International Full Size Jeep Association
Home Forums Reader's Rigs Tech Library Trail Stories FSJ-List
International Full Size Jeep Association  

Go Back   International Full Size Jeep Association > Tire Kickin' > General FSJ Discussion

Thread Tools Search this Thread Display Modes
Old 04-25-2006, 04:17 PM
skunked skunked is offline
Join Date: Feb 07, 2004
Location: Portsmouth, VA
Posts: 190
Gas mileage improvements..

Yes this kind a thread has been around before..but who has good ideas or mods to boast our mileage?
Scout Jeep Jeep
Reply With Quote
Old 04-25-2006, 05:17 PM
drlocke's Avatar
drlocke drlocke is offline
Roadside Mechanic
Join Date: Dec 29, 2003
Location: Western MA
Posts: 9,725
Drop your keys down the well.
Reply With Quote
Old 04-25-2006, 05:25 PM
88GWSteve's Avatar
88GWSteve 88GWSteve is offline
Gear Head
Join Date: Aug 26, 2005
Location: Lewes, Delaware 19958
Posts: 563
Get one of these....
Or if you wanna do keep it, just do basic maintenence, keep it tuned, TFI install, rebuild carb if needed, etc.
1988 Grand Wagoneer, mostly stock, Holley 2bbl carb, and new Sony stereo

"My lug nuts take more torque than your Honda makes"

Reply With Quote
Old 04-25-2006, 05:33 PM
Spectre's Avatar
Spectre Spectre is offline
FSJ Maniac
Join Date: Nov 26, 2004
Location: Dallas, Texas
Posts: 4,219
Originally Posted by skunked
Yes this kind a thread has been around before..but who has good ideas or mods to boast our mileage?

In terms of effective modifications to increase mileage (regardless of price):

1. Overdrive transmission.
2. Multipoint Electronic Fuel Injection.
3. Convert to a diesel engine, which, surprise, can come with an overdrive transmission.

Other than that and keeping your boot out of it, there's not much you can do.
"Battlewagon": 1986 Jeep Grand Wagoneer (w/ Tow Pack) - Urban Assault Wagon under construction - TFI, TBI, CS144, Aftermarket Sanden, Explorer Power Seats, 4" Lift, 16" AHI wheels and much much more; click here for a full list of modifications and gear, links to writeups/posts and more info.

Daily Driver: Modified 1987 Jaguar XJ6 Vanden Plas.

Last edited by Spectre : 04-25-2006 at 05:40 PM.
Reply With Quote
Old 04-25-2006, 05:33 PM
Don S's Avatar
Don S Don S is offline
Gone,But not Forgotten.
Join Date: Feb 06, 2002
Location: Burleson TX
Posts: 5,613

