Sudden MPG drop

[bob/cathy]

Have 6000 miles on our Passion.Changed out the ,'what have you ',oil at 2000.
Car runs great,probably 45/47 mpg+. We filled up last Sat.92 miles,couldn't get 2 gallonl in,actually 1.96.Did the same yesterday,same Cheveron station,3.2 a gal. 12 bucks even.Now with 26,8 miles see the gage has dropped.
What might cause this.I bought,'91 oc.',if they had lower oc. in the tank or what.If a plug was bad sure you would feel that.Has anyone suspected a station might put a lower grade fuel in their tanks?
Guess the fuel test would be to fill up at a different place than call the state of Utah and raise hell,if all was better.Will do first half,tomarrow.

[babybenz]

Ethenal would be a factor

[Dunerunner]

You cannot validate fuel mileage by the dash gage. It must be done by recording the start and end mileage and calculating the mpg as a function of the gallons of fuel required to refill the tank to the same level before the mileage run was made.

[Old smart]

A mis-firing plug will give a CEL and throw a trouble code. I think you would feel one out of three yourself.

Some locations change to Winter blends in the fall, but those usually contain less anti-smog oxygenates (better).

Judging mileage using the gas gauge readout of a couple of gallons is a pretty crude method - you might try comparing multiple full fill-ups.

[bob/cathy]

Of coarse Dun.,we did that at first but it gets boring. The mileage I mentioned and the fill up is the same thing.Has anyone saw their gage drop the first 'bar' after 27 miles? Bet if someone tried useing a lower grade,they might see this. And the ethanol might be a factor but not that much.But thanks for the input.

[bob/cathy]

Didn't mean it as a method,but rather a wake up call.Never saw it drop befor 90+ miles,but will check with a different place for sure.I'm not old enough to be smart,but did live long enough to not let the tank get below 1/2.
Just thought someone else had the same thing or the gage some times gets flaky.

[forestacademy]

At lot of folks gage never goes to full.

Don;t worry about the top 1/2 of the gage. Fill it up when it gets below 1/2 You cant gage MPG with just 2 or 3 gallons.

Even with a full 8 or 9 gallons .2 gallons can give you a big discrepancy.

Example: Car has 300 Miles on it You put in 8 gallons you get an MPG of 37.5
If you squeeze again and now have 300 miles and 8.5 gallons you suddenly only have 35.3 MPG

Also, It is not a good Idea to let the tank run down to almost empty because you could damage the fuel pump and see a $600 repair bill. At the same time it is not good to top off your tank because you could flood a filter and have to go get something else fixed for a price I haven't heard yet.

Either way, run your tank between 1/8 and 7/8 and you should be fine. Put some miles on it and at least 3 fill ups like that and call us in a week, or 3 to let us know what your mileage is.

[John_H]

The top of the gauge appears that it will refuse to be accurate. Have you heard of the "7/8ths issue?" There are those who *fill* and only get 7 bars, then after 50 miles or so read a full 8 bars.

Your mileage cannot be calculated with the smart's fuel gauge.

[ibking]

Me too, AFTER THE TURBO WAS INSTALLED. I like it.

[SmartDigger]

I think you had a fill up with a sensitive auto shut off valve.