Gas consumption

[JasonA]

To be fair, even the PCM is making an estimated GUESS as to what the fuel economy is. It knows how long it COMMANDED the fuel injector to pulse open. But the PCM wouldn't detect a leaking injector. It also assumes that you have Z fuel pressure, but if your fuel pump or fuel pressure regulator is a bit off, you may not have Z fuel pressure, so the flow rate will be different.

I like using BOTH methods, and checking them against each other. If there's a big difference, you know something's wrong...either with the vehicle or with your filling methodology.

[Peter1972]

Oh my god I actually am showing 14.5 mpgs now up from 12 I guess the 30 sec warm up instead of 10-15 min is worcking.

[BodybyFisher]

I was thinking about this thread the other day, I looked at and I was getting 13.4 MPG... not good.

Then I looked and I saw that for the last 40 miles, my average speed was 26.2 Avg. MPH... ah, now the 13.4 made more sense. If your system monitors Avg. MPH, take a look at that when you judge your MPG figure, Mike

[Peter1972]

I was thinking about this thread the other day, I looked at and I was getting 13.4 MPG... not good.

Then I looked and I saw that for the last 40 miles, my average speed was 26.2 Avg. MPH... ah, now the 13.4 made more sense. If your system monitors Avg. MPH, take a look at that when you judge your MPG figure, Mike

hello, my mph avg is always low I'm almost always driving just around town. It's always anywhere from 15 to 25 Avg.

[BodybyFisher]

That is a direct reason then why you are experiencing lot gas mileage.

[95SevilleSLS]

I checked my computer last night for the average fuel economy...it was 11.8. I might as well drive my 3/4 ton suburban or my 75 eldorado with the 500. They get pretty close to that. It's pretty sad when you have 32 years of innovation and technology and a engine that is 3.6L smaller and a car that is 1200 lbs lighter can't get much over it's older predecesor. Kind of makes you want to trash it and get a older one with out the payments.

[JasonA]

I still think something may be wrong.

I routinely get 20+ mpg with my STS and my AVG MPH as indicated (I reset at every fillup) was only 28 mph last tank...which proves that most of my driving is NOT at interstate speeds.

What is your AVG MPH, and do you reset it at every tankfull?

[Peter1972]

I checked my computer last night for the average fuel economy...it was 11.8. I might as well drive my 3/4 ton suburban or my 75 eldorado with the 500. They get pretty close to that. It's pretty sad when you have 32 years of innovation and technology and a engine that is 3.6L smaller and a car that is 1200 lbs lighter can't get much over it's older predecesor. Kind of makes you want to trash it and get a older one with out the payments.

I'm driving my STS less as the gas prices go up, this summer their talking 3 dollar range again. If I could 16-17 mpg I would be tickled pink. Man 11 or 12 mile a gallon is brutal.

I still think something may be wrong.

I routinely get 20+ mpg with my STS and my AVG MPH as indicated (I reset at every fillup) was only 28 mph last tank...which proves that most of my driving is NOT at interstate speeds.

What is your AVG MPH, and do you reset it at every tankfull?

You tell me whats wrong with my STS, 20 miles a gallon. My maxima with a 3.5 V6 gets 22.1 if I could get even close to that I would be ecstatic. I refuse to belive your getting 20mpg with a 28 mph avg. theres no way thats possible lets take a vote on what other people think.

[ted tcb]

I've owned 4 STS's, and drive 99.9% city.

Avg speed is under 30mph.

My mpg is always around 12-16, never higher on all 4 cars.

Now, on the hwy, flat stretch, at 60mph, I'll get 26-28mpg.

Hilly highways, 70-80mph, and I go down to around 21-22mpg.

I've seen very little difference in the 4 cars fuel economy from the DTC.

Worse was 11mpg, dead of winter, lots of idling, 1995 STS.

My small city is made up of many small blocks with stop signs.

I never get to cruise in my normal driving cylce ... its accelerate and

brake, over and over .... I'm happy to occasionally pull mid teens.

There must be different types of average speeds ... I speed up to 40mph, then brake, and it may avg out at 28mpg. Others may actually consistantly maintain a given speed for better fuel economy ... I drive in harsh, cold conditions, and really cannot expect better than what I get.

[Peter1972]

I've owned 4 STS's, and drive 99.9% city.

Avg speed is under 30mph.

My mpg is always around 12-16, never higher on all 4 cars.

Now, on the hwy, flat stretch, at 60mph, I'll get 26-28mpg.

