: What kind of gas mileage do you get with your Northstar?



Night Wolf
09-19-07, 03:22 PM
Just wonder.... all models, but most specifically, '94-'99 DeVille, '93-'97 Seville, '93-'02 Eldorado.

Highway mileage more then anything.... what speed? AC on? etc.... I'm interested to see what people are getting real world for highway fuel econ.

danbuc
09-19-07, 05:50 PM
CRAP...but I drive it hard. I average around 260-280miles per tank. Sometimes I get 300-320 if I'm driving on the highway a lot. Sometimes I get around 240 if I beat on it around town too much. Most I've ever gotten out of one tank of gas was 372 miles, and I was on fumes when I pulled into the gas station. That was also with near ZERO 'city' driving...all highway averaging about 70mph.

Ranger
09-19-07, 09:28 PM
right after I bought my first Northstar ('97 Deville) I made a 320 mile trip to northern Wisc. Got 30 MPG (A/C on). Have not been able to duplicate that again. I just made the same trip ('03 DHS) and averaged 27.0-27.5 (A/C on) I run to MPH. I averaged slightly less on the trip home from Texas last summer where I bought it, but I was also running 75-80 most of the way (A/C on) till I hit Illinois, that dropped my average. Here are the stats from that trip.
Fuel used - 36 Gallons
Avg. MPG - 26.3 (per the onboard computer, 25.8 by my calculation)
Avg Cruising speed - 70
Distance - 930 Miles
Total running time 13:55

Night Wolf
09-20-07, 04:40 AM
CRAP...but I drive it hard. I average around 260-280miles per tank. Sometimes I get 300-320 if I'm driving on the highway a lot. Sometimes I get around 240 if I beat on it around town too much. Most I've ever gotten out of one tank of gas was 372 miles, and I was on fumes when I pulled into the gas station. That was also with near ZERO 'city' driving...all highway averaging about 70mph.

How many gallons is your gas tank?

Cadillacboy
09-20-07, 05:04 AM
I get around 14 MPG with the AC on and driving it hard .Nailing the pedal a few times and distance is 30 miles .I can even get 22 MPG for the same distance w/o driving it so hard with A/C on (staeady speed 60 mph). However, I don't like it driving like a grandpa because I just wanna hear the sound of the engine from 2500 RPM and up but this does nothing but hurts the fuel economy lol

clarkz71
09-20-07, 06:54 AM
I avereage 23 mpg city/highway. I get 460 miles out of a tank
without running out. I once got 480 but it took 20 gallons so
another few miles and I would have run out.

I recently made a road trip of about 700 miles each way. Driving
70 - 80 mph, air on, I was averaging 27 mpg. 1400 miles total
and didn't use a drop of oil.

Submariner409
09-20-07, 10:14 AM
18.5 gallon tank, 93 octane Texaco fillup once in a while, but mostly 87. Around town and local, about 18-19 mpg. Mixture of local/highway, 21-23. Long highway/Interstate (to Florida) at 60-75 mph, 25-26. 34 miles, flat road, at exactly 55 mph gave 28.6 mpg. 99% of all that is on the east coast at sea level. 1 quart of Pennzoil 5W-30 Platinum in ~3,500 miles.

ejguillot
09-20-07, 04:34 PM
My STS:

City? 18mpg, worse if i'm letting the N* sing (which I do often).
Steady state 55mph: Have seen anywhere from 28-34mpg instant, depending on whether the a/c is running (running AC knocks down economy about 10%), road surface, and winds:
Steady state 80mph: From 22-27mpg, same conditions as above.

Over the whole tank: With only city, a little under 18mpg. Better if highway is mixed in.

danbuc
09-20-07, 06:06 PM
How many gallons is your gas tank?

Same as any other 98-04 Seville....around 18 somethin' gallons. My car runs rich though and I haven't figured out why yet. It passed inspection with flying colors....even though the exhaust smells like fuel. Who knows. Most I every average on the highway is around 24.5mpg or so. It's very hard for me to drive the car in a civilized manner. Mostly because I don't really care about fuel economy. If I did, I wouldn't be driving a 4000lb with a V8 now would I...:rolleyes:

Mexicano Leon
09-20-07, 07:26 PM
97 Deville 10.7 miles per gallon {premium

Submariner409
09-20-07, 08:47 PM
????? 10.7 mpg? Do you sit around Taco Bell in P with the A/C on all afternoon??? If that mpg is true, you never get over 25 mph and have problems. Otherwise, chuckles and grins........

