk, and/or whether the tires are underinflated or are of the high rolling-resistance variety.
But… you didn’t mention whether the CEL is lit up.
Is it?
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Since you told us NOTHING about your vehicle except it being an 07 Ford Focus, I’ll need to pull out my crystal ball… It says…try again later when you post more information about your car…
Is the check engine light on? How many miles on it? What engine? What transmission? Does the car warm up quickly? Does it warm up at all? Did his happen recently? Did you just buy the car?
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How does the Miles per Gallon compare to what the vehicle is rated at ? How are you checking the mpg ?
Is this another one of those vague ’ Ask Someone posts ?
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Is all of your scheduled maintenance up-to-date?
Where are you getting 98?
Could be alignment / transmission issue / bad driving habits / valve timing issue / wrong oild viscosity / knock sensor fault / spark advance disabled / oxygen sensor issue. Maybe even a faulty ground causing incorrect sensor readings.
That was my question too. Where I highest is 93 octane.
Is there a low octane AVgas?
98 octane, are you in Europe??
I concur w/ @VDCdriver above, best guess with limited info, engine coolant isn’t reaching proper warm-engine temperature. Do you have a coolant temperature gauge on the dash? If so, what does it read after 15 minutes of driving?
There’s a big part of the planet that’s not the USA, believe it or not.
Oh right 95 RON = 91 octane. I should be ashamed!
Calexico, California. Watch out for those bad drivers on state route 98.
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Believe it or not, the higher the octane, the lower the energy in the gasoline.