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I have a 1992 Sedan Deville with the 4.9L engine and I'm averaging 13.4 MPG. The car is rated at 16 city and 25 highway. It seems to be too low. I always use premium fuel as recommended. Does this seem typical for anyone else? Please share your fuel economy and recommendations to improve it.
:hmm:
 

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Big_Cadillacs said:
I have a 1992 Sedan Deville with the 4.9L engine and I'm averaging 13.4 MPG. The car is rated at 16 city and 25 highway. It seems to be too low. I always use premium fuel as recommended. Does this seem typical for anyone else? Please share your fuel economy and recommendations to improve it.
:hmm:
All depends on a driving pattern. Idling, short trips with cold engine can easily bring the average fuel economy down to your figure. Take a short highway trip at say, 65 MPH with average fuel economy reset. It will give you something to compare with.
 

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1992 Town Car Cartier & 2014 Accord LX MTX
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That sounds about right. I also have a 92 Sedan deVille. In winter, I get about 14.4 mpg with all the idling I have it do to get it warm in the morning, plus I don't go on a lot of long trips. In summer I get about 16-17. It doesn't idle around nearly as much in summer, and i generally tend to drive longer distances because it isnt cold. And crusing around aimlessly is fun in summer time.

My car has 113700 miles, I've had it since 99,098 miles. I drive it kind of hard sometimes, I will accelerate fast sometimes just to keep the car in top condition, and I like to feel the 4.9's torque pin me against my seat in 1st gear. Lately It has been feeling a bit quicker due to the 20* ambient temperatures. I bet this is what it would feel like in summer time if I put that Cold air Intake on it.

Big_Cadillacs, tell me about your deville, what color combo is it? Does it have leather or cloth, what does it have for options?
 

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01 frontier , 89 Shelby CSX vnt
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13 is the best i got dureing a breif time that my car saw solid city driving in havey traffic ....

before the main bearing job i was getting around 20.1 , im very curious as to what it will do now
 

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2018 Mazda 6 (Venus) 1964 Impala (Betty) 1991 Miata (Dolly)
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My 91 DeVille with 206K averages around 17-18 most of the time on the Fuel Data Center. My commute to work is a little over 20 miles, most of it on a two-lane highway. If there are no pokey people ahead of me, I can cruise at 65, but most days I stuck at 60 or below.

On a 500-mile trip to a friends wedding in September, the only long drive I've taken with the car, I got a little over 20 on the drive out, but only 16 on the return due to a strong headwind. Still not bad considering I was doing 70+ and the DeVille is basically a chromed brick aerodynamically.
 

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1992 Town Car Cartier & 2014 Accord LX MTX
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I get 21mpg at a constant 75mph
 

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I~LUV~Caddys8792 said:
I get 21mpg at a constant 75mph
Well it's a little bit low. How are you tires? Pressure? Last summer I made a 70 miles mostly highway roundtrip with ups and downs. It averaged 28.5 MPG and 27.1 MPG accordingly. Never had similar experience before or after... Usually on long highway trips it is between 23 and 26. I use 89 octane and timing is set at 8. Rotella 15W-40 year around. Tires - 32 psi front, 30 psi rear.
 

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It was at 35PSI front, 32 Rear, I had cruise control on most of the time, running on 90 or 91 octane with Rotella 15W40 oil. I did plugs about 4 months prior, overall it was in damn good running condition.
 

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1992 Cadillac Sedan Deville
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My 1992 Deville is getting about 9 MPG in the city and 24 MPG on the Highway. I don't use overdrive in the city because I was told that its harder on the transmission (shortens its life), probably that is why I get such a low MPG in the city. Has anyone else heard about O/D Shortening the life of the transmission when used in the city?
 

