I've read what most of you have posted about Franks Email.

Some of you may have had it right and a few have missed it.

So I send you to the one place that has all the facts.

I filled my 01 Subaru outback with 93octane earlier today. I drove from the my brothers to my house, which is all hills and then a shot on the highway for about 30 mins. Filled it back up, and punched the numbers 33.9mpg! That car never got more than 23mpg on a good day on 87. I am sold on Premium now.

Also, I did not change my driving habits either. <img src="/forums/images/graemlins/butwiggle.gif" alt="" />

Did you go back to the same station, use the same exact pump handle and fill up to the exact same level as when you started? I've never heard of someone adding about 50% to their gas mileage by using premium over regular. Do a longer-term test and see if this continues to play out, would ya?

One other thing about filling up that I've wondered about: Will the vapor recovery system actually "recover" some of the liquid fuel you've already been charged for as the tank in the vehicle reaches full? Not like it would suck fuel out of your tank, but some drops, etc. That could mean a collective significant amount over hundreds of cars over the course of a day/week, etc. Could those systems be operated more "aggressively" to pull more vacuum to enhance that effect?

John B.

I am going to continue checking mileage and do some long term testing. I was wondering why my needle barely budged during the trip, I would normally be down a 1/4 a tank doing the same trip any other time on 87 octane. It's very possible the Outback was made to run on premium from the get go, and using regular could be the cause of the poor power and $hit gas mileage. I just found it funny, that it is getting better mpg rating than what is advertised it should get. <img src="/forums/images/graemlins/lol.gif" alt="" />

If it was designed for premium, but has been running on regular, how much of the new tank of gas was the premium?

I know my '95 with the 3.5l will run on regular, but it will pull the timing back as required by the knock sensor for slightly less power and likely lower mileage as well. I drive it so infrequently now I just spend for the premium anyway.

Keep us up to date on this.

John B.

I filled up when the gas light came on, so only about 2.5 gallons of Regular/Midgrade mix(I put 89 in at the half mark a few days before) should of been in the tank at the time. I noticed about 5-10 miles the engine started to run alot smoother and lost alot of the hesitation it was giving me previously. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Wife's subie does the same thing. It pulls back the timing when it hears regular grade ping, and you lose hp and mpg both with the retarded timing. I added some octane booster to premium once, and picked up 4mpg and what felt like 10-15hp. Giddy with power, I almost ditched it when it came on the cams coming out of a corner and it broke traction under heavy right foot on all 4 tires at once. THe only time I miss 2wd is when that happens. Can't kick the tail out with the happy pedal any more, it just loses bite on all 4 and slides straight from the breakaway point....