Boosting Fuel Mileage
... It takes X amount of power to move gasoline engine vehicles from point to point. The engine converts gasoline to heat as the power source. Much more than fifty percent of the heat is wasted unused and is dissipated though the radiator and exhaust system. Large cubic displacement engines normally consume more fuel than smaller engines but this is not a ‘hard’ fact.
FOOD for THOUGHT. Why are four cylinder engines capable of better fuel mileage than six or eight cylinder engines of the same size and at the same RPM? This is due to the longer duration of the combustion stoke allowed by fewer cylinders. The longer duration for the burning process in a four cylinder is double that of an eight cylinder. The eight is more wasteful in theory than the four or six cylinder engines. More cylinders shorten the time that combustion has to finish the job of totally burning all the fuel especially at max power out put. One of the fuel saving technologies of the day is reducing the of fuel using ‘cubic inches’ of the engine when full power is not required.
... Here is a list of a few of the mechanical things that can effect fuel mileage.
Cam and ignition timing, cam lift, duration and valve size. Leaky fuel delivery systems with vented vapor losses, restricted air induction systems i.e. dirty filters. Intake air can also be too hot or cold. Restricted exhaust scavenging systems. Operating temperatures of fuel and engine. Carburetors with bad power valves, accelerator pumps and fouled choke systems. Carbon fouled injectors, sparkplugs, and piston rings. Type of transmission, automatics without lock-up converters and over-drives, gear ratios. The type of tires, tire size, the tire pressures and the wheel alignment. Example; Just think, is it possible that larger wider tires require less ‘toe in’ that could reduce drag and get better fuel mileage? But the larger wider tires cause increased air flow resistance.The vehicle speed, the load, the wind speed and direction. The list can continue on including the type and additive mix of the gasoline. Gasoline blends are changed continually by local area, altitude and season. These are changes in the volatility of the gasoline. Winter Gasoline will evaporate much faster in the summer temperatures and less octane is required at high altitudes.
The driver knowledge and ability is the big factor for achieving the best fuel mileage if the vehicle is in proper condition.
Make sure the odometer in the vehicle is showing correct mileage. Increasing the diameter of the tires will reduce the amount of miles shown on the odometer. Keep a record of all fuel amounts, the mileage and the Miles Per Gallon between each gas-up. The record can be helpful in spotting problems with the engine when there is a sudden drop in mileage.
An example of the simple formula is 200 miles divided by 10 gallons = 20 MPG
Full tank amounts will vary due to air trapped in the tank but the MPG will average out in the long run.
Here are a few thoughts about saving fuel.
First thing a driver will notice when they start to conserve fuel is it will agitate other drivers around his vehicle. Please be considerate of other drivers who have no concept of your economy driving. The other drivers want to race to the next stoplight and remember, if they don’t get there quick enough they won’t get to stop!
1. Think about driving as an art while doing so. Stop rubber-necking, turn off the music, turn off the cell and drive.
2. Install a dash-mounted vacuum gauge and use it. As the fuel mileage drops the vacuum needle drops. Try to prevent the needle from dropping below five inches. Readings will change with altitude changes.
3. Drive as if you had a fresh egg taped on the accelerator AND brake pedals.
4. Apply accelerator and brake petals smoothly.
5. Reduce speed as much and as soon as possible. Speeds above 50 MPH eat into the pocketbook!
6. Scan far ahead of your vehicle for traffic control signals and things that will allow you to ‘get off the gas’ sooner so you don’t have to ‘hit’ the brakes as hard – later. The over use of brakes means fuel has been wasted.
7. Drive as if your afraid your brakes are in poor condition and you are trying to save them.
8. Purchase your fuel in the morning when it’s cool and keep the tank full.
9. Air you tires up when they are cold and on the plus side of the recommended pressure and check them often especially on cold days.
10. Small amounts of high quality low ash synthetic Out Board 2cycle oil in the fuel (less than ¼ Oz per gallon) will clean and lubricate and reduce friction. The low ash oil will help the following items for better fuel mileage and life; electric gyrator fuel pumps, carburetor/injector parts, spark plugs, valve stems, compression rings and EGR systems. One sticky fuel injector can drop fuel mileage by up to one third.
11. Air dams can enhance cooling and reduce aerodynamic drag. Reduce the amount of air getting under the truck because the underside of vehicles create much air turbulence and drag at highway speeds. Bug shields, sun visors, wind deflectors, roof top racks and large outside mirrors can reduce fuel mileage.
12. The effect of heavy loads is detrimental to fuel mileage and brake life.
13. Modifying a vehicle with lifts and large wide tires is detrimental to fuel mileage and brake life.
14. Cruise control may save fuel in ‘flatlands’ but may not be economical in hilly country.
15. In hilly country do not allow the down hill run to cause engine ‘braking’ i.e. slowing down the vehicle unnecessarily. Run your fastest speed at the bottom of a hill and the slowest at the top. ... Only use engine braking when the vehicle is going to gain excessive and unsafe speed that would have required a fair amount of regular brakes. Excessive downhill braking can cause many heat related problems. Among these are warped rotors, brake fade, boiling brake fluid, wearing out pads, over heating seals, bearings and lubricants.
... Down hill engine braking and downshifting for increased engine braking is not going to consume very much fuel because the throttle will be closed. Long downhill runs of five or more percent grades are a good time for downshift engine braking. Two miles of seven-percent grades with curves should be mandatory.
So in hilly country it's a case of the having to use more throttle to regain the speed you lost by allowing short periods of unnecessary engine braking.
16. Allow the engine to warm up and/or drive gently till it does. Cold engines get poor fuel mileage.
17. Put the transmission in neutral or stop the engine when long waits in traffic are encountered i.e. train crossings and long red traffic lights.
18. Reduce the Air Conditioning and the electrical demands on the alternator. Alternators draw much horsepower and extra fuel so fancy lights and sound systems burn extra gasoline and bother other peoples eyes and ears.
19. If the automatic transmission is equipped with overdrive and/or lock-up torque converter learn at what speeds it changes gears/locks. Often one can get the transmission into overdrive and lock the converter sooner by backing off the accelerator pedal a little at the right time.
20. The use of WOT (Wide Open Throttle) to gain speed is wasting fuel.
21. Some people are claiming fuel mileage gains by adding small amounts of acetone to their fuel. There is an Acetone article in the Fuel Tech Section.
22. Hey!.. wake-up!! We are sorry we put you to sleep… do you have any other ideas?

