can anybody help me :?: i get about 18 to 19 mpg at best, and that is mostly highway driving. is the onboard computer acurate?

Check your o2 sensor. Do you have access to an autotap or someone with one?

Your mileage will vary drastically depending on your driving style and driving time duration.
Sure these cars can achieve over 30 mpg on the highway driven steady state with no accel or decel but in real world driving with relatively short 1/2 hr trips or with some idling at stops, that mileage can drop to 15 mpg.

I usually average 15 mpg in town but have dropped as low as 12 mpg. Steady state in town driving, I can get 26 mpg. at a steady 40 mph.

1 gallon= 4.546litres in canada
1 gallon=3.78litres in usa

I average around 26 miles per gallon with combined driving.
As much as 32 miles per gallon on trips with the cruise control

and yes those are canadian gallons

Well I'm heavy footed and make short trips on the highway everyday and my DIC says 16-17 mostly. Can get it up to 26-28 cruising on the highway though. But no fun with out accelerating, my highway trips average 17-18.
It'* not my o2 sensor either!

PontiacDad makes a good point but I would be willing to bet that the DIC reads mileage in Liters/100Km or miles/USgallons.

Yep I was right. 15 L/100KM = 15 mpg if I toggle the DIC English/Metric button.
But if you calculate 15 L/100 KM and convert it to miles/Cdngallon, you get 19 mpg.

In most industries, if not all, in Canada, we use USgallons because most of the equipment we buy from the US and the specs all quote USgallons.

I think I'll just stick to comparing in Metric units, that way we are all consistent, but remember all you other Canuks that if you use the DIC English units that it is in miles per USgallon.

I would say that gas mileage is normal. These cars are heavy, big, and lets face it, they don't have the most efficient engines. The DIC in my moms SSEi has never been reset since we bought it new in 2000. The car now has 90,000 miles on it, and the DIC reads 20.8mpg. Most of the miles are highway miles, but when it does get city driving, it isn't nice city driving, we do beat on it a bit. But, I wouldn't even expect that gas mileage, because before the rockers the DIC was reading 1mpg lower. It is slowly but surely going up.

But if you do want good gas mileage I could help you out a bit. With the cruise set at 76mph in the GTP for 40 miles of highway, and 60 for 30 miles of country road with some WOT passing, and getting back up to the 60mph at WOT after stopping for stoplights (to teach the PCM a bit), the GTP averaged 37.2mpg. Now, that was on 100 or 104 octane race gas (i can't remember for sure), but it doesn't do much worse than that on pump gas. If we don't ever reset the DIC it seems to average right around 25mpg, and it is driven almost all city, and a lot of it with a heavy foot. Because of the freer flowing air intake and exhaust the engine is more efficient and therefore makes much more horsepower, and gets much better gas mileage.

So, the moral is, if you want to get good gas mileage, dump $10,000 into your engine, and you will, it will probably just take a while for the gas savings to make up for what you spent.

I'm working on it! Mega Stereo went in first.

I do'nt think they are bad...I average about 750 km to a full tank. That'* about 469 miles.

For the last couple of weeks while my car was being fixed, I was driving a 2003 DeVille with the northstar engine. The mileage on my Bonneville is averaging 16.5 mpg. The DeVille was showing 17.5. I thought that was odd, but I guess it makes sense. The Caddy has a multivalve v8, probably working less hard to pull that car around, even though its heavier.