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78 FWB d'Elegance, 92 deVille, 93 Seville, 06 DTS
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After reading all of this I feel damn fortunate, in my seville (4.9) i average out somewhere between 18.9 and 22.8 for my daily commute (which is about 120 miles round trip in LA traffic....sometimes 85, sometimes 8.5:yup: )
We also do at least 1 road trip a month and at 70 it will settle in at around 25~26, and holding 90 will yield in the neighborhood of 19~20.

I always run chevron or shell 91, and although I have heard several people say octane is irrelivant, I had the timing retarded so I can run 87, however after repeated testing, mysteriously 91 seems to add somewher between 1.5~2.5 MGP regardless of winter or summer (like us LA people know what winter is)
T
 

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SilverFleetwood85 said:
My 1992 Deville is getting about 9 MPG in the city and 24 MPG on the Highway. I don't use overdrive in the city because I was told that its harder on the transmission (shortens its life), probably that is why I get such a low MPG in the city. Has anyone else heard about O/D Shortening the life of the transmission when used in the city?
I Have not heard of that, It seems as if you you are doing more harm than good, while I am no expert, 9 MPG is too low for city drivng, I average about 17-18, and that includes city driving. I don't think you have a problem though, It sounds like you are lugging the motor, you are putting unecessay wair on it, causing it to work harder which would result in the low mpg you are getting. I think its good to keep the tranny using all its gears, as there is fluid going through them and it's a good idea to keep all of it used and lubercated. (though if you live in a hilly area it's not bad to use the motor to slow you down) Maybe someone else knows more. Hope this helped, nice choice on cars.
 

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Big_Cadillacs said:
I have a 1992 Sedan Deville with the 4.9L engine and I'm averaging 13.4 MPG. The car is rated at 16 city and 25 highway. It seems to be too low. I always use premium fuel as recommended. Does this seem typical for anyone else? Please share your fuel economy and recommendations to improve it.
:hmm:
i got 198,550 miles on my 1991 fleetwood and get 13cty depending on conditions,but i get 25-26hwy.just put new timing kit in at 197,000,and started using full synthetic oil to try to improve the mileage
 

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94 Fleetwood Brougham
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My 91 got me 29ish highway (not windy day) for 350+ miles. (on FDC, 27-28 calculated)

Typical was 22-24 on FDC, on a good day 25-26. Calc was 1-2 mpg lower.

The only time I ever saw 19 was heavy city driving and/or extreme cold (sub zero F). Most driving was 50-60 miles each way, 55-65 mph for 80% of it, and 30-50 for 20% of it.

The only time I ever saw mine get 12-13 was when I had one cylinder down for a bad injector.

My 91 was very affected wind and jackrabbit starts. It killed mileage fast if you drove it hard. I drove fairly gentle and nailed it only when needed. My LT1 FWB is much more fun!
 

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a sedan deville is a big ass car with a v8 in it. what kind of gas mileage are you expecting? 12-14 mpg for city driving should be considered normal. if you're getting much higher than that, i'm not sure that you could really consider it city driving. if you read everyones posts, those getting over that all include freeway/highway driving. in my 7 mile drive to work i can count on coming to a complete stop at least 10 times, probably more. i'd say it breaks down to about half stop signs and half stop lights of varying durations. all of this being done on roads with speed limits of 30. i pull between 12-14(if i'm lucky) mpg and that is without letting the car warm up by idling.

good luck on actually achieving those epa estimates. if you know of some fairy tale land where those are regularly achieved for an almost 14 year car please let me know because i'd certainly like to move there. listen to the guys who say your average mpg is about right. if you're terribly concerend about mpg you've got the wrong car. the power of a v8 combined with the large frame of a sedan deville equals piss poor gas mileage any way you cut this cookie.
 

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1992 Town Car Cartier & 2014 Accord LX MTX
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Yeah, brand new Consumer Guide got like 12mpg for a 93 Sedan deVille.
When I would get 17mpg in mixed driving roughly 60 highway/40 city, I was happy. If I could somehow get 20mpg for a week, I would be ecstatic!
 