Hilly highways, 70-80mph, and I go down to around 21-22mpg.

I've seen very little difference in the 4 cars fuel economy from the DTC.

Worse was 11mpg, dead of winter, lots of idling, 1995 STS.

My small city is made up of many small blocks with stop signs.

I never get to cruise in my normal driving cylce ... its accelerate and

brake, over and over .... I'm happy to occasionally pull mid teens.

There must be different types of average speeds ... I speed up to 40mph, then brake, and it may avg out at 28mpg. Others may actually consistantly maintain a given speed for better fuel economy ... I drive in harsh, cold conditions, and really cannot expect better than what I get.

There you go you've owed 4 of these car and own my exact car and never have gotten over 16 driving around town. So do you agree that 20 mpg with a 28 mph avg with one of these STSs is pushing reality.

[JasonA]

Yes, Peter, I'm lying to you. I have nothing better to do with my time than lie to you about my mileage. C'mon, give me a break.

Both of my Cadillacs have given me around 20 mpg in town. If you would like, if it would feel better to you, I could take a date-stamped photo of my AVG MPG readout and my AVG MPH readout. Would that "prove" it to you?

[ted tcb]

I find it very difficult to imagine 20mpg at avg speeds of 28mph, with

that avg speed attained through stop and go city driving.

I know that Jason keeps meticulous records, so he gets the benefit of the

doubt ... either his car is a freak or the dealer swapped out the Northstar

motor with 2 hampsters and a rubber band hooked up to his front axle.

Oops ... Jason, we must have hit enter at the same time.

Obviously, I believe your mpg, but at the same time I'm jealous.

Possibly the combination of flat streets and a more temperate climate

make one helluva difference in mpg?

[JasonA]

Thanks Ted.

Well, I already took photos when I got home from work, so I guess I'll post 'em anyway. Bottom line: 19.9 mpg with an average speed of 25.4 mph. I'm only burned through about half a tank (it's actually more than a half tank, but my driveway is sloped, so the gauge is reading low), but as my commute is almost exactly the same every day, the reading is consistent through the tank.

25.4 mph:

19.9 mpg:

My drive is pretty average for suburbia. Most speed limits are 35 or 45 mph. I work 0700-1530, so my commute is somewhat off-peak. I drive the car to redline at least once every trip, but I'm also not beating on it at every stoplight either. I inflate my tires to 35 front/31 rear and meticulously keep them at that pressure. Geography here is pretty flat. Not Florida flat, but not Colorado either. Temps are in the 40s and 50s in the winter and 90s in the summer. Pretty temporate.

The overall mileage in this STS so far seems to be about 19-20 city and about 25 highway. My '97 SLS did a bit better (as one would expect). I'd usually get 20-22 city and 28-30 highway.

[BodybyFisher]

I suspect you have a pretty light foot on take offs?

[ted tcb]

Re tire pressure, I'm a tire pressure junkie, checking my tires daily through the DIC and confirming with a handheld guage.

I've tried everything from 30psi to 35 psi cold, and eventually settled on

33psi cold, all the way around.

When the tires warm up, they climb to about 36psi.

Anything higher, and I notice tar strips. Anything much lower, and the

handling seems squishy.

On my other two cars, I leave the tire pressure level up to the oil change guys.

Funny thing about these cars ... you're inspired to constantly baby and tinker with them. Even my 1971 Cutlass convertible doesn't provide me

with the same level of commitment.

[95SevilleSLS]

I've owned 4 STS's, and drive 99.9% city.

Avg speed is under 30mph.

My mpg is always around 12-16, never higher on all 4 cars.

Now, on the hwy, flat stretch, at 60mph, I'll get 26-28mpg.

Hilly highways, 70-80mph, and I go down to around 21-22mpg.

I've seen very little difference in the 4 cars fuel economy from the DTC.

Worse was 11mpg, dead of winter, lots of idling, 1995 STS.

My small city is made up of many small blocks with stop signs.

I never get to cruise in my normal driving cylce ... its accelerate and

brake, over and over .... I'm happy to occasionally pull mid teens.

There must be different types of average speeds ... I speed up to 40mph, then brake, and it may avg out at 28mpg. Others may actually consistantly maintain a given speed for better fuel economy ... I drive in harsh, cold conditions, and really cannot expect better than what I get.

We live in pretty close the same sort of town.

