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  1. #1
    FEP Member 83glxdroptop's Avatar
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    Default Fuel economy, mileage of your non V8 ride?

    I have been driving my newly resurrected 3.8L, 3 speed auto convertible to and from work for 3 weeks now and have calculated an MPG of exactly 15 MPG after going through 3 tanks of fuel. I do not drive it particularly hard and I keep the top and windows up. It runs at a steady 2,300 RPM at 65Mph. I drive a combination of city and highway of about 40% and 60% respectively. Can anyone else post their MPG? I am also interested in hearing from those with stock I6 and 4 cyl motors. As far as mods, I haven't made any. Once this week ends I plan to pull some plugs and check their condition. Any suggestions on how to increase this MPG figure? Thanks!

  2. #2
    FEP Power Member In2Fords's Avatar
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    On my bone stock 79 2.3/auto capri I was getting 18/19 freeway or city. The 3 speed really killed me on the freeway, I was turning 4500 rpm at 75mph!!

    My 84 t-top still has the stock german et 4 speed trans and stock geared 7.5, I think 3.45 gearing? I swapped in a stock 85 thunderbird 2.3T, small vam, brown tops, .63 snail, Im getting 24 city and got a best of 29 highway but only being a 4 speed I was turning about 3800 rpm at 70 so that was holding me back I believe. I have the t-bird t-5 and hope that will help once i get a clutch and drive shaft to swap it in, I hear of people getting 34 freeway in 2.3T cars.
    1979 tangerine capri, 40k miles, sn95 8.8, spindles, eibach v8 springs, caster camber plates, manual steering and brakes, Lincoln master cylinder, rebuilt 2.3t/t5 from 85 tbird, nothing much!

  3. #3
    FEP Super Member xctasy's Avatar
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    I am convinced what you have for the 3.8 is what a C5 version does. It's at least got better performance than the earlier 4.2 and much better economy and performance than the 3.3. The 2 and 4-BBL 5.0 SROD and especially the 5.0/T5 is a very well matched engine. The 2.3 is much better at a constant 55 mph, but worse in a common 2.3/3.8/5.0 convoy, where the 4 cylinder needs to be rowed along. Modern highway driving the world over forces poor economy choices.

    The main Mustang problems are the bluff 0.43 drag factor for 83's, and the lack of the right ratio diff with the much better optional AOD. The drag factor on a vert with the roof down is about 0.55 or so, a major drop of perhaps 2 to 3 mpg at 55 mph verses 0.43 with the roof up.


    The standard EPA set-up won't lean cruise on part throttle, won't go rich wide open, and won't stay at 14.7 any more with modern fuel blends, nor will it self adjust or block learn, and its unable to flag non functioning cats or O2 sensors or diagnose faults.

    Frequently, the old Fox engines are gummed up, and need a heads and manifold removal and full valve clean and valve re-seating, and new head gaskets, seals and valve springs and lifters, which suffer in Fords. Then the ignition has to be in spec to suit. Replacement parts are not always reliable. The carb should have its power valve and fuel control valve in good condition, and clean, with a good throttle shaft, and the lead plugs not tampered with. EGR and AIR should be intake and operating, no jammed tees, TVS or control valves. If its Dura-spark, and not EEC IV, it must not have a sticking mechanical advance or perished lines. The 2-bbl gaskets must be pristine and torqued to spec.

    Even so, the Essex 90 degree V6 mpg stats were not much better than the 3.3 and worse than the 2.3. Again, the trade off is performance, where the 3.8 was a nice drive if in tune.

    The 3.45 ratio is the ideal axle, which may not have been an EPA certified option, not 3.08, and the aod is the gearbox, not the C4 or C5.


    All T5 combinations improve economy 10 to 15% on the highway, the 2.3 benefits the most.


    I currently log my consumption on ecomodder. Its figure is 15.44 mpg US as of 03/12/2013.

    http://ecomodder.com/forum/showthrea...der-25017.html.

    I have an I6 81 3.3 Mustang Hatch, a 92 hp low efficiency car with a Revised EPA US Highway/City rating in California spec C3 auto form of
    City:18 MPG (U.S.)
    Highway:26 MPG (U.S.)
    Combine:22 MPG (U.S.).