Have a good one and CUL.. Don S..
Sold our 1976 Wagoneer 406, MC4300, TH400, QT, TruTrac, 2" lift, 31x10.50s, duel Optimas,
It’s took us over 161 Colorado Mountain Passes, 3 Jeep Jamboree USAs & 2 Ouray Invasions from 1985 to 2010
Reply With Quote
Old 04-25-2006, 05:38 PM
66rustbucket's Avatar
66rustbucket 66rustbucket is offline
Join Date: Apr 24, 2006
Location: Montpelier, ID
Posts: 99
I've started running amsoil in my motor and that helped a bit. They say if you replace all fluids from front to back you can expect a 5 to 10% increase in gas mileage. Just a thought...I'm getting 14 mpg in my 66 Gladiator with a buick 350!
Reply With Quote
Old 04-25-2006, 06:05 PM
drlocke's Avatar
drlocke drlocke is offline
Roadside Mechanic
Join Date: Dec 29, 2003
Location: Western MA
Posts: 9,725
Seriously on this topic:
1) Do a complete engine analysis and assess compression from cylinder to cylinder and then do a followup leakdown test every cylinder. If compression readings are extremely variable from cylinder to cylinder then analyse leakdown findings to determine if air injected into the cylinders via sparkplug hole is leaking past exhaust or intake valve, or head gasket or rings. You may find yourself doing a complete engine overhaul, or you may find that you only need to pull the heads and clean out carbon deposits.

Assess condition of the valve train, including sprocket and chain assembly for slop, and cam for lobe conformation.

Overall the engine needs to be operating within proper tolerances for all working surfaces.

2) After the engine mechanical has been covered then do a complete tuneup, including checking the distributor advance curve and make sure the distributor components--such as flyweight springs and the like--are still up to snuff, and that the drive gear for the distributor isn't unduly worn. Make sure points or pickups are in good shape, and make sure that all plugs are gapped properly.

3) Overhaul carburetor to ensure that it is operating in all aspects--including such as jetting, idle fuel metering and automatic choke, etc--to its utmost efficiency by design--which isn't saying much as far as fuel economy is concerned in most cases. Better to try TBI or MPFI if you can manage.

4) Check transmission and driveline to make sure they are at 100%.

5) Check chassis geometry and wheel alignment for optimum adherence to spec.

6) Check brakes to make sure they are stopping the vehicle when you want to stop, and not trying to when you don't.

7) Check tire condition and pressure often.

Understand overall that if you have made a vehicle with gear ratios and limited slip differential for off-road use then it will not be a good vehicle for the DD on the highway to work and back if fuel costs are a concern.