Just checked my average MPH and this is what I got:

12.6 MPH (I drive slow apparently)

12.0 MPG

Most of my trips consist of going to the local walmart which is 1 mile away. I no longer let my car warm up. I start it, sit for 30-60 seconds and leave and drive it nice. In that 1 mile I have a speed limit of 15, stop sign, speed limit of 25, stop sign, 40 mph stop light, 10 mph parking lot and then park. Then head home and go backwards through that. I've been going to walmart a lot on this tank and I got pissed off at a lady the other day that cut me off and redlined it so I know why I'm getting a little worse on this tank.

Yep, I reset my avg mph/mpg on every tank. I've only got 65 miles on this tank right now. So we'll see what the average goes to at the end.

[JasonA]

Just checked my average MPH and this is what I got:

12.6 MPH (I drive slow apparently)

12.0 MPG

I think that's a good indicator right there -- the MPH. An average of only 12.6 mph over 60 miles of driving means a LOT of slow stop and go.

I suspect you have a pretty light foot on take offs?

I keep up with traffic. I don't lay into it if I can't go anywhere. If I get out onto a 2-lane with no traffic, I usually let it open up. Or if someone pulls next to me at a stoplight thinking he can speed off... During the last few days, actually, I was driving it pretty hard, listening to the growl of the Northstar as I temporarily removed the PCM cover in the airbox. It was wet out today, so I got the added thrill of the tires breaking loose on the 1-2 shift at 6500 rpm.

[95SevilleSLS]

Just checked my average MPH and this is what I got:

12.6 MPH (I drive slow apparently)

12.0 MPG

I think that's a good indicator right there -- the MPH. An average of only 12.6 mph over 60 miles of driving means a LOT of slow stop and go.

I suspect you have a pretty light foot on take offs?

It still isn't that great considering I can drive the exact same way with my 3/4 ton suburban and get 10-11 MPG.

[JasonA]

It still isn't that great considering I can drive the exact same way with my 3/4 ton suburban and get 10-11 MPG.

That really does surprise me, and what prompted me to suggest that I think there may be an issue with your STS. Either that, or maybe your 'Burb is as freakishly frugal as both of my Cadillacs seem to be. Maybe your STS just happens to be on the very low end and your 'Burb just happens to be on the very upper end. Isn't your Suburban rated for not much more than 13 mpg city? Funny that you would get close to the EPA rating in one vehicle and far below it in another...with the exact same driving style and environment.

Sometimes truth is stranger than fiction...

[Texas Jim]

'06 DTS 20.1 mpg avg speed 36.2 Mix of stop and go and freeway driving in a large metro area. 390 miles since it was reset.

I get about the same on the highway, but I know why. I have a heavy foot out on the open road.

[95SevilleSLS]

It still isn't that great considering I can drive the exact same way with my 3/4 ton suburban and get 10-11 MPG.

That really does surprise me, and what prompted me to suggest that I think there may be an issue with your STS. Either that, or maybe your 'Burb is as freakishly frugal as both of my Cadillacs seem to be. Maybe your STS just happens to be on the very low end and your 'Burb just happens to be on the very upper end. Isn't your Suburban rated for not much more than 13 mpg city? Funny that you would get close to the EPA rating in one vehicle and far below it in another...with the exact same driving style and environment.

Sometimes truth is stranger than fiction...

My suburban has been very good. I have 130,000 miles on it and get 18 on the highway. You're right, it is rated for 13 in-town. If I drive it careful, like I drive the caddy, I'm sure I can get over that. I'm always trying to squeal the tires areound every corner though with that suburban. Who knows. I love my caddy though and I'm not too concerned about it. I bought it more for having a caddy and keeping the miles off of my suburban. It's a little more difficult to go in and out of traffic with a 3/4 suburban and it's a little harder to park than the caddy too.

[Peter1972]

Yes, Peter, I'm lying to you. I have nothing better to do with my time than lie to you about my mileage. C'mon, give me a break.

Both of my Cadillacs have given me around 20 mpg in town. If you would like, if it would feel better to you, I could take a date-stamped photo of my AVG MPG readout and my AVG MPH readout. Would that "prove" it to you?

Wow wait a minute I did not call you a lire just stating it's a huge differnece for having the same cars. christ sorry

Thanks Ted.

Well, I already took photos when I got home from work, so I guess I'll post 'em anyway. Bottom line: 19.9 mpg with an average speed of 25.4 mph. I'm only burned through about half a tank (it's actually more than a half tank, but my driveway is sloped, so the gauge is reading low), but as my commute is almost exactly the same every day, the reading is consistent through the tank.