    The average cold running city figure of 10.3 US mpg in San Francisco like hills of Dunedin, open road warm running best of 17mpg at 62 mph average open road speed, but normally 53 to 73 mph due to traffic flows and grades of up to +/-12%. My overall average is therefore 13.7 mpg vs. the 22 US mpg ideal for the LA basin test.

    Down here, New Zealand is a totally different kettle of fish, with coarse high friction chip seal with a soft structural number (flexible with high deflections under load), very sharp relief with overall average climbs of +4% common to audits, then -4% downgrades on return. It's rare to get dead flat conditions. Automatic transmissions, and road conditions and traffic densities on two lane undivided center line roads make it very, very hard to practice moderation in driving.

  4. #4
    FEP Super Member PaceFever79's Avatar
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    Not a 4 eye but my (heavy) 90 Cougar 3.8 gets around 18 city 22 highway.

    I love the SEFI 3.8, it is a great engine, cruises effortlessly 70-75 mph @ 2000 rpm.
    That is the beauty of the engine, it makes full torque by 2000 rpm!

    If I had an older 3.8, I would consider swapping to the 87+ SEFI 3.8 engine!

  5. #5
    FEP Super Member PaceFever79's Avatar
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    By the way, I think one problem people have with the 3.8 is they don't realize it makes
    torque right off idle and is all in by 2000 rpm! So winding out the gears is just making
    noise and wasting gas. Keep the motor in the sub 3000 RPM power band. Adjust your
    driving style to use that low end torque, and get better mileage.

  6. #6
    FEP Member 83glxdroptop's Avatar
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    Thanks to all. I do not think I have ever even taken it past 3,200 rpm even with my foot though the floor board (separate issue?) so it lives under 2,500 rpm 95% of the time which is why I was wondering about fuel economy. ALL components are new or rebuilt, correctly, from the oil pan up. It was a tired mess when I got my hands on it. So this is what 30 year old technology will make out of a gallon of fuel?

  7. #7
    FEP Super Member PaceFever79's Avatar
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    Not having overdrive is hurting your mileage.

    Because of the low end torque the 3.8 responds well to OD.

  8. #8
    FEP Super Member IDMooseMan's Avatar
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    My stock 2.3L/ET 4-spd (non-OD) averaged, when she was driveable, 24 MPG combined city/highway. My driving was closer to 50% city/50% highway with a 50-mile round trip Monday - Friday. I have the 7.5" 2.73:1 non-locking rear.

    This was obtained performing the usual maintenance (plugs, plug wires, rotor, cap, air filter, oil change, timing, etc) after purchasing the car. The timing was WAY off when I bought her. Best of 17 MPG after purchase. This was worse than my 1997 Ford F350 XLT 4x4 Crew Cab with the 7.3L Powerstroke diesel engine and E4OD auto trans.
    Craig "IDMooseMan" Peters
    1979 Mustang Ghia Notchback, 2.3L, Holley 5200, 4-spd, 3.08:1 7.5" diff, A/C, PS, PB, AM/FM/8-Track, Sunroof, Rear Defroster
    USAF SSgt 63170 1983 - 1992; Co-Founder, Vice President, Omega Delta Sigma, ID-A 2/2015
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  9. #9
    FEP Member 83glxdroptop's Avatar
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    Just to make sure I am doing things "right". I have averaged out three tanks of fuel, pumped from the same pump at the same station, till it just starts to overflow. The new math works out to 16.46 MPG. The motor is a new rebuild with about 800 miles on it. I have noticed that it seems more "settled" as of late. Runs smoother, idles like a champ, no funny smoke out of the pipe. Going to pay attention to driving habits and all of the usual fuel economy topics (properly inflated tires, alignment, proper engine and carb tune, etc.) see if I can squeeze another few miles out of each gallon.

