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Snuffy115 12-09-2010 06:38 PM

Can a flaky alternator cause....
Can a flaky alternator cause a drop in mileage?

I buy my gas primarily at the shell station a block away from my house.
I've always tracked my mileage. All summer I've been getting high 17's to mid 18's for mileage. Occasionally in the mid 19's with a lot of highway driving. Through mid November I was still getting lo to mid 17's.

Filled up on 11/12 with 17.6mpg for the previous tank
Oil change on 11/13
11/18 Fill up 16.6mpg
11/26 fill up 16.8mpg
12/3 fill up mpg to be determined on next fill up.
I will need to fill up either tomorrow or Saturday.
I'm almost on E and I'm only at 275mi for the tank. I should be over 300.

It's been below freezing, here in Chicagoland, for the last week. The alternator is squealing in the morning and my volt gauge looks a little low. I've also needed to jump it to get it started every morning this past week. The battery is an Optima red top no more than 3 years old. The alternator was replaced this past spring during my restoration project.

I'm thinking I have a flaky alternator. I'm just not sure if it will cause my mileage problems as well. My mileage hasn't been this bad since the fuel return line was obstructed a few years back. It got down to the low 14's then. I haven't checked the fuel pressure yet.

Any thoughts?

Also worth noting, This is the first winter with a K&N cold air intake on it. I don't know what to expect, regarding mileage, in the cold weather.

Jeep716 12-09-2010 08:00 PM

Could be winter blend fuel. Fuel here in NY is 10%Alcohol. That kills horsepower and mileage at least 10% in most vehicles. I'm lucky to get 230 to 250 out if a tank in mine. That's with a 2.5 added leaf and 33's. 5sp and stock gears.

hannahuffster 12-09-2010 08:23 PM

Is the gas pumps saying you are putting about the same amount of gas in each time you fill up? Your not relying on the good ol' yj fuel gauge each time are you?

Fweaky 12-09-2010 08:35 PM

In colder weather the fuel mixture will be much richer until the engine warms up.

ISUSteve 12-09-2010 09:42 PM

I'm in Iowa. I think they switched to the winter gas a few weeks ago. I've noticed a significant drop in all my vehicles.

Its okay though, its also about 50 cents higher.

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