98 Grand Prix GT 3800 Bad mileage

[richtazz]

Performance shift is only on GTP supercharged models, so that is irrelevant. Your combined city/highway figure of 19.2 mpg is on the low side of normal.

I have purposely varied my driving habits and have come up with the following:

In my 99 GT, I can get as high as 22-23 if I drive like a grandma and don't sit at drive-thru's, but average closer to 20.5 to 21 mpg if I drive normal (and have experienced as low as 19 if I'm a little more aggressive). On trips, if I keep it around 70-73 mph, I can average better than 30 (on a long trip at 65mph though Ohio, I got 33+). At 75 or higher, there is a significant drop in mileage (only 25-26 mpg).

Driving habits have a big impact on economy!

[jr566]

Make sure the perf switch is off. Usally located on the left side of shifter. If on will greatly reduce gas mileage.

[BNaylor]

Originally Posted by jr566

Make sure the perf switch is off. Usally located on the left side of shifter. If on will greatly reduce gas mileage.

Are you referring to a GT/SE or GTP? The members that posted in this thread that are having mileage issues don't have performance shift since it is only applicable to a L67 GTP.