Shaggy
09-20-07, 11:04 PM
Usually ~28-29 mpg. I have never noticed any difference with the AC on or off.

smooththg6969
09-22-07, 03:05 PM
i was getting 13.5 mpg with my 99 seville changed the o2 sensors even though I didnt have any codes. and now I average around 17 mpg with city and high way mixed I average around 15 just with just city driving. but then again I do like to hear the sound of my magnaflows. ps. i also have about 100lbs of audio equiptment in the trunk.

greg-sls
09-23-07, 11:35 AM
The best I've done for city driving (in Phoenix) is 17 mpg - and that's based on the avg mpg on the DIC. Of course, the A/C is on most of the year, but in early spring when conditions are perfect, I can do a bit better - and that is driving like there is an egg between my foot and the pedal. On road trips (thru the desert and in flat areas), I've gotten as good as 26 mpg averaging 75 mph. Once in the mountians - not so good.
97 Seville SLS
Danbuc: check your FPR - it's an easy fix and will cause you car to run rich

fubar569
09-23-07, 02:14 PM
city: 15-20mpg

highway: 26-32mpg

93 octane only - 97 deville
modded airbox
no TC
no cat
custom Dual 2.5" catback

Murphyg
09-23-07, 03:31 PM
Would be good to know if these are Inst MPG or Avg MPG.
It really does make a difference.

01 STS I average 19 mpg. Thats mostly highway. Id say 70%. And thats clear highway as well. Not this stop and go bumper to bumper rush hour nightmare. At an average highway speed of 80 mph. The rest of my driving is city between 30 and 50 mph.

fubar569
09-23-07, 03:55 PM
Would be good to know if these are Inst MPG or Avg MPG.
It really does make a difference.

01 STS I average 19 mpg. Thats mostly highway. Id say 70%. And thats clear highway as well. Not this stop and go bumper to bumper rush hour nightmare. At an average highway speed of 80 mph. The rest of my driving is city between 30 and 50 mph.

averages...over multiple tanks...all on 93 only

i do drive 55-65mph compared to you speed racers at 80 though :D

that seems to be the key...anything over that speed and economy drops like a rock...

and strangely my mods did net me a slight bump in mileage...about 1-2mpg

Murphyg
09-23-07, 04:14 PM
In my 93 SLS with the 4.9 Litre I was getting round 17.5-18 under the same driving as I stated above. Didnt matter if ac was on or not. Was still the same. Also I had to use premium fuel in that engine. Do seem to get a little bit higher though depending on the outside temp. In the 93 there were always a few weeks in the summer when it wasnt stifling hot that it would get round 19.5.
Maybe just a coincidence but get a tiny bit beter in the 01 as well when the temp is just right. Not too hot and not too humid.

clarkz71
09-23-07, 04:38 PM
Would be good to know if these are Inst MPG or Avg MPG.
It really does make a difference.

.

All of mine are average. 23 city/hwy 27 @ 70 to 80 with a/c on hwy.

wydopnthrtl
09-25-07, 02:00 PM
We are pretty mixed with our 01 eldo. My wife does around town stuff 50% of the milage.. she gets about 18-20. But we do drive about 180miles every week out on the freeway at 70mph. So I average about 24 overall year round.

This last may we went to Memphis and got a solid 26mpg using 87 octane in the way down. And 29mpg running 93octane on the way home.

If a few weeks we are driving from Mich to Fla and back. I'll report my milage when we get back.

Rich

fubar569
09-25-07, 05:41 PM
We are pretty mixed with our 01 eldo. My wife does around town stuff 50% of the milage.. she gets about 18-20. But we do drive about 180miles every week out on the freeway at 70mph. So I average about 24 overall year round.

This last may we went to Memphis and got a solid 26mpg using 87 octane in the way down. And 29mpg running 93octane on the way home.

If a few weeks we are driving from Mich to Fla and back. I'll report my milage when we get back.

Rich

keep the bottle full and hit the drags while you're there! :worship:

wydopnthrtl
09-26-07, 01:51 PM
Not while on the road. But as soon as I get back I will make one more outting before they close the tracks.

