Surprising fuel consumption

[TdM]

Last night I was driving from another city and I was driving about 75 Mph (120 km/h), on cruise control, minding my own business, and I checked on regular base the display which said that my average fuel consumption was something like 9 liters per 100 Km or 23 mpg. It was a 2 hours drive and my average was about 10.1 liters per 100 Km or 24 mpg.

I'm impressed about that fuel consumption and I didn't expect this. Had a '94 Ford Explorer (4.0 V6), a '95 Jag XJ Sport (4.2 V6) and a '88 MB 420SE (4.2 V8) before and they didn't came even close to this consumption under the same conditions. I can imagine the Explorer coz it has no aerodynamic and weight about 200 Kg more. I'm checking the air pressure in my tires regular so... that's not the issue I think.

How is it possible that a STS with this kinda engine is almost more economic with the fuel then a average midsize car on long distance?

City use is a totally different story... but I drive about 95% highway and 5% city... so who cares about that.

Of course... I'm not complaining

Now I'm curious... how much does your car does on Highway use?

[Cadillac Jim]

I routinely get 23 mpg on the interstate with my 1997 ETC (300 hp Northstar) at about the same speeds when appropriate to traffic flow and speeds. I would be concerned about a tuning problem if the mileage dropped below that. The 23 mpg is an overall figure for the trip and includes gas and food stops and the cold start at the start of the trip. My usual lead foot is on hold except for emergencies because my wife is in the car.

[epricedright]

I just returned from a 1700 mile trip and I averaged 27 on the highway, and 23.6 for the whole trip. That included a LOT of stuck in standstill traffic, circling around parking lots looking for a space, etc. in Destin, FL. My mpg would have been higher if the Caddy wasn't loaded down with 4 passengers and COMPLETELY stuffed with luggage and what not. We were loaded down to the gills - not one square inch of space left in my huge trunk!

[thu]

I have an '03 STS (300 HP Northstar) and I get 24-26 doing 85 MPH.

[GreenMachine]

My kentucky wedding trip average 24.6 for the whole trip, by my own calculations thats could have been higher, especially when you factor in...ummm my lead foot getting back on the highway after stop...and the one time I took it up to the 112mph governer..it was clear...I had too to see if it was really there....anway. A few stop and go situations also caused it to drop. It was mostly 70-85mph driving, 70-75mph the car cruises around 2000RPM and that ain't bad.

When you look at the torque/hp curves on the graphs from GM you'll see that they designed these babies cleary for best highway crusing in the 65-75mph range (parts of my trip where it was flat and slightly down hill 80mph was nice to cruise at with instant saying something lke 33-40mpg .

The other factor is not just strait instant MPG but also the less time you take to travel, the less fuel you use...thats can be easily messed up if you start lead footing like I have a tendancy to start to do.

[JimD]

Every possible combination of driving you can imagine from idling in dead stopped traffic to abusing the limits on the Interstate at 3:00 AM and everthing in between; 148,809 miles and 7,032 gallons of fuel = 21.16 MPG.

Maximum = 27.27. Minimum = you don't want to know.

[JasonA]

How is it possible that a STS with this kinda engine is almost more economic with the fuel then a average midsize car on long distance?

Because these are excellent powertrains, that's why!

I average about 20 mpg city and 30 mpg highway (speeds 65-75 mph). Nobody believes that I get 30 mpg from a V-8 engine.

[BodybyFisher]

It is amazing isn't it? And consider this....if you drop to 60, watch your gas mileage increase, you were running 75...

On a recent trip I averaged 22.5 over 1200 miles with AC on, 95 degrees plus, four big guys, luggage at high speeds with stop and go and low speed driving added in. Pretty good if you ask me.

When I reset my mileage indicator on the highway doing 70 I regularly average 25 to 26 MPG..

This is a very efficient engine

[TdM]

It is amazing and I start to love this car more and more. Except my small AC problem I never regret that I bought this car.

Never thought a Caddi with so much power would be this efficient.

The only thing I think what could be better is the Dash shining in the front window at daylight.

B.t.w. If you use the parking break... how to release it? Checked the Owners manual but couldn't find it.

(http://myweb.accessus.net/~090/resources-cad.html#new)

[BodybyFisher]

Your parking brake should release on its own. There is a vacuum servo as part of the parking brake assembly, if you look up in there. Check for a broken or disconnected hose. However the vacuum servo goes bad and can be replaced.. See this thread by Scotty...(that's me!), its for a 91 BUT the concept is the same for your car..

http://caddyinfo.ipbhost.com/index.php?sho...hl=vacuum+servo

By the way, there is a manual release that you can pull, until you get it fixed...

Here is your owners manual:

https://www.mygmlink.com/pdf/go2content/man...1993seville.pdf

See Page 89...for parking brake info and release

Use Adobe Acrobat to read this PDF file, and use the search function

[GreenMachine]

^also if you set the brake and just "go" it usually wont go up all the way, put it it reverse, wait a second, it'll go up, then go. Also applying the brakes while shifting and holding them there while it pops up helps it out.

