my girlfriend has a 2001 expedtion with the 5.7 v8 and yestrday by accdentu filled it up with premium and she telling me she is telling me she seems to be going thru the gas really fast. it does not seem normal if anything i thought it should last longer. am i wrong or what im not really sure what is going on? thanks for any help in advance

 

It's all in her head. Premium if anything, gives you slightly better gas mileage.

 

also notice better gas mileage w/ prem. 5.4 im getting avg 12 city 17or so hwy...w/ 87&89. 91-93 It tended to stay closer to 14-18. About the same for everyone else?

 

shes telling me in about 47 city miles she went from full to 3/4 and i belive it has a 30 gallon tank correct me if im wrong beacuse i could be but if its 30 gallon tank using 1/4 tank is 7.5 gallons the only other thing i thought of it wasent really full and for some reason the gauge was reading full.

 

Its very dificult to tell how full these tanks are, what with the baffles, vent lines, and the fact that the filler neck is at the very rear of a long narrow tank. And if I recall correctly, the filler neck does not go into the top of the tank - I think it goes into the wall of the tank, so its hard to tell just how full it is. Was the truck parked on a slight slope when she filled it? Was it loaded or empty?

 

I have never seen a fuel gauge that was accurate through its range. The only way to determine milage with any accuracy is to burn several tanks though.

I seriously doubt there is any change in milage, much less a drastic one. The higher the octane rating is, the more difficult the charge is to light off and the burn is slightly slower. The engine in her truck was not designed to take advantage of the higher octane so there is no performance increase, possible a slight decrease. The fuel injection computer can not sense the higher octane either and is distributing fuel as it would if it were low octane.

Tell her not to worry about it, no harm no foul.

 

I agree 100% with "Big Greenie", the vehicle is designed to run regular fuel. Running premium would make no difference in fuel economy or power. The only reason to run higher octane fuel is if your vehicle is set up for it, like a engine with high compression or power adders etc. Unless the vehicle says to run high octane fuel there is no reason what so ever to run premium.

 

I wouldn't run Prem gas unless it was tuned for it to get Max Horsepower. I had a H/C/I LS1 Goat for 3 years that ran only Prem gas, if you put 87 Oct in it you would know it as soon as you cranked it. However on a stock motor set for 87Oct.. I wouldn't touch Prem gas.

 

Would it cause additional carbon to build up around the un-sound plug design to run prem? Thankfully runs great on 87..and after three tanks thus far the avg is 13.9 steady on regular, however accurate that may be.