Rich ;)

boricuacaddy
09-26-07, 02:45 PM
I get on my 97 SLS around 15 avg. Just city driving stop and go traffic. Too many slow pokes around my area!

David

coolbeans
09-27-07, 04:42 PM
With my '04 DeVille, dash reads 25.2 av., last 2 interstate runs I filled the tank to where I could see the gas, (I did this on two round trip runs), hand calculated, I got 27.3, and 27.2 mpg. using 91oct.This is at 77mph, cruise set,AC on, I-80 is hilly, 6700 elv.

iroc86
10-01-07, 12:58 AM
I took a 160-mile trip a couple months ago and averaged 28.3 mpg in my '98 ETC. This was on rural country roads, where the speed fluctuated between 45 and 60 mph. A/C was on. I don't usually do a lot of highway driving.

For everyday stuff, I get anywhere between 18 and 21 mpg. That includes a few trips each week into Pittsburgh during rush hour (ugh!).

The most important thing I've found is to make sure you're burning the right fuel. And by that, I mean Shell. My Eldo picked up 2 mpg the instant I put their V-Power in the tank, and it's been like that ever since. (No, it's not a hallucination ;)) The extra detergents and additives really seem to help. If I had used it a few months ago on my trip, I'm sure I would have broken the magic "30."

tankaillc
10-09-07, 02:14 AM
With my lead foot(and my 1st car being a ford escort) I'm on the bad side of this best for me is 18 mpg city/highway but it hangs at 14 for me but hell i'm happy seeing that my brougham is maybe getting 6 or 8 mpg been working in that problem and just haven't kicked it but i need to having to fill the 25 gallon tank makes you think.

Drparj
10-09-07, 04:29 AM
I get about 19-21mpg average. Have been keeping track of the last few tanks. get around 370miles to the 18.5 tank. thats a mix of highway/street with that being 70% highway. AC off. Only a few times I pegged the gas to pass. Mostly just easy going around 75mph

AnthonyCasta
10-12-07, 11:00 AM
The best I've done now is 30.4 Avg, steady 80 - 85 MPH Cruise set with A/C on ... Straight streach of hwy. Using 76 or Mobil gas regular 87

shawn93poloconv
10-12-07, 07:27 PM
I'm averaging about 26-27 on the highway. Cruise on 77+ MPH in the Carolina foothills. I think that's pretty good considering my 93 Vette gets 20 if I take it easy.

MisterBlue
10-12-07, 07:33 PM
My old '98 STS never got less that 30 on the highway. After it got well broken in (30k mi), i got 32-34 mpg on the highway...consistently. Got 32 mpg on a 750 mile trip (one stop for gas), and then made the run back home and hit 34 mpg. That was running on cruise at 67-73 mph. I wouldn't have believed it myself, but I topped the tank and did the old "divide miles traveled by gallons used" to verify. (The mileage computer is very accurate, by the way...never off by more than .2-.3 mpg.) City and local was another story, usually 16-19 (but then again, I raced everything I pulled beside, except Corvettes). These are heavy cars; hills, low tire pressures, "fat" tires, cheap gas, and open windows or sunroof will all chop miles off what might you get. (Oh yeah, so does driving with your foot on the brake, as about 1/3 of the drivers around here seem to do.)

I always used prem. gas, always kept tires at 35 psi, and always drove w/air on.

My DHS doesn't do nearly as well on the highway, but it's still pretty low miles and it sits at least an inch-and-a-half higher (and that makes a big difference above 50 mph). I'm averaging 27-28 now, and feel that'll improve as the engine gets well broken in.

wydopnthrtl
10-13-07, 10:13 AM
Just got home last night from our Mich -to- Fla trip.

