Normally, my fuel light turns on right around 261 miles on the trip odometer. Lately, I've been noticing it coming on earlier and earlier, to the point where it will come on around 240. I inspected my air filter today, and it was a little dirty, but nothing to the point where it would majorly affect the fuel economy that bad.

The only thing I could think of is that I run the combo defrost (floor heat + defrost) constantly because of the fantastic chicago winter. But then again, I ran the AC during Summer and didn't notice that drastic of a difference in fuel economy.

Could it be my spark plugs doing it? That's the only thing I can think of, as I've got 28,000 miles on the stock plugs. That and my front bald tires. But seriously, wtf, mates?

 

Im in illinois too, i only have an OZ, however. And i have noticed a decrease in gas mileage for some reason. When i filled completley up in the summer, it would be 50 miles before it would go down below the F and now that number has decreased to about 30-35. No idea whats going on, might be the changed fuel chemical make up for winter. Who knows...

 

ive heard they have additives for the winter so the gas doesnt freeze..could that be the case?

it's definately not the spark plugs cause they are supposed to last as long as the car lasts..u won't even need to change them til 100k miles or so.

im suspecting something with the gas cause my friend also is noticing a decrease in his gas mileage for his mini cooper S. he says he's been driving like crazy lately, but he's been doing that for as long as i remember..

 

I believe gas freezes at -97 degrees Fahrenheit. As for the worser gas mileage, heat has nothing to do with gas mileage only AC does. Heat is from your Radiator thats why heat is not instantaneous like AC is. Your car has to heat up the coolant and water in the radiator. The gas mileage may be the spark plugs becasue on my 00 Galant the recomended change for sparks is 36000. The gas mileage may also be becasue of under inflated tires. bald tires that dont grip as well as new tires may also be an issue. More weight in the car can be anohter factor. There are so many posibilities that could be causing worser gas mileage. All i can say is trouble and shoot and keep us posted.

 

Does the defroster use the AC at all? Thanks for the responses, though. Good stuff!

 

the defroster uses electricity which is created by the alternator. for reasons unclear to me at this moment, the more you use the alternator, the worse your gas mileage is. probably something about putting load onto the pulley system?

EDIT: im talking in very basic terms, and yes, gas does freeze at -97 degrees fehrenheit..so now that i know that, i dunno whats the deal with the stories i've heard about gas companies using "different mixtures" for the winter and summer.

 

when you turn the defrost on the ac compresor turns on to dry the air.

 

OKay, am i understanding this correctly u run the combo of the leg heater and the front defroster because the front defroster uses the fans and heat from the radiator. The back defoster is complety electric. Im gonna do some research about the alternator casue i have never heard of that but does make sense.

The front defroster does not use AC unless you want it too. Usually during the summer and warmer weather when it is raining the defroster with the AC turned on clears up the fog on the inside of your windshield. Unless the AC button is pressed no AC is being used.

 

I really dont think the ac comes on when you turn on the defroster. This is my knowledge from a lot of cars i have been in. I beleive in cars that have auto temp settings the ac comes on all the time whenever you start the auto temp thing. as far as drying the air, doesnt heat dry the air???

 

one day open you hood, turn you car on and switch from vent to the defrost and you can here the ac compresor kick on

 

It's gotta be something big, because I notice that my car lags a lot when either defrost mode is turned on (even without toggling the AC button).

 

Maybe it is different with Lancers casue i ahve never had this problem but i have never owned a lancer just a galant. Ill go and try the ac thing tomorrow on my galant and see what happens.

 

Hey, don't feel bad, my RA gets about 19mpg too, I should really shoot some footage of the gas needle going down, because it really PISSES ME OFF!!! I also drive a MT, shouldnt i get better fuel economy compared to a AT, because I have AT ralliart friends who get better gas than me.

My friend (he owns a evo) laughs @ me because he gets better gas than me. He drives my car and watches (just like me) the needle go down.

 

It says right in the owner's manual that the A/C will engage whenever either of the two defrost settings are selected on the dash - even the the A/C button is NOT selected. And yes, this is done to dry the air more. Heat has little to do with air moisture content - actually the warmer the air, the more moisture it can contain. Having the A/C engaged reduces this effect.

 

Correct, the defrost uses the a/c compressor automatically. Our cars are also programmed so you can't set the recirculate button while in defrost mode (which would make the windows fog up more). Thats where your lag and gas drain are coming from.