Bad MPG on 2008 Lucerne

Thread starter #1
Buick Ownership
Hello everybody,
I'm hoping to get some useful information here.
I bought 2008 3.8l CX Lucerne with 191.000 km (118.000 miles) in August like my project car.
I did all the necessary work and I really enjoying driving my Lucerne, but my fuel consumption is very bad.
When I bought the car on display was shown average of 12 liters per 100km (24 mpg)When I was driving car home due to car condition I was driving 90 kph on highway and instant consumption was showing 6 to7 liters (47-40 mpg).
After all the repairs I start driving car in the city, but I couldn't get better than 17 mpg.
I live in Canada and when winter came it jumped to 20 liters (14 mpg).
I changed the air filter and aded a can of Sea foam in fuel but that didn't change anything.I get fuel only on good gas stations.
I did all brakes and all pistons are good, and sliding bolts are good to.
I don't know if this is maybe normal for this car?
I drive only in city, all my rides are less than 15 km and temperatures here are from 0° Celsius to -12°(32-10 ° F).
Should I maybe change spark plugs next, or this is normal for this car?
Buick Ownership
2007 Lucerne CXL. and 1995 Lesabre currently, past 1973 Riviera, 1968 Riviera
If it's the original plugs and wires with 118 miles, yes as it may be time. But winter is brutal on gas mileage so you may pick up some but it may only be 1 or 2 mpg. Check the tire pressure and type of tire as that will also make a difference. Some places may set the tire pressure to the door spec but I've gone higher based on the tire spec and have had no problem, but you should talk to a tire shop about this before doing it.

Here's what that car milage ratings are.
Fuel Economy of the 2008 Buick Lucerne
Buick Ownership
I think they just don't do so good. I had a 1998 Park Ave that averaged 22 mpg and 28 mpg on long highway trips. Those numbers were constant from the time I bought it to when I sold it with 197,000 miles. I went from that to a 2008 Lucerne and I can't get better than 20 mpg and 23 mpg highway. I figured the Lucerne should have at least been as good if not better than the much heaver Park Ave. When I pointed this out to the dealer(s) all I got was a lot of crap.
S.W. Ontario Canada
Buick Ownership
2018 Regal Sportback - 2010 Yamaha R6 (track bike) Past cars: 92 LeSabre, 98 Regal, 02 GrandPrixGT
12 L per 100 km is 19.6 mpg. but I assume you got the idea of 24 mpg from the Imperial British Gallon and not the US Gallon.

In reality, around 13.5 L / 100km (17 US mpg) is what you should expect in the summer and closer to 14.5 L / 100km (16 mpg) in the winter for city driving.

Weight of the vehicle and final drive gear ratio affects fuel economy greatly.

I had a 98 Regal 3800 with a final drive of 3.05 and I was getting 11.5 L/100km in the city. Then I had a 02 Grand prix 3800 with 3.29 final drive and I could not get better than 13 L / 100km.
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