Quote Originally Posted by Talha View Post
So I recently bought 2004 Aveo Manual 1.6L in Canada.

The car gave me 350km in a full tank (40L) on highway.

Then It gave me 280km in city with a full tank.
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I decided it needs maintenance, although the oil was relatively new, i still decided to change it.

I put Castrol Advanced Synthetic Oil in it. With a filter from FRAM and an air Filter from FRAM as well.

Used an Engine Flush liquid to clean up the engine

and put NGK platinum spark plugs in it.
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I filled up the tank with High octane 91 Gas, and It gave me 400km in a full tank in city,
I am still not satisfied with the performance as I drive a manual car a civic/corrolla/mazda3/acura gives better mileage than this car as I discussed with my friends who own these cars.

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Does someone have suggestions for me, i expect atleast 500km in a full tank, does anyone get than mileage? If you get it then how?
I do get that 500K per 40L in my 2005 manual (it's actually 32 MPG). Medium speed driving, but almost no stop-and-go or lights. Your "highway" mileage seems WAY too low. But what speeds are you usually doing? If you're travelling at very high speeds, plus lots of wind and/or hills, that might explain it a bit. Also, do you like to "wind it way up" all the time? That could be a big waste of fuel, depending on how much shifting you do. I shift at 2-3K, but never so early that the engine lugs.
"500K per tank" is ok for a rough calc, but in order to really be sure of what you're getting, you need to deal with exact numbers. Fill it up, and reset the ODO to zero. When nearly empty, fill again, record the mileage (Ks) and fuel usage, and also reset the ODO. Do this all the time, and then you have the exact KPL. And +1 to what PR said, skip the 91 and just use regular octane.