Declining gas mileage in my 2001 LL Bean Subaru Outback H.6-3.0


I have a 2001 LL Bean edition Subaru Outback with the H6.3.0. I’ve loved the car but I’ve noticed something peculiar since I moved from Denver to Salt Lake City…my gas mileage has decreased! I used to get about 314 miles per tank in Colorado. Now, I’m LUCKY to get 260 in SLC.

I haven’t changed my driving behaviour. I’ve varied between mid-range gas and premium gas. I’ve had my tires and air filter checked. I think my mechanic thinks I’m making it up.

Last weekend I traveled along I-80 to Laramie, WY and while I was traveling at a higher speed, I did notice a high-pitched sound. Could this be a clue to anything?

'd like to regain that extra 40-50 miles per gallon with these crazy gas prices. Does anyone have any help they can offer? Thank you!


[b]It could be moving from Denver to Salt Lake City is causing the drop in fuel mileage. In Denver, the air is thinner than in Salt Lake City.

There’s a component on your vehicle called a Mass Air Flow sensor. This measures the mass or volume of air that enters the engine. If the air mass decreases, the computer injects less fuel. If the air mass increases, the computer injects more fuel.

So I believe what you’re seeing is the result of moving from a city at a high elevation to a city at a lower elevation.



I agree. Moving from CO around elevation 6000 to elevation 10’ in NH my mileage dropped a bit.


I agree with the previous posters about the air density factor being part of the answer to your problem but it may not be causing all the loss. You didn’t state the milage on the engine but it may be time to change the plugs in the engine. If you do that stick with NGKs. You may want to get the platinum version for longer life. Also replacing the O2 sensor may help get some better mileage as they change over time. I would also check the coolant temperature sensor for the ECU to see if it is showing the correct resistance at normal operating temperature. If it is not correct it will affect the mileage.

I have the same car myself and like it. It has less than 5k miles on it.


Check the tire pressure. The atmospheric pressure is higher, so the tire pressure dropped. I don’t know how much it dropped. It could have been next to nothing.