I don't see a thread about gas mileage, is everybody satisfied with what you get? what is your hiwaygas mileage on your Grand Marquis?this last weekend on Sunday I got 30.4 I have a scanguage hooked up.anybody using additives in their gas?

Grand Marquis Fuel Mileage
 

This is a very old thread, but bears renewing for the benefit of the few who still own and drive the fabulous Mercury Grand Marquis.
In order to find your ACTUAL fuel mileage, an accurate measuring system is necessary, and a log book to record the date of the findings.
To measure fuel mileage ACCURATELY, record the amount of fuel purchased to TWO (2) decimal places (00.00).
Recorded info includes: Odometer reading -- Gallons used -- Price-per-gallon -- Amount paid -- Time-of-day -- Date -- City, State.
Example:
Previous odometer reading: 167,315.
167,575 / 15.95 / 1.219 / 19.45 / 08:00 / 11/17 / Phoenix, AZ
167,575 - 167,315 = 260 miles @ 15.95 gallons =16.03 mpg
Using 2 decimal places allows for incremental differences to indicate a mileage drop-off that requires attention.
I have used these same fuel mileage calculations since 1972, on cars, pickups, and SUVs.
On the 95 MERC, fuel mileage is relatively consistent at 16 City, 24 Highway, using 87 Octane Chevron gasoline.
Every 5,000 miles, a 20-ounce bottle of Chevron's "Techron" Complete Fuel System Cleaner is added at fill-up.
Oil Changes @ 5,000 miles -- Full (not a blend) synthetic oil, API Service "SP" -- Bosch # 3410 Premium Oil Filter.
Passes yearly Emissions Test with excellent results.
https://cimg9.ibsrv.net/gimg/www.mer...d8bb92bac3.jpg
95 MERC Engine Bay