Also understand that if you have an FSJ my advice in my previous post is by and large the best measure in saving fuel. My own waggy is uncompromisingly boxy and non-aerodynamic, and to borrow and butcher a phrase from E.B. White in "Farewell My Lovely", a reminiscence about the model T Ford: ....uncompromisingly erect ...and the [8] cylinders push the [vehicle] through the atmosphere with a total disregard of physics...."
Reply With Quote
Old 04-25-2006, 06:08 PM
drlocke's Avatar
drlocke drlocke is offline
Roadside Mechanic
Join Date: Dec 29, 2003
Location: Western MA
Posts: 9,725
As predicted by me as I was interrupted in writing my spiel, Don S to the rescue, with a much more comprehensive and better treatise than I could ever wish to give.

Way to go, Don S.! LOL

What he said.....
Reply With Quote
Old 04-25-2006, 06:54 PM
FSJeeper FSJeeper is offline
King of Unfinished Projects
Join Date: May 20, 2000
Location: Texas
Posts: 5,268
Don S did a great job for what to do with a gas engine in a FSJ. No matter what you do though, mileage with a gas motor is not going to ever be outstanding with a gas engine. Aerodynamics of a FSJ are non-existent.

A diesel will improve your mileage dramatically. Non turbo mid 80's Blazers with the 6.2 were EPA rated at 29 mpg on the gallon. It is an easy swap.
In Process: 91 Wagoneer, D61/71 axles with 3.07 gearing, NV4500, NP205. Cummins 6BT.

Back burner project: Crew cab M715, Cummins/Allison/Rockwell Tcase/Dana 61/Dana 71.
Reply With Quote
Old 04-25-2006, 07:13 PM
drlocke's Avatar
drlocke drlocke is offline
Roadside Mechanic
Join Date: Dec 29, 2003
Location: Western MA
Posts: 9,725
The E.B. White quote I excerpted from an article describing the model T Ford--that I miserably butchered before--actually reads.....

"Directly in front of the driver was the windshield - high, uncompromisingly erect. Nobody talked about air resistance, and the four cylinders pushed the car through the atmosphere with a simple disregard of physical law."

Sound somewhat familiar?

I will post this as a separate article soon. Look for it, as it is to my way of thinking worthwhile reading and such as most of us would enjoy.

Last edited by drlocke : 04-25-2006 at 07:15 PM.
Reply With Quote
Old 04-25-2006, 07:34 PM
funwheeling's Avatar
funwheeling funwheeling is offline
Master Mechanic
Join Date: Nov 21, 2004
Location: Central SC
Posts: 1,262
These vehicles are not made for fuel economy. Look now at the commander 14/19.
The best way for you to get good milage out of your wag is to put stabilizer in your tank and drive a hybrid.
I doubt that anyone will be able to get any more then a lucky 15 mpg out of these ever without a lot of cutting chipping and ducktape.

Just my opinion.

I didn't buy mine to save dinosaurs.

Like trying to squeeze water out of rocks in the desert.
1991 Grand Wag "The Phoenix!" IS back from the ashes!!!
My Yahoo
BJ's 6" lift
Holley Truck Avenger 670CFM
Mickey Thompson Wheels
Dick Cepeck FC-II
Killer 32 Nurf Bars
Comp Cam 260H
MSD Distributor, Coil and Controller
Edlebrock Headers
Dual Exhaust 2 Flowmaster 50's
Reply With Quote
Old 04-25-2006, 07:37 PM
rawdave's Avatar
rawdave rawdave is offline
Master Mechanic
Join Date: Jun 13, 2000
Location: Zebulon, Ga. USA
Posts: 1,009

This guy provides low-cost DIY manuals on increasing fuel mileage up to 100%.

I have read the manuals and once my Jeep is completely tuned with the new MPFI, I intend to implement several of his suggestions.
"You fancy people with your shoes."

