"Marty" said:
I have a 99 legacy wagon 170,000 kms on it, and have been setting my
tripometer for each tank of gas for the last year, i average around 520 -
550 kms per tank of just regular grade fuel. recently i drove throug the
states and filled up on just regular gas there as well. and was able to
drive 615 - 650 kms on the tank, why the huge difference in milage?
anyone else noticed that their subaru drives smoother quieter and further on
american gas then canadian blends, i even filled up at sunoco i always us
sunoco canadian or american.
Several explanations suggest themselves, listed in what I suspect is
decreasing order of likelihood.
(1) The US trip involved less stop-and-go driving.
(2) It was warmer, and the engine ran more efficiently.
(3) The octane ratings, though nominally the same (87) differed
substantially. Lower octane gas will cause the Subaru engine management
system to retard the timing further, eliminating pinging but reducing
power and gas mileage. I have found substantial differences in gasoline
mileage between different name-brand US gasolines in my 1997 5-speedLegacy
Outback (221,000 km), though all brands were nominally 87 octane.
(4) The US gas did not contain manganese additives, and the Canadian gas
did. This however would be more likely to cause long-term problems with
Canadian gas (catalytic converter contamination, for example -- this is
why auto manufacturers dislike the manganese compounds found in most
Canadian gas) rather than short-term gas mileage reduction.
Instead of resetting the trip odometer, make a cumulative record of gas
purchased and odometer reading, and calculate the average km/L figure. I
do this, starting a new record at the beginning of each year. The average
km/L figure taken from the first of the year will be far less sensitive to
minor variations in how completely you fill the gas tank than the
individual km/L figures, but major changes in performance will soon show
themselves as the average km/L figure begins to drift in one direction or
the other. Some drift should be expected, if driving conditions (highway
versus city, or time of year, for example) vary. I have on two occasions
(with a 1988 Subaru GL 4x4 wagon, not the 1997 Outback) spotted a clogging
fuel filter when the gas mileage began to improve markedly for no good
reason. In each case it dropped back to normal when the partially clogged
filter was replaced. Presumably the clogging was caused by dirty gasoline.
David, 65 km from the US border and manganese-free gasoline
Do you just multiply the distance driven since last