Re: Sudden Poor MPG?? Navigator
I would calculate the mileage over maybe three fill-ups. It sounds like you just figured the 9 MPG based on one fill.
I suspect that if your calculations are correct, then differences in such things as angle of pavement where filled, temperature of fuel remaining in your tank, temperature of fuel entering tank, calibration of pump, etc. may be involved.
To get a reading that is even close to accurate with one fill you would have to fill at the same pump headed in the same direction with the temperatures the same and assume that the stations tank was not recently filled with fuel of a different temperature.
Better to just calculate over a longer period.
BTW I have found that my digital mileage meter is pretty accurate, so much so that I don't even bother checking it any, more.
Then if you find 9 MPG over a longer period you definitely need to look into a possible missing cylinder etc.- Brian
2001 Grand Marquis LS, 25K miles mint (edit; now 56K miles) Finally a vehicle with NO LEAKS !