Stats:
Drove 2,983 miles
840lbs worth of people and luggage (4 people and the trunk PACKED)
Just changed oil before trip (10w-30 mobil 1 full synthetic)
Tires set at 35psi (cold)
Temps = 90s for first 75% of trip. 60s for the last 25% (AC on)
Speeds = 70-72mph (cruise on most of the time)
Approx 250 miles were city stop and go driving in 90F temps
Oil level appears to be identical as when we left. A bit darker but not black at all.
Gasoline = Shell 93octane "V-Power" for 4 tanks. (5 tanks used on trip)

Quick notes on milage:
The sweet spot for "instant milage" when driving on flat ground is 68-69mph. I can hold it on a steady 31-32mpg w/cruise on. Up it to 70-73mph and it'll drop into the 29-30 range.
Mountians/hills.. Cruise on and it'll drop to 12-13mpg going up hills. Turn the cruise off, accelerate 5mph on the down slope, and holding the throttle steady going up the next hill will drop the instant mpg reading to 22mpg and drop you back to the speed you started off with. (70mph in my case)
Traveling through Mich, Ohio, Ky, Tenn, Ga, Fla, Ala, Ky, Oh, and back to Mich. I DEFINATELY got the best milage in Ohio. The roads in Ohio are smooth and flat for the most part. Driving at a steady 67mph I was able to see it hold 34mpg when on the dead flats where no traffic made me slow or speed up.
Cheapest gas was in KY = $2.57
Most expensive was Mich = $3.10
Worst / most rude drivers = Mich
Best / most curtious drivers = Alabama
Best roads = Ky & Ohio
Worst roads = Michigan

This Eldo is rapidly become one of my favorite cars that I've ever owned! It's comfortable, is cheap (when bought used), has room for 4 adults, and on nitrous can bust 13s on the dragstrip! http://www.racetested.com/images/gallery/01_Cadillac/2001_Cadillac.html


Here are some pics taken right off the cars display.

http://home.comcast.net/~rbickford325611mi/images/Caddy/Milage-results.JPG




I really like this car...

http://www.racetested.com/images/gallery/01_Cadillac/2001_CadETC_Extl.jpg

jfreezn
10-15-07, 12:09 PM
Just wonder.... all models, but most specifically, '94-'99 DeVille, '93-'97 Seville, '93-'02 Eldorado.

Highway mileage more then anything.... what speed? AC on? etc.... I'm interested to see what people are getting real world for highway fuel econ.

94 ETC with Northstar and 3.71 gears:
In June, we made a trip to Reno to bowl in the Nationals, About 1700 miles, round trip from Phoenix. Two passengers, 6 bowling balls, light luggage, and a cooler. AC always on, ambient reaching 100 plus degrees each day, altitude varied but mostly over 3000 feet. I kept very accurate consumption records and we average 22.1 MPG for the entire trip, traveling at speeds somewhat above the posted limits. Infrequent two lane passing would require 95 on occasion. The dash display confirmed my mileage calcs. and my Magellen GPS verified our speed and altitude.

Bowling results--don't ask!

Jim in Phoenix

cadillac8686
10-15-07, 02:11 PM
I get 24 mpg avg every day on the way to work and 23 mpg on the way home. I go an average of 65 - 70 mph.

cadillac8686
10-15-07, 02:13 PM
With the a/c on it's shitty, no power no milage Why? Everyone elese I see that runs the a/c gets good/better milage!

Tommy Deville
10-17-07, 01:44 AM
the best I've ever done is 24.5 MPH 215 mile trip, going up hills average speed was 80.

taking a trip up tp Boston this weekend 234 miles to the 1st destination, I will report my findings.

Murphyg
10-19-07, 05:34 PM
With the a/c on it's shitty, no power no milage Why? Everyone elese I see that runs the a/c gets good/better milage!

Read here somewhere that with the AC on you should have the fan set to recirculate the Cabin Air.

Ranger
10-19-07, 07:39 PM
Recirc is just for max cooling.

Submariner409
10-19-07, 08:39 PM
A/C is a significant load on a fairly small engine. Using the recirc feature will take a bit of the interior cooling load off. Don't forget that you're not only driving an A/C compressor, but also supplying the necessary increased electrical loads.....engine cooling fans, A/C clutch, blower(s), etc.

IF you floor it, the PCM senses WOT and shuts down the whole A/C system until rpm and loads are back in safe limits. Tooling around town or near suburban you're moving a 2 ton car and running your private HVAC system.

iroc86
10-20-07, 11:23 AM
I'm not trying to get off-topic with a discussion of air conditioning systems, but...

According to the service manual for my '98 ETC, air is always recirculated when the climate control is set to 60 degF. (This is identical to "MAX A/C" as seen in other vehicles.) In any other setting, the computer automatically regulates when recirculation is used. Unfortunately, the manual does not describe the criteria for recirculating the air.