87 Grand Wagoneer
2009 GMC 5.3L Vortec
Sterling 10.25 Rear
8 Lug J10 Front
TSM Mfg Rear Disk Brake Conversion
33 Gallon Rear Poly Tank

69 J-3000 Pickup

2.8 Cummins Diesel Repower
Atlas Transfer Case
Reply With Quote
Old 04-25-2006, 09:47 PM
steven79's Avatar
steven79 steven79 is offline
Bleedin' Gasoline
Join Date: Jul 25, 2001
Location: Drumright OK.
Posts: 2,257

Just tested mine last trip to keystone lake, 16.6 at 60 mph thats useing a gps to check mine, when i used the old speedo i get 11 mybe but i know it is way off. In town i very between 9 and 12 mpg. It is all in the tuneing and condition of the motor.
Thor - 79 wag ltd <br />366,th400,Q trac d44 f/r 3.54<br />31x10.50x15 Good year at's
I am not a dad,I am a domestic dictator
Reply With Quote
Old 04-25-2006, 10:00 PM
will e's Avatar
will e will e is offline
Always Broke
Join Date: Nov 16, 2001
Location: Mesa AZ
Posts: 9,996
Originally Posted by steven79
Just tested mine last trip to keystone lake, 16.6 at 60 mph thats useing a gps to check mine, when i used the old speedo i get 11 mybe but i know it is way off. In town i very between 9 and 12 mpg. It is all in the tuneing and condition of the motor.

Unfortunatly you can't determine accurate gas milage on one trip or one tank of gas. It is almost impossible to get the tank exactly to the same fill point as the last. Temp can have a impact on this as well. It doesn't take much. A 1 gallon difference in a 10 gallon fillup throws off the results by 10%. That is, if you went 100 miles and you got 10 gallons in it is 10mpg. If you got 9 gallons you will think you got just over 11mpg. (Steven79 this isn't directed at you specifically).
82 Cherokee WT – SFwith Alcan/agr box/Borgeson shaft/ 401/performer/Holley TA/HEI/BeCool/727/ALTAS(2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave,Discs, ARB,Artec Truss)/MTR 37/Corbeau Moab Seats /Hella/tuffy console/sliders/custombumpers&roll bar/WARN 8000/steering brace/CO2 Tank/dual batts/custom TCskid plate

Reply With Quote
Old 04-26-2006, 05:30 AM
drlocke's Avatar
drlocke drlocke is offline
Roadside Mechanic
Join Date: Dec 29, 2003
Location: Western MA
Posts: 9,725
Originally Posted by steven79
Just tested mine last trip to keystone lake, 16.6 at 60 mph thats useing a gps to check mine, when i used the old speedo i get 11 mybe but i know it is way off. In town i very between 9 and 12 mpg. It is all in the tuneing and condition of the motor.

I'm gonna get a gps installed in my Wag first thing tomorrow!
Reply With Quote
Old 04-26-2006, 07:25 AM
Serious Johnson's Avatar
Serious Johnson Serious Johnson is offline
AMC 4 OH! 1
Join Date: May 19, 2002
Location: Pumpkintown, South Carolina
Posts: 3,831
Following up on some points above:

The vacuum guage/egg thing works OK-ish for a big 'Murican boat with a V8 & slushbox, but who drives those anymore ? For a fuel-injected 4-cylinder car with a manual transmission, it's most efficient to get up to speed quickly, using large throttle openings (but not quite full-throttle, which imposes open-loop mode), and shifting at very low revs. Less pumping loss from an open throttle is more efficient. That's a diesel's main advantage. Get the heck out of those lower gears as soon as possible and, above all, waste no revs!

Warm-up can only hurt -- you're getting zero MPG during that time, and causing the motor to come up to temperature much more slowly. Just start it up and drive off immeiately but, as said, gently.

Aerodynamics & other drag are certainly important. I've noticed that, in flat country, I get about the same fuel mileage when towing an empty car hauler as when there's another 5,000 lb aboard. A Wag or narrow Cherokee are not all that horribly shaped, particularly with the small stock mirrors & no roof rack. Some modern SUVs are worse -- I'm thinking of that one named for a blow-job.