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If you are getting that bad of mileage with a 4.9L V8 car that weighs in at 3600#'s, there is something wrong.

Consider a 4900# 1976 Olds Delta 88 Royale or 98. 455 V8, Q-Jet, no overdrive, THM400, 2.73 gears, EPA rated at 12 city, 18 highway. The 350 in the Delta (which I had) was EPA rated at 13 city and 17 highway. Real world mileage with a teenager (me) driving was 12-13 city and 19 highway, with a small handful fo 23 highway number that we could never explain. (I did it once at an average of 90-100 mph....just made no sense!)

My 1980 Turbo T/A, 3.08 gears, 4030 lbs, carb, turbo, no OD, lousy aerodynamics, got an average of 14 mpg in Dominos driving! And 22-23 highway if you kept it to 62 mph.

Then I swapped in the 455 (1970 455 Pontiac, stock 067 cam, QJet, same trans/axle) in the T/A and got a solid 11 city and 16 highway. I pulled the engine and went through it, put in a Cam Dynamics 284H ([email protected], .480 lift on a 112 with a 112 LC), did some minor head work, and got 11 city and 15 highway. Again, all my highway cruising was 75 mph around 3000 rpm. Screaming for a 455 with no real work going on....

Start fixing it, there is something wrong. It should never be getting that bad of mileage. I would be surprised even with hard starts all the time you get below 16 mpg. My 4400# Fleetwood with the LT1 and me accelerating how an LT1 should with 3.42 gears gets 16-17 city. A 4.9L getting worse than me? Something is wrong.

The 4.9L powered Cads are excellent fuel economy cars. Compare what I got (40K miles worth of recorded data, and I got 19 only a couple times, and that was -10F out) averaging 22-24 city, 26-29 highway ALL the time. Tell me why I would want a pathetic Toyota Camry that gets 31 highway when I can have my Cad V8 get 29 highway?

MPG per CID on the V8 cars blows away the MPG per CID on the 4 cyls.

My 91 Bonneville 3800 V6 got 24-25 mpg in the same type driving as the Cad 4.9, same route, same driving style. It recorded a best of 36.5 mpg (I made it from Colorado Springs, north side, to 30 miles outside of Witchita Falls, TX on 16 gallons of gas averaging 75 mph, and that included 1 overnight stay). Before the cam sensor failed, it was getting 30-32 highway regularly. Once that sensor failed it dropped to 27-28 highway.

Get some good AC Delco plugs, check timing, set to spec, maybe a little higher (I ran 87 octane fuel with timing set around 8 degrees, GM specs 6 degrees for 87 octane, 10 for 91 octane), ensure cap/rotor is good, wires are good, injectors (key!!) are good. Little things add up on a 4.9L V8.
 

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An update:

I drove to Portland yesterday and watched the FDC on the 35 miles I drive on I-5 between Salem and Portland. With the cruise set at 70, the instant mileage indicated between 21-25 most of the time (I-5 is pretty flat on this stretch) and the average ended up at 21 MPG. Like others have said, not bad at all for a full-size car with a V-8.

My 64 Impala gets 13-15 in a mix of driving. It has a 327 V-8 with a four-barrell carb, two-speed Powerglide automatic and a 3:06 rear end, so that's not bad. My Impala and DeVille weigh about the same, so I would say the automatic overdrive and more efficient fuel injection make the difference (At 70 MPH, the Impala is turning about 3400 RPM; no clue on the RPMs on the DeVille).
 

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At 70mph, in my 4.9 deville, I'm turning around 1900rpm.
 

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3400 @ 70 mph? That is more like 3.73's or REALLY short tires. Not 3.06 ratio.

My 455 got better mileage with a heavier car. Tuning/setup. With a 327 I would expect high teens in fuel economy.
 

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Hey rzCaddy, taking your advice I drove around this weekend (in the city) using O/D and I was averaging 18 MPG. I really did not realize how much O/D improves your gas mileage in the city.
 
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