So, pressing the recirc button obviously forces that mode, but it's possible the AC system was already in that mode thanks to the PCM. I always thought it would be nice if the recirc light illuminated to let the driver know what's going on.

Like submariner said, air recirculation (i.e. "MAX A/C") is a good way to retain some efficiency. On other cars, such as my old Jeep Cherokee, I turned it on as soon as possible. (It's more efficient because the system only has to remove heat from the cabin air, which is presumably colder than the outside temperature.) On the Cadillac, I just let the system do what it wants. I have faith in the GM engineers :)

Submariner409
10-20-07, 12:01 PM
Yeah, that ^^. The only reason I tacked off on the A/C thing in a gas mileage thread was to call attention that A/C is a pretty significant load on the engine and can really affect gas mileage.......perhaps not quite so much on the open highway as in town, but still a factor.

If we all lived at the same altitude, with the same temperatures, flat roads, humidity, new tires, no mountains, same brand/grade of gas, no idling or stops, then a mpg or two difference in examples of the same vehicle would be relevant. As is, comparisons are pretty iffy..............

(In my STS, in order to hear an airflow change with recirc, I have to run the blower in high and listen for the noise level change, otherwise you can't tell.)

Tommy Deville
10-21-07, 07:38 PM
ok, just returned from my trip, it was 536 miles round trip average spped of 78.3 MPH 99% highway, spent about an hour in stop & go traffic, A/C on, no WOT's i averaged 22.5 MPG's Car ran great!

my city driving is aslow as 10MPG & AS HIGH as 13.5 MPG with mixed driving, any tips? I just read some1 changed there o2 sensors just because he wanted to, is that a place to start?

limoguy
10-22-07, 08:03 AM
;)98 cady deville northstar. I get between 23-24 mpg. its got 120k miles on it

krimson_cardnal
10-24-07, 03:45 PM
Clean the TB. You might be surprised by that.

I'm a believer in SHELL fuels to reduce engine "gunk". A 1200m run on their premium will clean thing up a bit. You can "off the shelf" the same thing. K_C

limoguy
10-25-07, 09:39 PM
:stirpot:Shell is in the top tier catogory. I been using 87 octane, whatever brand is lowest..she is running fine

dano2407
12-13-07, 11:22 AM
97 deville 14.5 to 15 mpg in the city. Thats driving about 8-10 minutes to work and from work. Usually speeds from 50-65.

Murphyg
12-18-07, 08:01 PM
Am now down to 17.9 from 20 avg mpg in my 01.
Am sure it has to do with the cold and all the white crap we've had to plow through this week.

Chances are has the original plugs too. At about 50,000 miles on a 7 year old vehicle, Still think its time for a change. Wires too.

Should also add that I dont seem to receive any significantly more mileage when changing from 87 to a higher octane. Not even 1 mpg.

Cadillacattack
03-20-08, 05:01 PM
It florida here it's flat roads. On Hwy at 70 mph with no stopping I get 25 to 26.7 mph on my 96 deville V8. In city it varies up to 17 mph. Otherwise it sips fuel nicely on the open road. 2 gallons is usually all she burns in 58 to 60 miles.

NAFTA
03-21-08, 02:14 AM
95 Cadillac ETC:
Heavy driving conditions in the city 8-14 MPG on the gas when I'm in a hurry, when I'm cruising lights about 11 - 18 MPG.
Highway driving like NASCAR 90 MP/H+ 8 MPG, doing steady 70 - 80 MP/H cruising 24 - 29 MPG
This is on half way of engine oil life at 101K miles. Need to change my spark plugs soon and change the oil even though I still have a 1500 miles on it, it's been a rough winter.

Murphyg
03-21-08, 02:35 AM
It is a 95 though. eh ?...

LOL

Take care of it. And you may be surprised. Or it may be too late....And that would be too bad......

Is a shame.

tateos
03-21-08, 12:43 PM
Around 22-25 MPG taking it easy driving to and from work - around 10 miles stop and go, and 20 miles highway 65-70 MPH. Around 26 on a trip 75 MPH. Maybe around 18 MPG around town - even less if not driving gently.

johnnyw
03-21-08, 01:14 PM
If I use the cruse control on my '99 Deville I can easilly get 30 hwy at 70 mph. Mix in some intown driving and it drops like a rock. Day in and out I usually average 22 or 23 mpg. My co-workers find it hard to believe that the DeVille will get 30. The key is consistency.

