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STS
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Discussion Starter #1
we purchased 2005 STS with 4.2 V8 just took trip from Wisconsin to California and back varied speeds on highway from 70 to 80 mph. best mileage (via computer)was 21.8 mpg. is this normal? my 5.3 V8 four wheel drive Chevrolet Avalanche does this good or better.when we checked on Cadillac it was rated as 25 mpg. on highway what gives?
 

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'11 CTS-V Coupe M6, '05 1SG STS4 V8
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377 Posts
Well one its a 4.6L. Is the STS AWD? If it's AWD then 21 highway is pretty close to average.
 

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2006 STS 1SF N* RWD NAV F55
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705 Posts
Re: poor fuel milage

Depends on What Package you have, which determines what Differential ratio you have.
Anywhere from 2.70 to I think 3.43. I have a 3.23, with the 1SF preformance package,
with Posi. I really like the fact that I have Posi, but wish I could have it with 2.70.
I had a 05 STS, and it had 2.70, and it got 25.
Please check the tag on your spare tire cover, for what package you have.
Even what final drive ratio you have. It's next to the 1SZ number.
Also do you have AWD or RWD ? :stirpot::cool2::cool2:
Happy Motoring
 

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2006 STS V8 AWD, '95 Ford Ranger
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28,963 Posts
Re: poor fuel milage

The build sheet lists a gas guzzler tax for good reason. If you want better gas milage you'll have to slow down below 70MPH.
 

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2006 STS4 V8 1SG & 2007 STS V8 1SE
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8,178 Posts
Re: poor fuel milage

My 2006 AWD wouldn't get that at 80, it's a guzzler; 19 maybe, but gas is cheap. My wife's 2007 RWD with the 2.73 & 6-speed is only turning 2k RPM at that speed & 25 MPG just takes tires harder than I like, say any set of Michelin rocks.

It had the worst example, the Pilot Energy, on it when she bought it. With less than 30,000 miles and lots of tread left, they were dangerous in any but perfect conditions, even with traction & stability control.
 

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2006 STS
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Re: poor fuel milage

I have a 2006 STS V-8 and I got nearly identical milage on a trip last weekend. I got 21.6 on a 650 mile trip (nearly all highway miles) from Las Vegas to Flagstaff, AZ driving 70-85 mph. Temp was 110F so the AC was on non-stop. I'd say 22mpg is average for my highway trips driving 75-80. I had a Lincoln LS V-8 before the Caddy and it would consistently do 25mph on a trip but the Caddy rides better!
 

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That's pretty good ! My '05 overall average is 14mpg. But I live in metro NYC the stop and go Capital of the world.
 

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I get around 14-15 mpg, 2005 STS V8 RWD 1SG with 3.42's and the 5 speed. Wish I got 21, but I didn't buy it for fuel economy...
 

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2006 Cadillac STS 1SG
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Mine seems to be averaging about 17-18 around town, and 24-25 on the highway, usually scooting along at 75-80. 1SG and 3.42s as well.

The cruise control is a nice feature.
 

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2006 STS4 V8 1SG & 2007 STS V8 1SE
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8,178 Posts
I love the ACC, but it does cost some MPG since it uses braking when traffic requires. At least it only uses the rear brakes, so I don't really notice increased pad wear.
 

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2005 STS N*, 1SF, 144K mi.
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650 Posts
I barely crack 20 in combo city/highway (20%/80%) in Fort Worth, TX. 1SG, V8, 2WD, 3.23 posi diff. The STS isn't the most aerodynamic nor light vehicle.

Yuh gotta remember, that's a 320 HP V8. I'm not complaining.

My '98 5.9L Grand Cherokee barely ekes out 15 MPG doing the same commute.
 

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2005 STS 1SG
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I barely crack 20 in combo city/highway (20%/80%) in Fort Worth, TX. 1SG, V8, 2WD, 3.23 posi diff. The STS isn't the most aerodynamic nor light vehicle.

Yuh gotta remember, that's a 320 HP V8. I'm not complaining.

My '98 5.9L Grand Cherokee barely ekes out 15 MPG doing the same commute.
How are you getting those #s? I have the exact same make model and year and get 14.5 to 15 on a good tank...
 

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2006 STS V8 1SF RWD
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How are you getting those #s? I have the exact same make model and year and get 14.5 to 15 on a good tank...
Depends on how you drive and where you drive. A heavy foot and lots of stop and go will not get you decent mileage. I've gotten mine over a 20mpg average plenty of times but that is 90% freeway.
 

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2006 STS4 V8 1SG & 2007 STS V8 1SE
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Some gas blends will be worse, but my STS doesn't seem to care as much as the 32-valve 4.6l V-8 in my previous car, a Lincoln Continental. 87-octane Ethanol cost it 1-2 MPG; higher octane didn't help much, pure gas did.

Open windows cost mileage, as will low temperatures, even if you don't warm-up your engine (generally not necessary under normal conditions.) Mileage is almost always driving style or technique. Do you tailgate or drive looking at traffic two or three (or half a dozen cars) in front of you? Every time you touch your brake pedal, you threw-away gas. Above 2,000 RPM the Northstar performs great and sucks gas.

Do you brake with your right or left foot? Studies have proven it is almost impossible for a left-foot braking driver to not occasionally rest their foot on the pedal, drag the brake pads, costing mileage and wearing brakes.

Maybe something is wrong with the car. Is your temperature gauge always 1 tick mark below midway? Low engine temperature (a bad thermostat) will cost mileage, too. The biggest gains in the newest cars city driving numbers are due to stop/start technology instead of idling.

The STS DIC has an Instant MPG setting. It can help teach driving for mileage. I'd rather drive like I stole it. :)
 

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2005 STS N*, 1SF, 144K mi.
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650 Posts
How are you getting those #s? I have the exact same make model and year and get 14.5 to 15 on a good tank...
I'm gentle on the accelerator, and as soon as I see traffic slowing or see I'm going to have to slow down or stop, I back off the gas.

The key is most people must have one pedal in use at all times! No, that's not at all efficient.

I'm not plodding along at 45 MPH on the freeway or 25 MPH on side streets, either. Freeway is typically posted (which is what traffic is moving at), and surface streets are 5-7 over posted (usually).

If your travel includes any of the five boroughs, you're hosed. I'm in Texas, so much of the freeway stuff is steady, though I do have a decent drive to get to said freeway. Some days, and it doesn't happen enough, I manage to hit every single light green. Other days, every one is red.
 

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2006 STS 1SF N* RWD NAV F55
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705 Posts
Forgot one thing, with you guys who have over 100K miles,
Have you changed the Spark Plugs, yet ?
I changed mine @ about 86000 and I am gettin getting
Highway Min. 23, and at times 25 like I am supposed to.
tires COLD @ 32.City 13, BOOOOOO
Intake manifold bolts LokTited, new Plugs and fresh oil MOBILE 1.
Happy Motoring, Hope this Helps
 
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