In my last two tanks of gas, I've gotten real poor mileage (22MPG or less). My gas light came on and I put 12.6 gallons in, but the tank appeared full (tried to top off and got the "click"). After adding an octane booster before filling up (the first I've added to this car), my gas needle was at 3/4 after only 40 miles. Questions:<p>1. Is going from one synthetic (Castrol SYNTEC) to another (Mobil 1) a culprit of something like this?<p>2. Could changing temps (it's now down in the 30s after periods in the 50s and 60s) have an effect of water-in-the-tank or something else?<p>3. I just had the 22500 service, but I thought it was just oil change/fluid stuff, so I don't believe this to be the problem...<p>The funny thing is my "hesitation" in 4th gear at a constant 40MPH is now gone...<p>-josh

Josh, can't offer much - my 98.5 Avant has been pretty consisitently getting 21-22 MPG on semi-suburban/rural running; goes up to about 26 on trips (this is a manual tranny). Your 22 MPG doesn't seem bad, but from what you're saying it's lower than you had been getting.<p>Sudden drop in level seems weird; hope they didn't dent the tank somehow when was in for service (I am assuming this happened shortly after the 22500 service -as in first refill)? Is your A/C compressor on, while before it was off (little "snowflake" on the HVAC panel display)?<br>

If you fill up too fast the gas foams (I think) and you don't fill it up as much as possible. I always put the nozzle on the lowest lock setting and then clean windows, etc. See if this may get you more gas into the tank, and "increase" your mileage.<p>Where do you live? Has it gotten colder recently? The colder, denser air may help get rid of that hesitation your talking about (thus being unrelated to the gas thing).<br>My last car acted the same way...<p>Just some ideas..<p>Mark

I've always had about 21-22 mpg, in suburban conditions. Question: do you live in California (I do). I understand the additives in CA (MBTE) has a noticeable effect on fuel consumption (about 10%). <p>PG, '96 2.8QM <p>

I get around 28mpg with Mobil one vs. 31-32mpg with Amsoil series 2000...both 0W30<br>oils. and the Amsoil stayed much cleaner looking after miles were put on.

The fact that the oil isn't changing color as fast as the Mobil 1 can actualy be a bad thing.

If one oil truly looks cleaner than another after equivalent driving, filtering, and mileage, then the DIRTIER one is doing its job better. It is holding carbon and other stuff in suspension instead of leaving it somewhere in the engine. (It sounded like you were saying the Amsoil was better because it looked cleaner.) There is also the possibility that the oil could discolor somewhat all by itself just due to age and heat chemically changing the oil or additives.

I sampled it at 8500 miles and it would have gone alot further had I not<br>chickened out and changed it...when I switch back I will sample @ 15,000 miles.

I think I've read something about MTBE affecting economy... maybe? I can't remember. I know it sucks for lungs though. <p>I live in SC, which may have a similar climate, but as of now we have no "special" gas. Thank God.<p>Mark