94cady4.6eldo
03-23-08, 09:32 PM
I have a 1994 eldorado 270hp base with 90,000, aftermarket mufflers ,coils and intake and I only get about 15 miles per gallon. The most its ever got was just over 17 miles per gallon .I just got the car a month ago and did the mods .and have only had it on the highway for a few miles hope it gets better.My foot is in it haph the time.ran 14.7 at atco raceway spun bad anyone else run 1/4 mile.

Submariner409
03-23-08, 10:08 PM
94...........Your car should get around 13 - 18 in and around town, 17 - 20 suburban, and 23 - 28 long highway. You didn't need coils, and there's a chance that, if you went overboard on the intake air, you gave up some low and midrange throttle response (which is where the engine runs 99.99% of the time....).

If you haven't already done it, invest in a set of 41-950 ACDelco plugs, set .050", and a set of ACDelco plug wires. Don't go to aftermarket plugs and wires. Far too many posts on the subject, but read and heed.

94cady4.6eldo
03-23-08, 11:51 PM
yea I put the ac delco plugs in when I did the coils.I run a parts store slapped whatever I could find on it. I will keep the stock wires good idea.

94cady4.6eldo
03-23-08, 11:56 PM
Shes old but runs good some of my customers tell me 94 95 northstar motors dont have as many head gasket issues.Only 90,000 miles paid 2900 for it looks like granny owned it.Very good condition.

limoguy
03-25-08, 09:50 AM
98 deville..152k....I usually get about 22MPG average, I mostly do highway. No complaints

tateos
03-25-08, 01:46 PM
94cady4.6eldo:

I think I read the '96-'99 engines were the worst for HGs

indianavince
09-02-08, 10:32 AM
2000 STS... just shy of 100k, drove a 1115 mile round trip from Lafayette, IN to KS City. According to the computer I averaged 64 mph (75mph cuising) and the fuel mileage was a solid 32mpg. This car rocks on the highway.
AC always blowin, steady smooth driving.. brisk highway entries to blow the valves clean, I have fun, but settle into the "flow" on the highway usually hanging with the same couple trucks for 50-100 miles. (my car uses a quart of Castrol 5-30 every 2000 miles or so.) I get about 18mpg around town... funny that milage is about the same as my Olds Alero that was totaled before I bought this used Caddy. The Olds would do 34 on the highway (it was a 3400 V6).

Submariner409
09-02-08, 12:01 PM
A 2000 STS (3.71 final drive, 2350 rpm at ~70) getting 32 mpg long highway is nothing short of incredible. All flat land ? What octane ? What gas ?

(Best I have ever done in my '02 is 27 mpg, computer and miles/gallons, alone and no load for 385 miles.)

The oil mileage is about perfect.......many Northstars get less, some get more.

wachuku
09-03-08, 01:21 AM
'97 STS. 120K.

Yet another long road trip with the same results: average speed > 70 MPH (barely). Mileage > 25 MPG each way (barely). The best I ever got was 27 MPG; in that trip though I had a slightly lower average speed and I didn't bring the car up to 100+ during passing like I often do, which can't be good for mileage.

I think oil is 1 quart per 750 to 1000 miles; I need to keep better tabs on that.

City is 18-20 MPG with lots of stop-and-go.

STSj90
09-03-08, 03:38 AM
I got 27.7 on the highway being very easy on the throttle. At around 65-70....Even around 55-60 the same deal. Just have to be Soft with the pedal. Setting the Cruise isnt the best thing for gas milage. My foot is better for that.

In the city with my foot in it hard ALOT i get around 18.9 MPG.

These cars arent bad with gas milage. Love the POWER! Shoot, Screw the gas milage. I could care less! All i need it that V8 sound and power! Good gas milage isnt a bad thing tho.

thu
09-03-08, 02:34 PM
Driving constant 75-80 mph, I get 25-26 (hand calculation) in my 2003 STS.

indianavince
09-04-08, 11:24 PM
A 2000 STS (3.71 final drive, 2350 rpm at ~70) getting 32 mpg long highway is nothing short of incredible. All flat land ? What octane ? What gas ?