25.4 mph:

19.9 mpg:

My drive is pretty average for suburbia. Most speed limits are 35 or 45 mph. I work 0700-1530, so my commute is somewhat off-peak. I drive the car to redline at least once every trip, but I'm also not beating on it at every stoplight either. I inflate my tires to 35 front/31 rear and meticulously keep them at that pressure. Geography here is pretty flat. Not Florida flat, but not Colorado either. Temps are in the 40s and 50s in the winter and 90s in the summer. Pretty temporate.

The overall mileage in this STS so far seems to be about 19-20 city and about 25 highway. My '97 SLS did a bit better (as one would expect). I'd usually get 20-22 city and 28-30 highway.

That's great that you actually took the time to take pictures . My hats off to you my comments come from me being very jealous I guess. What can I say you showed me and I'm man enough to admit it.

I've owned 4 STS's, and drive 99.9% city.

Avg speed is under 30mph.

My mpg is always around 12-16, never higher on all 4 cars.

Now, on the hwy, flat stretch, at 60mph, I'll get 26-28mpg.

Hilly highways, 70-80mph, and I go down to around 21-22mpg.

I've seen very little difference in the 4 cars fuel economy from the DTC.

Worse was 11mpg, dead of winter, lots of idling, 1995 STS.

My small city is made up of many small blocks with stop signs.

I never get to cruise in my normal driving cylce ... its accelerate and

brake, over and over .... I'm happy to occasionally pull mid teens.

There must be different types of average speeds ... I speed up to 40mph, then brake, and it may avg out at 28mpg. Others may actually consistantly maintain a given speed for better fuel economy ... I drive in harsh, cold conditions, and really cannot expect better than what I get.

We live in pretty close the same sort of town.

Just checked my average MPH and this is what I got:

12.6 MPH (I drive slow apparently)

12.0 MPG

Most of my trips consist of going to the local walmart which is 1 mile away. I no longer let my car warm up. I start it, sit for 30-60 seconds and leave and drive it nice. In that 1 mile I have a speed limit of 15, stop sign, speed limit of 25, stop sign, 40 mph stop light, 10 mph parking lot and then park. Then head home and go backwards through that. I've been going to walmart a lot on this tank and I got pissed off at a lady the other day that cut me off and redlined it so I know why I'm getting a little worse on this tank.

Yep, I reset my avg mph/mpg on every tank. I've only got 65 miles on this tank right now. So we'll see what the average goes to at the end.

My driving is pretty much the same as yours. So tell me this any ideas on why Jasons car is getting almost 20 mpg and ours are 12-14 with the same air pressure and driving habits. I', perplexed.

[ted tcb]

I think if Jason drove his car up here in Orillia on my daily cycle, his results

would be close to mine.

The town is hilly, the winter climate is very cold, the roads are loaded with

slush, lots of idling, and creeping across intersections with 6ft high snowbanks

impeding your vision.

Hopefully, my summer mileage will increase.

I'm not the least bit concerned ... I drive about 4000 miles a year, and my fuel economy is perhaps 1 or 2 mpg less than my 04 Concorde, with only

a 3.5L V6.

If my daily drive incorporated, say, 5 miles of hwy driving, my avg mpg would climb closer to 20mpg. I'm not worried because I know my car is operating correctly, I simply drive under the harshest conditions and must

pay the price.

[BodybyFisher]

I was thinking this morning, if I wanted better gas mileage I could buy a HONDA, CAMRY, TAURUS or VDUB... Then the light changed I blew by about 3 cars and I said NAH....

Anyone who is complaining about their gas mileage should drive a POS for about a month in all WEATHER (RAIN, SNOW, ETC). Don't forget to merge onto highways, do WOTs and take your family on a trip. Then get in the Caddy and do the same, then make your decision, you might appreciate it more.

Hell, if they could make a NS with MORE than one HP per CU IN and have it get 50 MPG, I guess they would.

You can't have your CAKE and EAT it also. If you can't afford the gas, its time to buy a car you can AFFORD...

If you can't run with the BIG DOGS stay the hell out of the LEFT LANE.

[caddypete]

You also need to take into consideration colder temps, I noticed you are in Mass. My Eldo losses a good 5-6 mpg in the winter compared to summer temps especially on short trips. In the summer my avg mpg is around 20.5 in mixed driving. the last 3 months or so it is between 14.8 and 16.5 mpg.