  10. #10
    FEP Super Member IDMooseMan's Avatar
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    Yeah, I think you can do a bit better than that. Don't forget to adjust ignition initial timing, too. Factory specs are a "starting" point. Your actual combination will like more or less (probably more) initial timing. Let us know how she does.
    Last edited by IDMooseMan; 03-13-2013 at 05:30 PM.
    Craig "IDMooseMan" Peters
    1979 Mustang Ghia Notchback, 2.3L, Holley 5200, 4-spd, 3.08:1 7.5" diff, A/C, PS, PB, AM/FM/8-Track, Sunroof, Rear Defroster
    USAF SSgt 63170 1983 - 1992; Co-Founder, Vice President, Omega Delta Sigma, ID-A 2/2015
    To those that serve and have served, "Thank You", to those that haven't, "You're Welcome"
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  11. #11
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    Quote Originally Posted by 83glxdroptop View Post
    Any suggestions on how to increase this MPG figure? Thanks!
    Yeah I have one! Try some fuel from another state. (other than CA/AZ in winter)

    WE in MI have been finding that the oxygenated fuels are of lower and lower octane ratings lately! So much so that there is a inverse affect in MPG as a result of SUB 87 octane fuels.

    Here there is no state standards for fuel - only measures. When stations get bunk fuel -read E85, subgrade 87 and under or left over oxygenated from neighboring states MPG suffer. Cars will run on it - as most computers will dial back the timing to compensate for the knock. BUT MPG suffers as we still have to move car from rest to movement, and MANY are not light anymore.
    (cars and drivers)

    Mark

  12. #12
    FEP Super Member webestang's Avatar
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    Quote Originally Posted by In2Fords View Post
    On my bone stock 79 2.3/auto capri I was getting 18/19 freeway or city. The 3 speed really killed me on the freeway, I was turning 4500 rpm at 75mph!!
    That's my 85...................I NEED A 5-SPEED!!!!

    Scotty
    1985 Fox Notch 4-banger Ranger tube header Eastwood Royal Blue
    1988 Fox LX 5.0 AOD Vert BBK 170mph speedo Candy Apple Red
    1999 Mustang Coupe V6 Auto Chrome Yellow -Daily Driver.
    Past Pony's.....
    68 Coupe Inline-6 3-Speed-Man. Primer
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  13. #13
    FEP Super Member PaceFever79's Avatar
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    Yep, OD makes all the difference!

    My 90 cougar SEFI 3.8 AOD is turning 2000 rpm at 70 mph. And she has no trouble
    maintaining that speed on cruise averaging 22-23 mpg highway.

    The original poster has a carb with no OD, both are costing mileage. Make sure the idle
    mixture is set as lean as possible yet still drives well. That right there will burn up a lot
    of gas idling in stop and go driving if the idle is set too rich.

    If it were mine, I'd look into both an EFI and AOD swap (if mileage was a concern).
    If all that you're trying to do is improve mileage, as other people have suggested,
    make sure that your engine and carb are in tip top tune.

  14. #14
    FEP Member LSCR351's Avatar
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    My 86 Coupe has a carborated 2.3, C3 automatic, 3.27 gears, 16" Pony wheels. Gets 25 on the highway.

    Wifes 93 GT with Dual-Plug EFI 2.3, T5 standard, 3.45 gears, 16" Pony wheels. Got 27 on the highway. I say got, because I have not refigured it since adding the snail.
    69 Mustang Fastback= EXPENSIVE
    84 SVO= project pick up the front wheels
    86 Coupe= project show car
    87 Mark-VII Vortech'd351/T56= TROUBLE
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    99 P71 the "PO-RAUDER"=weekend ride (awaiting built motor)
    00 Excursion 7.3PSD= long distance trips
    05 F250 V10 SCSB= the Hot-Rod pick-up, trailer puller
    Wifes rides: 97 Exploraineer Sport V8= DD, 93 GT 2.3t/T5= backup, 05 F250 SCSB 4X4= toy

  15. #15

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    Well, I have and 86 3.8L vert. It has the central (throttle body type) fuel injection. According to my mechanic I have a C4 trans (not the factory C5, he should know, he was changing the filter). Factory 2.73 rear, as far as I know. I know that my mileage figures are off because the speedometer reads slower than you are going be a large percentage (it shows 45mph when a gps shows 55) due to wrong size tires and probably wrong speedo gear in the trans. I've put a bunch of work into getting it in tune (not rebuilt. doesn't have super oil pressure) and I still have a code for air bypass not working that I haven't had time to fix. Anyway, by just gallons of gas and trip meter count I get about 16mpg. So figuring an adjustment for it counting the miles wrong:

    18mpg.