(Best I have ever done in my '02 is 27 mpg, computer and miles/gallons, alone and no load for 385 miles.)

The oil mileage is about perfect.......many Northstars get less, some get more.

---My final drive must be different... Mine pulls 2000 rpm at 72mph.
I double checked the math and gas reciepts on a trip from Indiana to Cleveland in 18 degree weather it was 33 mpg-- all highway(no city).

I must be an easy driver as I used to get 34mpg out of a 6 cyl Alero and 45mpg out of a 1989 VW golf with 5 speed.---these are highway fugures.

I know someone is asking tires??? Tire pressure??? Michelin Hydro-edge (stock size), and about 32 psi.

indianavince
09-04-08, 11:32 PM
PS you STS guys need to realize I have the SLS... the engine chip is different (and from an STS post the final drive is higher (or long legged) with the SLS-which I have). The SLS engine is tuned for less HP and more torque. Look in the specifications of your owner's manuals. Glad I got the SLS.... the ride is a bit softer too

Also while my latest MPG feat of 1115 miles at 32mpg, this is not isolated. Two trips to Chicago from Lafayette, IN with city driving mixed in got me a two tank average of 27mpg even sitting in stopped traffic on the "tri-state" (Yes AC was on).. I do make sure tire pressure is up... I have one rim that is a leaker (2-5 psi a week)..

I had new plugs (stock AC Delco) installed at 78,000 when the front coil pack died.

Submariner409
09-05-08, 08:08 AM
indiana, In the opening to your post #58 you clearly state that you have an STS. Thus the inquiries about gas mileage. It is common knowledge that an SLS or base Eldorado with the 3.11 final will get 27 - 30 mpg on the road.

gary88
09-05-08, 07:31 PM
On my SLS I get about 15.9mpg around the city (up to 17 if I'm really conservative on the pedal). On the highway I easily get between 26-29mpg.

97Concours1
09-05-08, 11:40 PM
1997 Deville Concours with 105k miles:

The best I've ever gotten was about 27.5 mpg highway and 21 mpg city. I guess the Concours has the STS cams and final drive ratio so maybe that's the best that I can expect. I've thought about getting a smaller economy car, but there arn't many of reasonable size that get any better mileage. Even with $4 gallon gas I kick it in the butt and rev it to redline once in a while to keep it cleaned out. WOT kick downs from 25 mph are the most fun, but it puts a little dent in the average mpg number.

Submariner409
09-06-08, 12:43 PM
97, If your VIN has a "9" as the eighth digit, it's the 300 hp/3.71 HO option Northstar. If the digit is a "Y", you have the 275 hp/3.11 engine. (The 97 may be a bit off the hp figures, but same idea applies......)

If you get 27.5 mpg, road, chances are that yours is a VIN "Y".

foos
09-06-08, 11:05 PM
('99 STS)

80MPH constant, florida weather, I get 22-23MPG. 55-60mph i get 25-27mph.. and sometimes I can get close to 30 if I go 45-55mph range and it's really cool (for Florida anyway lol)..
Ciry driving 14-16mpg but I am really not light on the pedal!! :)

Man I would love to get 27-30 mpg going 80 :/

indianavince
09-07-08, 02:04 PM
indiana, In the opening to your post #58 you clearly state that you have an STS. Thus the inquiries about gas mileage. It is common knowledge that an SLS or base Eldorado with the 3.11 final will get 27 - 30 mpg on the road.

OOPS sorry about the typo... and I'll keep quite then.

indianavince
09-07-08, 02:08 PM
('99 STS)

80MPH constant, florida weather, I get 22-23MPG. 55-60mph i get 25-27mph.. and sometimes I can get close to 30 if I go 45-55mph range and it's really cool (for Florida anyway lol)..
Ciry driving 14-16mpg but I am really not light on the pedal!! :)

Man I would love to get 27-30 mpg going 80 :/

Bummer GM didn't but in a 5 speed auto with much lower final drive for the STS. Funny to think the high-po STS probably has a lower terminal speed than the SLS. I figure the SLS is only pulling 4000-4500 rpm at 140mph. Are both cars limited to 152? Not that I would ever try in the USA. I did do a 110 mph shakedown/testdrive, but I got it back below 100 then below 80 in short order on a flat piece of interstate. I haven't seen 85 since.