In certain cases, for instance, a stock wag with a slushbox tranny & 2.72 gears, slowing down below typical highway speed doesn't help. I've seen such a rig, in perfect condition, get slightly worse economy at 50 MPH than at 75. I blame poor low-rpm efficiency in the non-lockup torque converter.

My Wag, modified with a hotrod 360, fuel injection, manual tranny, 3.73 gears, dual limited-slips, 33" tires, & 4" lift gets about 20 MPG in the mountains if I drive like I have some sense. It could do only a little better than half that when it was stock.

"Carpe Mañana".

'83 Wagoneer
360, .030-over, K8600 cam, Crane springs, ported heads, Edelbrock Performer, G.M. TBI, TFI, 3" exhaust,
T-18a/208, D44/AMC 20 w/ limited slip in both, 3.73s, 33s, BDS 4" springs, Rancho 9000 shocks, etc., etc.
Reply With Quote
Old 04-26-2006, 07:32 AM
janie's Avatar
janie janie is offline
Dexron Impaired
Join Date: Aug 11, 2001
Location: Mallards Roost, TX
Posts: 8,270
Leave the tailgate down. Every lil bit helps.
He is your friend, your partner, your defender, your dog. Faithful and true to the last beat of his heart. You owe it to him to be worthy of such devotion.
Reply With Quote
Old 04-26-2006, 07:35 AM
drlocke's Avatar
drlocke drlocke is offline
Roadside Mechanic
Join Date: Dec 29, 2003
Location: Western MA
Posts: 9,725
Originally Posted by janie
Leave the tailgate down. Every lil bit helps.

I have that tailgate delete option on my I-bird pickup.
Reply With Quote
Old 04-26-2006, 07:59 AM
JeeperJay's Avatar
JeeperJay JeeperJay is offline
Grease Monkey
Join Date: Apr 26, 2005
Location: Bellingham, MA
Posts: 324
Adding an electric fan should help a little bit....right?

That is my next planned modification. Get rid of the giant mechanical fan and install an electric one. Oh yeah, and downsizing back to 31" tires. D'oh!
Jason T.
'04 Grand Cherokee: Silver/ black. 2" lift
'02 Grand Cherokee: Black/black Laredo with a V8 and Selec-Trac- Totaled in Sept.'07
'90 Woody:White/maroon. TFI, BJ's 4" & 33" BFGs. Gone but not forgotten
Reply With Quote
Old 04-26-2006, 08:10 AM
pb's Avatar
pb pb is offline
Master Mechanic
Join Date: Aug 28, 2003
Location: Leslie, MI 49251
Posts: 1,443
Weight = crappy mileage for stop and go driving
Aerodynamics & drivetrain = crappy mileage on highway

The heavier the object, the harder it is to start moving from rest. That's why newer aerodynamic SUV's the same weight as ours get the similiar city mileage. Not going fast enough for aerodynamics to make a great impact on mileage in city driving or for overdrive to kick in.

Aredynamics and drivetrain are important at steady speeds. An object in motion tends to stay in motion until an outside force acts upon it (air resistance & gravity) SJ described this when talking about towing. It takes less energy to keep the mass in motion than it is in getting it to that speed, not getting into the momentum/weight aspects. The more efficient the drivetrain, less energy is expended in overcoming the outside forces and remaining in motion. This is why you can get better mileage with a diesel, efi and/or overdrive in a nonaerodymanic FSJ at highway speeds as compared to stock components.

As far as improving mileage, lighten the weight and increase the drivetrain efficiency as previously mentioned.
1975 Wagoneer DD
360 with large cap ecm controlled HEI, TBI EFI, Comp Cam 260H, Edelbrock Performer Intake, CS130 alt, 4 row radiator, S10 steering box, QT w/LO, WT 3.54 D44 axles. Rancho 9000X's, ~4" lift, Caddy rear discs.
Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -6. The time now is 09:02 AM.

Powered by vBulletin Version 3.5.4
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
corner corner