    EPA rates the thing at 17 city 21 highway, so I don't have much hope for better. Rated 16 and 24 on the 5.0. Hmmmm.....
    1986 Mustang LX convertible 3.8L V6 C4 auto
    1975 Ford Gran Torino 351W C4
    1995 Ford F150 XL 5.0L 4R70W
    2015 Mustang 3.7L V6/auto

  16. #16
    FEP Senior Member tcruise's Avatar
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    It's not the age of the car, it's the total package. I had an '87 Buick A-body with 3.8 V-6 MPFI, and auto trans with overdrive. GM set all of these up for maximum mileage, all upshift at a low RPM. Mine got in the 20s consistently. '91 Sable with 3.8 did too. Same for Corvairs (2.7L six-cylinder), made in the '60s!

    The 3-speed auto is killing your mileage. A 5-speed manual would make a big difference, though it will probably take a year to pay off unless you get if for free, LOL.

    What grade of gas are you using? I'd go with the highest. Engine will run better, no detonation. Also, you don't have the bubble back like I do (supposed to help with streamlining). My '83 Mustang (bubbleback) with 5.0 and 4-speed gets 15+ MPG.

    I've noticed that often, the smaller engines actually get worse mileage than bigger engines. For example, '65 Fury with 225 slant-six versus '63 Valiant with 170 slant-six both got 15 MPG, even though the Valiant was a lot smaller (and lighter, I assume) and engine displacement was WAY smaller. Oh, yeah, the Valiant had the 3-speed auto, Fury had 3-speed manual.

    How tall are your tires? Taller tires improve mileage, though your car has lower gearing than mine (runs at 3200 RPM at 60 MPH). Still, the V-8 easily pushes the Mustang at freeway speeds. I'm sure that helps with fuel economy.

    If you want really good mileage, get a Honda Civic!
    1983 Mexican Mustang 5.0/4-spd
    1982 Capri RS 5.0 H.O.

  17. #17
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    I always thought is was a misnomer that small engines mean better gas mileage, it doesn't. My factory 5.l 5 speed with original 2.73 gears gets almost 25 mpg on the highways and around 18-19 mixed city town driving depending on how heavy my foot is. It's all in the gearing and the setup not just on the displacement. You can enjoy the incredible factory power out of the 5.0 and also have a fairly good gas consuming vehicle. That's whyi never understood people buying the smaller motors in these cars just to save on gas. My old 93 corvette had a 350 V8 and It got sometimes over 30 mpg, and all the soccer moms and granola crunching minivan and SUV owners with their supposedly gas stipping v6s were all getting 14-18 mpg. I'm still amazed at how well these old 5.0 5speed foxes are geared and designed from the factory. Even with my factory installed 2.73s I've got plenty of gear and quickness out of the whole, a nice duration prior to second, and on the top end my RPMs are well under 2000 for highway cruising in 5th gear, so a very nice configuration.
    Last edited by vascj; 03-15-2013 at 06:09 AM.

  18. #18
    FEP Power Member In2Fords's Avatar
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    One thing to note, when you fill up don't fill the neck, it just evaporates.
    I always only fill till it clicks and never top off. In my old bii if the pump monkey would top it off I would stall real often and run rough for the first few miles.
    Its even three law in Oregon no topping of fuel.
    1979 tangerine capri, 40k miles, sn95 8.8, spindles, eibach v8 springs, caster camber plates, manual steering and brakes, Lincoln master cylinder, rebuilt 2.3t/t5 from 85 tbird, nothing much!

  19. #19
    FEP Super Member PaceFever79's Avatar
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    Quote Originally Posted by vascj View Post
    I always thought is was a misnomer that small engines mean better gas mileage, it doesn't. My factory 5.l 5 speed with original 2.73 gears gets almost 25 mpg on the highways and around 18-19 mixed city town driving depending on how heavy my foot is. It's all in the gearing and the setup not just on the displacement. You can enjoy the incredible factory power out of the 5.0 and also have a fairly good gas consuming vehicle. That's whyi never understood people buying the smaller motors in these cars just to save on gas. My old 93 corvette had a 350 V8 and It got sometimes over 30 mpg, and all the soccer moms and granola crunching minivan and SUV owners with their supposedly gas stipping v6s were all getting 14-18 mpg. I'm still amazed at how well these old 5.0 5speed foxes are geared and designed from the factory. Even with my factory installed 2.73s I've got plenty of gear and quickness out of the whole, a nice duration prior to second, and on the top end my RPMs are well under 2000 for highway cruising in 5th gear, so a very nice configuration.
    As you say, there are many factors for mileage

