Gas Mileage?

[BodybyFisher]

I concur Brad, around town 16 to 17, on the road 23 to 25, Mike

[JasonA]

I used to be of the camp that said fuel didn't matter, but I've accepted that it really does depend on the vehicle. I saw a driveability drop when I ran 3 tanks in a row of 89 octane. I didn't even get down to 87. The car definitely runs best using 92.

As for mileage, I like to think I drive it "smart". Among other cars, I drive pretty easy. Nowhere to go, why waste the gas? But I still get on it hard at least 2-3 times a day, when the road is open. Living in a flat area certainly helps. And it's not like Fayetteville, North Carolina, compares to New York City in terms of traffic.

The SLS gets good mileage anyway because of it's taller final drive (3.11 vs. 3.71). I also keep the tires aired up...38 psi front and 30 psi rear. I'm beating the EPA city rating by a full 5 mpg now (17 vs. 22).

I used to drive the car much harder than I do now. But I've really started to enjoy the Cadillac for its smoothness and class, and not for its speed. And I've tended to drive that way over the past year. The smoother I drive and the fewer times I "race" a ricer, the better economy I get. It's steady increased since the time I got it, probably from me slowing down and driving smoother.

I take a 380 mile trip at least once a month from So. Cal. to Mesa, AZ. I run 75 mph for the first 200 miles, and 80 for the final leg on the AZ side. I get a disappointing 21.7 to 22.1 in my 2001 DTS on these highway trips. My old '97 DeVille did much better, averaging high 24's into the mid 25 mpg range. The mileage always drops in the AZ segment of the trip. No surprize, I guess, but it is amazing that an extra 5 mph can drop the fuel economy by 1 or 2 mpg. I usually use Chevron gas.

There are more factors at play than speed alone. The DTS has a 3.71:1 gear and your old DeVille probably had a 3.11:1 final drive.

Wind resistance increases exponentially as speed increases. There is a point of diminishing returns...as you fall below 40-50 mph, wind resistance isn't really a factor. But start driving faster, and even 2-3 mph can make a big difference over the course of a trip, especially in a larger vehicle. The EXACT same trip in our Grand Caravan returns FOUR mpg better by driving 65 mph vs. 70 mph.

[JimHare]

Around here in Salem, it's mostly suburban two-laner's averaging 45-50 when moving. Not a lot of stop and go at all. Occasional 10-15 mile burst up I-295 or something just for the exercise. WOT at least 2x a week.

I get 21 in the Eldo on Sunoco Regular 87 octane.

Never really had it on a long highway trip to determine that kind of milage, but I'd imaging I could hit 25 mpg if I tried.

Melissa in the Deville, who's got a heavier lead foot than I do, averages 22 mpg also on regular gas. She does a lot of turnpike driving, and a fair amount of around-town stuff in northern NJ, such as trips to Princeton and Edison, etc.

On a recent trip to Florida the round trip and the week spend futzing around Vero, Ft Pierce and Palm Beach, the overall mileage for the whole trip was about 25 mpg, if I remember.

My tips: 34 PSI in the tires, slow on the take off after first start in the AM, get to cruising speed quickly but don't mash the throttle from a stop, and anticipate the stops ahead - I do a lot of 'coasting' to those red lights up ahead when I see them...that's maybe why my brakes last 80K miles, too...

[Monaco500]

I have a '94 STS with 140k miles. I usually average 21.5 in the summer and 19.5 in the winter. About 1/2 highway driving, 1/2 city. I use midgrade with no additives. Lately, my mileage has been dropping to 18, and I've had problems with the rpm surging when accelerating slowly. Usually it will recover if I take my foot off the gas, but lately it has been stalling. The error codes refer to an open and intermittant MAP sensor, even though I have replaced it recently (the old one had oil residue on it - normal?) and hot rear oxygen sensor. Any thoughts?

Eric

[JasonA]

Eric,

If one of your oxygen sensors is so far off to set a code in the computer, I'd say that's probably the reason for your poor mileage. I would recommend only an ACDelco oxygen sensor. I've tried other off brands before (like Bosch) on other GM vehicles with poor results. Also check other common items like the condition of your spark plugs, spark plug wires, etc.

My uninformed opinion about the MAP sensor is that a slight residue is probably normal, depending on where exactly the MAP sensor is located. If anywhere in the intake manifold, you have exhaust gas circulating around in there, as well as PCV vapors, so I'd say a build up over 12 years would be very normal.

Good luck,