: Better Mileage out of LD8 Northstar

07-02-10, 11:46 AM
Not too long ago I bought a 97 SLS off of my uncle after my previous car (99 Intrepid) died. That being said I went from a car that gets 26mpg/highway & 22 or 23 mpg/city to my large barge (which I love) that gets 23mpg/highway & 18mpg/city:thepan:. So what I'm wanting to know is any useful information on how to get better fuel mileage out of an LD8 Northstar.

07-02-10, 12:13 PM
That's the price you pay to drive a large, comfortable luxury sedan. You should be able to get 26 on straight highway driving (long road trips). Might check to see that your FPR is not leaking (see the Tech Tips section). Other than that, your mileage sounds about normal and about the only thing you can do that MIGHT improve it is to place an egg between your foot and the accelerator and try not to break it.

07-02-10, 10:37 PM
Other than that, your mileage sounds about normal and about the only thing you can do that MIGHT improve it is to place an egg between your foot and the accelerator and try not to break it.

Hahaha, I'm 21 with a Northstar V8 that egg wouldn't make it for 3seconds lol.

07-02-10, 10:40 PM
I understand completely. Been there.

07-02-10, 11:23 PM
Funny thing is right now I'm wanting to get gas mileage any way I can, but in the end I plan on hot rodding the car.... 21yo we want it all LOL

07-03-10, 10:28 AM
You're gonna cry when you find out there's absolutely no "hot-rodding" to be done on a 1997 SLS. What you see is what you have.......mufflers will make it noisier, but the entire exhaust system ahead of them is the problem, and when you get under the car you'll see why. No MAFs, no throttlebodies, no injectors, no magic air filters, it already has a perfect CAI.........and so on.

You have the highway package: a 275 hp engine coupled to a 3.11:1 final drive. No other gears available.

07-03-10, 12:32 PM
I'd follow Ranger's advice, I get a minimum of 26 mpg highway with my LD8. Regularly see 27-28 mpg highway, have gotten as good as 30 mpg. I don't think the roller cams in my 2000 are contributing that big a difference, but if I get silly with the gas the mpg quickly drops to the low 20s.

07-04-10, 05:26 AM
Yeah, I find that "Instant MPG" display to be handy, when I can do highway driving I get from 26-30mpg. But the accelerator is killer, I've watched it go from 26mpg to ooh about 14 or 15mpg:crybaby:... not that the drastic change has anything to do with my shoe size or age, of course:halo:. But as far as hot rodding a Northstar, I've found one company that has it down to an art, even been featured in Hot Rod Magazine. Cadillac Hot Rod Fabricators.
They ain't cheap by any means, but they know how to modify a Cadi.

07-04-10, 10:03 AM
.............the Northstars they modify can be used in Fiero kit cars and sand rails, NOT FWD Seville and Deville platforms.

CHRFAB has been discussed in here for years - they do some great work, but unfortunately it doesn't help us FWD drivers.

07-11-10, 06:54 AM
:( :( :( Well there goes that idea... but if I ever get to build a dune buggy like I want to, I have a wild idea in mind. (Partly because my father knows someone who did it). Well I guess my Northstar will have "to do". However I have found out that I can get 26-28mph at 75mph, takes some feathery peddle work but it's possible. However, I don't even wanna think about the mileage the one time I had it over 100mph :crybaby::eek:........ Good thing my father isn't on this forum:lildevil::lildevil::lildevil:

07-11-10, 10:10 AM
Damn, I wish I had gas mileage like you get! Add 3.71's to your engine and watch the mileage drop down to 22-23... :(

07-12-10, 09:15 AM
Damn, I wish I had gas mileage like you get!
Add 3.71's to your engine and watch the mileage drop down to 22-23... :(

Thats about what I get...21 to 23...depending on how heavy my right foot is. :)


07-12-10, 12:37 PM
The 2000-2003 STS, ETC and DTS, with the 3.71:1 final drive, will get 22.5 to 24.5 mpg highway on 87 octane. Perhaps 0.1 mpg more with 91/93.

The same year group SLS, ELC, and Deville Base/DHS, having a 3.11:1 final drive, will get about 24.5 to 27.5 with the same gas.

These are LONG TERM highway averages which depend on load, weather, ambient temperatures, tire inflation, and wind speeds; city driving will just about cut those figures ^^^ in half.

Magic potions may vary those mileages by .03%, but they increase the price of a tank of gas by 25%. Do the math.

07-12-10, 08:34 PM
I wind up doing a lot of city driving, but between the city and a feathery right foot (most of the time lol) I'm averaging about 21mpg overall. But if I could do mostly highway miles I could get that up to about 24-25 overall. I just use the instant MPG setting and do me best to keep the instant in the upper 20's, along with using 93octane. But with the way the motor runs, feathering that peddle take a LOT of restraint.

07-13-10, 09:47 AM
I'm happy when I'm getting 18 long term average.

I've seen 16 long term ave before.... I have no clue why though :burn: Damn Backroads!

07-14-10, 02:04 PM
97 STS

Hwy only, premium fuel, family and luggage in tow, calculating by hand miles/gallons. I have consistenly got ~26 MPG. The highest I have seen is 27 MPG. Usually running ~70mph.

Mix driving, high teens to low 20s.

07-14-10, 09:00 PM
We drove from Phoenix to Chicago last year. Averaged 26 on the way there. Ran 5mph over the limit most of the way. Averaged 25 on the way back, driving a little faster and with more junk in the car.

Until the TCC gave up we averaged 22 in suburban driving, now getting 20-21.

No matter how fast you drive be smooth on the gas and watch conditions ahead...drive the distance.

07-15-10, 07:59 AM
...drive the distance.

You can't drive the distance if you want to get anywhere here.... I bet I pass an average of 10 cars per trip home from work (~12 miles).... I refuse to follow someone going 40 in a 55..

07-12-13, 11:13 AM
chrfab does has some stuff for the fwd people it is just not little stuff its like labor intensive but there is deffinatly stuff that can be done

07-12-13, 02:26 PM
This thread is dead for 3 years. Read CHRFab's website: They specifically state that their work is not for "stock" GM vehicles. In my case labor, time, and money is no object: What do they make for my 2002 FWD transverse engine STS ? (or for your Deville ? ? ? ?)

This is a quote from the main page of the CHRFab website - they do wonderful work; just not for a daily driver................

"CHRFab does not supply parts or engines for GM factory automobiles; contact your local GM dealer."

Is there something about that statement that is hard to understand ??

07-13-13, 12:08 AM
If you want a hotrod Cadillac, get a CTS-V.

If you want a decent sleeper that is one heck of a roadtripper and can haul all your own stuff, get a FWD Cadillac Northstar V8 :sneaky:

08-09-13, 02:05 PM
i wouldn't mind taking cadillacs new twin turbo 3.6L for a spin so far it seems like it makes Ford's Eco-Boost look like junk

08-10-13, 09:00 PM
City drive 8 miles one way with about 25 traffic lights and 1/4 mile HWY I get 15.x if I am lucky.
10K trip 98% HWY and a fairly heavy foot I saw 23 mpg.
Driving 200 miles flat HWY with no traffic challenging myself to get the absolute best possible gas mileage I saw 31 mpg (average 70 mph).

Is hard for me to believe a mileage above 19 mpg in the city no matter how light the traffic would be and anything above 24mpg HWY exclusively.
I would guess a realistic overall mileage (city/HWY - maybe a bit biased towards HWY) would be 20.x mpg.