Hey guys,

 

I bought a 2009 Forester XT about 2 weeks ago and reset the MPG calculator while I was on the freeway and was getting about 33 MPG. Since then I've been filling up with premium like it says, and all of a sudden I'm only getting 25 MPG on the freeway.

 

I'm not sure if the dealer had it filled with regular gas when I bought it, but I'd really like to get that 33 MPG back! I've been driving it the same way the whole time too. Is there any reason why I can't just switch between regular and premium gas every other tank, or maybe get mid-grade? Would regular be bad for the engine but give better MPG?

 

Thanks,

Owen

Welcome to the USMB.

 

If the car requires premium the ECU is going to be tuned to take advantage of it, and run more timing, which does improve mileage. So if you run regular grade, the ECU could pick up knock and retard timing a little bit, which will decrease mileage.

 

As for your current decrease in mileage, you could have gotten a bad tank of gas, or the ECU has just learned the your overall driving habits and adjusted. This is usually a case when driving mixed, highway & city.

 

You could try resetting the ECU by disconnecting the battery cable for an hour or so and then see if that brings the mileage back to what it was.

 

Personally, I don't really trust the computer mileage readings, so you may want to do your fuel mileage by hand and compare it to what the computer says. Also, I think the 25 mpg is more what I would expect to see from that car, rather than the 33.

Yup, 33MPG is way above what that SUV is rated for on the highway. It's designed for premium and will run best on it. 25-28MPG for highway is what I would be quite happy with. Also, the computer "MPG calculator" on my folks 2006 OBXT is rather...."optimistic" in its math. Divide your total miles driven by gallons used to find out your exact MPG.

 

Remember you have an all-time AWD SUV with a turbo charged engine...it was not exactly designed for Prius level MPG.