[TdM]

No.. it's cool. The parking brake is working.

I couldn't find how to release it so I didn't use it... kinda stupid when you're at the shopping mall and can't drive coz you don't know how to release the parking brake

I was used to release the park break manually. Living in a flat country anyway... so P should be enough

But I kicked it... put it in D and it came of just fine...

[BodybyFisher]

Another nice feature of your Cadillac!

[JasonA]

The only thing I think what could be better is the Dash shining in the front window at daylight.

My brother's Corvette has the HUD (Heads Up Display) and I think it should be a standard feature in every single car. It's an incredible safety feature -- even a die-hard gauge watcher like me doesn't ever look down from the road with that HUD. It's all right there. Speed, RPM, etc. I can't think of a feature I'd rather have MORE than an HUD on every vehicle I own.

[WarrenJ]

I can't think of a feature I'd rather have MORE than an HUD on every vehicle I own.

Yup, but it'll have to remain a dream for me, for a while anyway.

Regards,

Warren

[Paul_tunney@hotmail.com]

I can't think of a feature I'd rather have MORE than an HUD on every vehicle I own.

Yup, but it'll have to remain a dream for me, for a while anyway.

Regards,

Warren

you'd be surprized i owned a 92 pontiac bonivelle with hud, most pontiacs run it as an option, i thaught i was on the caddy's as well

[BodybyFisher]

It sure did...

http://en.wikipedia.org/wiki/Head-Up_Display

[Texas Jim]

Last night I was driving from another city and I was driving about 75 Mph (120 km/h), on cruise control, minding my own business, and I checked on regular base the display which said that my average fuel consumption was something like 9 liters per 100 Km or 23 mpg. It was a 2 hours drive and my average was about 10.1 liters per 100 Km or 24 mpg.

Now I'm curious... how much does your car does on Highway use?

Just came back from a 700 mile trip. Some interstate, some 2 lane highway a small percentage of city driving. <Houston Tx.> Tried real hard to keep a fairly light foot.

From Ft. Worth to deep SE Tx ... 21.5 From Houston back to Ft. Worth, going the long way, not on I45, 20.5.

I envy all you guys that get 25 to 30 MPG. My '06 DTS don't even come close to that. I wish it did.

[BodybyFisher]

Last night I was driving from another city and I was driving about 75 Mph (120 km/h), on cruise control, minding my own business, and I checked on regular base the display which said that my average fuel consumption was something like 9 liters per 100 Km or 23 mpg. It was a 2 hours drive and my average was about 10.1 liters per 100 Km or 24 mpg.

Now I'm curious... how much does your car does on Highway use?

Just came back from a 700 mile trip. Some interstate, some 2 lane highway a small percentage of city driving. <Houston Tx.> Tried real hard to keep a fairly light foot.

From Ft. Worth to deep SE Tx ... 21.5 From Houston back to Ft. Worth, going the long way, not on I45, 20.5.

I envy all you guys that get 25 to 30 MPG. My '06 DTS don't even come close to that. I wish it did.

Texas Jim, that 25 to 30 MPG is obtained by resetting the average miles per gallon, fuel used, and average speed AT highway speed, its not a blend, its ONLY highway. I believe you would get higher indications if your figures were purely highway. 21.5 with mixed driving at high speeds, in hot thin air, with the AC is pretty good. Try getting on the highway and resetting the parameters, Mike

[Texas Jim]

Texas Jim, that 25 to 30 MPG is obtained by resetting the average miles per gallon, fuel used, and average speed AT highway speed, its not a blend, its ONLY highway. I believe you would get higher indications if your figures were purely highway. 21.5 with mixed driving at high speeds, in hot thin air, with the AC is pretty good. Try getting on the highway and resetting the parameters, Mike

I wait till I am on the highway and reset them while it is at highway speeds. I reset it as I started to SE Tx and reset it again AFTER I had left Houston traffic and started back to Ft. Worth.

Thanks for the tip. It would be easy to forget to reset it.

I drove a rental DTS for a week .... put 1600 miles on it. It got around 25 on the highway, with me driving it pretty hard. Quite a bit faster and harder than I have been driving MINE.

If I drove mine like I drove the rental .... probably would be getting about 15 mpg <or less> instead of 20.

[Cadillac Jim]

My 1997 FSM has a troubleshooting chart on "Poor Fuel Economy." The first thing that they say is to check the codes. Gas mileage will thak a hit with a bad MAP or MAF sensor, a clogged or mis-installed air cleaner element, etc. and a DTC code will be set.

The next thing that they tell you is to do a bulletin check. For a new car, that can be a good idea, and I see that you drive a 2006 Deville Performance Sedan.