foos
09-07-08, 02:15 PM
I don't remember offhand what the rom is ar 80 but i think it's about 2500..
My cutoff is 135mph(somewhere close to that anyway).. I uhh.. Know this by experience..
I don't understand why they just didn't change the 4th gear to be a closer ratio in the tranny, unless it's already close and it's the final drive gear that is the culprit :)

STSj90
09-08-08, 08:21 AM
Well, at 135mph my STS shifts and pulls hard, hits RPM around 4000-4500 rpm... After it shifted i stopped looking and only looked at the speedo right after that and i was doing over 145. Scary looking. But feels like your floating on clouds. Its pretty awsome. Feels good. BUT, Ive been alittle scared to try it again.

Submariner409
09-08-08, 09:28 AM
STSj90......Take a look at the tire specification sticker on your driver's door. That will give you the size and speed rating of the OEM tires and therefore the setting of the speed limiter: S is 112 mph, H is 130 or so, while W or Z is up around 154 or no limiter. If that is missing, the RPO sticker under the spare tire cover will tell you: enter the codes in www.cadillacfaq.com//rpo/index.php .

Someone else will know: Were ANY SLS's delivered with limiters above 112 mph, or did they all come with S tires as OEM ???

If you have a Z car and lesser rated tires, any speed over the rating of the tires currently mounted on the car is flat dangerous.

All the Sevilles might make it to 148 - 158, but after that there's not enough HP, too much car, and too much wind resistance to go any faster.

STSj90
09-08-08, 09:38 AM
STSj90......Take a look at the tire specification sticker on your driver's door. That will give you the size and speed rating of the OEM tires and therefore the setting of the speed limiter: S is 112 mph, H is 130 or so, while W or Z is up around 154 or no limiter. If that is missing, the RPO sticker under the spare tire cover will tell you: enter the codes in www.cadillacfaq.com//rpo/index.php .

If you have a Z car and lesser rated tires, any speed over the rating of the tires currently mounted on the car is flat dangerous.

All the Sevilles might make it to 148 - 158, but after that there's not enough HP, too much car, and too much wind resistance to go any faster.

The sticker says Z rated. I beleive the tires on my car are z rated. There made by yokohama. But i better check them out and make for sure that there z rated before i do anymore speed runs. Thanks for reminding me!

smooththg6969
09-08-08, 06:59 PM
well i get up to 140 with no problems in my sls did this one time at about 3 in the morning there was a base cts trying to keep up but i flew pass him like he was standing still. weird i here these cars max out at round 140 but the car felt like it could pull to 165 and was still pulling at 140. my door sticker says s rated. but then again i have AJ's tune

Submariner409
09-09-08, 08:01 AM
AJ and a couple of others can remove the electronic speed limiter code from the later FWD Northstar OBD-II PCM's.

Hope you have Z tires..........:lildevil:

buickboy1972
01-26-14, 07:03 PM
My fuel mileage is down about 4 mpg because of my winter tires and road conditions at the moment. Was just wondering what other Cadillac's are running. This was only a 25 minute drive but I average 22 to 24 mpg combined city highway in the winter and around 24 to 27 combined in the summer with my summer tires on. This is my 98 Deville. The service engine light is from my knock sensor that I am afraid of changing because its under the plenum.


180521180529180537

knotgoalie
01-26-14, 07:13 PM
Sounds normal to me. I was clocking 27~28mpg in warm weather and currently 19~20mpg in mostly -15~-20c...90% hwy driving.


J.R.

rodnok01
01-26-14, 08:34 PM
That's a out what I get from both mine. Knock sensor should be easy just take intake off. Never heard one go bad on these forums. I would look at the wire.

Ranger
01-26-14, 08:46 PM
I was pretty sure we've done this before.




We have.
http://www.cadillacforums.com/forums/northstar-engines-system-technical-discussion/117892-what-kind-gas-mileage-do-you.html

buickboy1972
01-26-14, 08:56 PM
Nice. I hadn't noticed that post. Probably due to the fact the last post was almost 6 years ago on it. Hell of a good memory on you :thumbsup:

Ranger
01-26-14, 09:11 PM
I've been here a while. :)

Submariner409
01-27-14, 08:30 AM
Posts moved to the gas mileage thread in Engines: Northstar.