    Power to weight ratio
    Engine tune / efficiency (HP per liter)
    Gear ratio, tires, and aerodynamics
    Climate (warmer climate uses less fuel)
    Driving style (getting optimum mileage takes skill)
    Terrain (flat terrain gets a lot better mileage than hilly terrain)

  20. #20
    FEP Member 83glxdroptop's Avatar
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    Looks like I am where I am supposed to be as far as mileage is concerned. I wanted to get input from others so that I may see what is typical. Interesting numbers with the different engine/trans combos. I will be using my car for weekend cruising to the beach and other interesting parts of town. Mileage is not really a concern aside from having the car run correctly. The purpose of this car for me is to have fun. My daily driver is an LS400 and I drive that because it is quiet and comfortable. Fuel economy is not really at the top of my "must have" car qualities.

  21. #21
    FEP Power Member jessew's Avatar
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    Quote Originally Posted by In2Fords View Post
    One thing to note, when you fill up don't fill the neck, it just evaporates.
    I always only fill till it clicks and never top off. In my old bii if the pump monkey would top it off I would stall real often and run rough for the first few miles.
    Its even three law in Oregon no topping of fuel.
    If I try to top off, my car floods.
    1983 Mercury Zephyr Z7 AM Radio, no a/c, 200 3.3l I6, C5 Automatic, Police scanner, 40 Channel Cobra 29LTD CB radio, PA system mounted under bumper

    2008 Ford F150 XL 2wd v6, 5 speed.

  22. #22
    FEP Super Member IDMooseMan's Avatar
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    I fill my gas-powered vehicles like I fill my diesel truck; lock the nozzle on the lowest setting. When it clicks off, the tank is full. Grab the receipt and go play.
    Craig "IDMooseMan" Peters
    1979 Mustang Ghia Notchback, 2.3L, Holley 5200, 4-spd, 3.08:1 7.5" diff, A/C, PS, PB, AM/FM/8-Track, Sunroof, Rear Defroster
    USAF SSgt 63170 1983 - 1992; Co-Founder, Vice President, Omega Delta Sigma, ID-A 2/2015
    To those that serve and have served, "Thank You", to those that haven't, "You're Welcome"
    2.3L Horsepower Potential Thread
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  23. #23
    FEP Power Member jessew's Avatar
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    Quote Originally Posted by IDMooseMan View Post
    I fill my gas-powered vehicles like I fill my diesel truck; lock the nozzle on the lowest setting. When it clicks off, the tank is full. Grab the receipt and go play.
    I have to guess, F 350?
    1983 Mercury Zephyr Z7 AM Radio, no a/c, 200 3.3l I6, C5 Automatic, Police scanner, 40 Channel Cobra 29LTD CB radio, PA system mounted under bumper

    2008 Ford F150 XL 2wd v6, 5 speed.

  24. #24
    FEP Member LSCR351's Avatar
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    I'd bet Ford sells, and has sold, more Diesel trucks than GM and Dodge combined!
    69 Mustang Fastback= EXPENSIVE
    84 SVO= project pick up the front wheels
    86 Coupe= project show car
    87 Mark-VII Vortech'd351/T56= TROUBLE
    93 Town&Country= DD/work van
    96 F150 Lightning FlareSide= boat hauler
    99 P71 the "PO-RAUDER"=weekend ride (awaiting built motor)
    00 Excursion 7.3PSD= long distance trips
    05 F250 V10 SCSB= the Hot-Rod pick-up, trailer puller
    Wifes rides: 97 Exploraineer Sport V8= DD, 93 GT 2.3t/T5= backup, 05 F250 SCSB 4X4= toy

  25. #25
    FEP Super Member mustangxtreme's Avatar
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    When my 83L had the 3.8, c5, and a 2.73 gear, I was getting 20mpg average. If you are running a c4 you won't have a lock up torque convertor which will cost you some.
    Dave

    If common sense was common wouldn't it just be sense?

    1983 Capri L T top 5.0 efi aod
    1983 Capri RS Turbo
    1981 Black Magic 400 c6
    93 F-250 351 5sp 4x4

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