Simple things that they look for that you can fix in a few seconds are

• Is A/C ON full time, Defroster mode ON?
• Are tires at correct pressure?
• Are excessively heavy loads being carried?
• Is acceleration too much, too often?

My A/C has everything on Auto and I usually keep the temperature set for 72 F. Ocasionally a mechanic will set the temperature to 60 F, which disables the thermostat and turns the A/C and fan on high. My defroster will time out and not stay on all the time, but there may be a way to keep it on.

My door panel sticker says to use 30 psi in my tires. I use 32 for better handling. Gas mileage is fine with 30 psi but that's a minimum, and I prefer filling to 32 psi when I check the tires to make sure that it never gets below 30 psi.

Other things that are mentioned include a dirty air cleaner, vacuum hoses off or mis-routed, low coolant, exhaust restriction, PCV leaks (oil filler cap loose, etc).

It looks to me like the things to look for are a few minutes checking that everything is OK under the hood, proper A/C setting, a couple of psi above the minimum posted on the door post sticker and in the owners' manual, and a steady foot. A foot that doesn't move much can make an astonishing difference in gas mileage because every time it goes down there is a burst of gas to deal with the decrease in vacuum. You can test this by running on cruise control for a few minutes and seeing if there is much difference.

[Texas Jim]

My 1997 FSM has a troubleshooting chart on "Poor Fuel Economy." The first thing that they say is to check the codes. Gas mileage will thak a hit with a bad MAP or MAF sensor, a clogged or mis-installed air cleaner element, etc. and a DTC code will be set.

The next thing that they tell you is to do a bulletin check. For a new car, that can be a good idea, and I see that you drive a 2006 Deville Performance Sedan.

Simple things that they look for that you can fix in a few seconds are

• Is A/C ON full time, Defroster mode ON?
• Are tires at correct pressure?
• Are excessively heavy loads being carried?
• Is acceleration too much, too often?

My A/C has everything on Auto and I usually keep the temperature set for 72 F. Ocasionally a mechanic will set the temperature to 60 F, which disables the thermostat and turns the A/C and fan on high. My defroster will time out and not stay on all the time, but there may be a way to keep it on.

My door panel sticker says to use 30 psi in my tires. I use 32 for better handling. Gas mileage is fine with 30 psi but that's a minimum, and I prefer filling to 32 psi when I check the tires to make sure that it never gets below 30 psi.

Other things that are mentioned include a dirty air cleaner, vacuum hoses off or mis-routed, low coolant, exhaust restriction, PCV leaks (oil filler cap loose, etc).

It looks to me like the things to look for are a few minutes checking that everything is OK under the hood, proper A/C setting, a couple of psi above the minimum posted on the door post sticker and in the owners' manual, and a steady foot. A foot that doesn't move much can make an astonishing difference in gas mileage because every time it goes down there is a burst of gas to deal with the decrease in vacuum. You can test this by running on cruise control for a few minutes and seeing if there is much difference.

Thanks for the tips.

AC is on full time .... 100 + in Texas this time of year. "H" rated tires. 34 in front 32 in rear. I have tried it with the cruise and driving it myself. Believe it or not, I get better mileage driving it myself than if I use the cruise all time. In rolling country, I can ease up a little going uphill and let it gain speed going down the next one instead of the cruise holding it the same uphill and down.

Air filter is fine. Car is only a few months old. Shouldn't be any vacumn hoses misrouted. I have looked for any ones that may have come loose. Car runs as smooth as silk.

Reckon it just ain't meant to be that I get good mileage from this one.

So be it. I can live with it, but obviously would like it to be better.

[thu]

Texas Jim, that 25 to 30 MPG is obtained by resetting the average miles per gallon, fuel used, and average speed AT highway speed, its not a blend, its ONLY highway. I believe you would get higher indications if your figures were purely highway. 21.5 with mixed driving at high speeds, in hot thin air, with the AC is pretty good. Try getting on the highway and resetting the parameters, Mike

Yes. what I reported is the MPG across the entire tank, which includes about 10% city driving. 24-26 MPG at 80-85 MPH, 90% highway miles.

[JasonA]

Believe it or not, I get better mileage driving it myself than if I use the cruise all time. In rolling country, I can ease up a little going uphill and let it gain speed going down the next one instead of the cruise holding it the same uphill and down.

They always say to use cruise control for better mileage, but that only happens under very specific conditions. If the road is pretty flat, I might buy that. But I've found that on every car I own, cruise control worsens mileage, especially where we live and drive (rolling hills in NC and Appalachian mountains in VA). I can lose as much as 5 mpg in the Caravan using cruise control vs. controlling the gas myself.

[Ranger]

Tex,

I think the milage you are seeing is the price you pay for the 300 HP/3.71 final drive of the DTS vs the 275 HP/3.11 final drive of the DHS & standard Deville. I averaged 26 on the 930 mile trip from DFW to Northern Ill. when I purchased it 6/23. I was running 75 most of the trip (70 through Ill.)