Thread: Poor Mileage?
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Old 02-05-2002, 04:02 AM   #10
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Member#: 14141
Join Date: Jan 2002
Location: [email protected] @ 5800 ft on 13T
2002 Impreza WRX

Default winter gas and oxygenated gas

There are actually two issues with so called winter gas.

First in the cold months of the year, they increase the volatility of the gas ( use lower boiling point blend ) that vaporizes better during cold starts. This makes it easier to start your car when it is cold, and causes a lot of people to have vapor lock problems on the first hot day in the spring before they switch back to summer blend.

Second in large areas of the country to control emissions, they add either alcohol or MTBE to the gas blend to increase its oxygen content to reduce carbon monoxide emissions. Alcohol has a lower energy pound for pound so it takes slightly more fuel to do the same work. So gas milage should drop _slightly_ during the winter.

That said, here in Colorado, (home of oxygenated fuels and cold weather blends ) I regularly get 24 mpg in general driving mostly short trips, and I don't baby the car. During break in I got 31 mpg on a long highway cruise running a lot in 5th gear.

You definately need at least 91 octane in the WRX for good performance, and higher if you can get it. If you are running a low octane fuel you could be killing your gas milage if the ECU is backing off timing to prevent detonation.

The other possibilities are things like a bad ignition coil, or fouled spark plug.

Do you have a lot of crap in the car. It only takes a couple hundred pounds of extra weight to really kill your gas milage. Are you spending a lot of time in lower gears than normal due to slow moving traffic on snowy roads ? Are you letting the engine idle for long periods to warm up in cold weather ?

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