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Improving fuel mileage TJ (others???)


 
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conrman
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Joined: 27 Oct 2006
Location: Keller, TX

PostPosted: Fri Oct 27, 2006 10:02 am    Post subject: Improving fuel mileage TJ (others???) Reply with quote

New to the TJ, been driving CJs for years.
Mine is a 1998 all stock 4.0l, 3.08, 5spd (ax-) 31 inch BFG All Terr tires 7 inch rim, stock injection 180hp-185hp I think. 82k miles.
Mileage was horrible (14-16mpg sea level-1500ft cheap gas..worse if I use 5th, I don't) compared with a similar setup 1985 cj I owned, 4spd 4.2l, 3.43ish gears, (17-20 mpg at 5500-9000ft.altitude, cheap gas) 31inch BFG All Terr tires 8 inch rim, carb, 110-125hp. 96k miles
This basic setup gets me to about 80%-85% of the places I need to go once aired down a touch and sway-bar disconnected.

I have found 1-2 mpg measurable gain.....

My brake calipers on the TJ were dragging, big time, rears were hanging up also.....I completely dismantled any part that could prevent the piston, pad or calipers (drum, shoe) from retreating from the disc/drum.
There was crud (dirt, brake dust and corrosion) built up on several parts not directly responsible for braking, but allowing the pads and shoes to move freely toward and away from the disc and drum.
I cleaned all of these parts and buffed and (lightly)greased the pins and parts that created the interference, and reassembled, changed the dirty fluid.

There is no measurable increase in braking, but the jeep seems to coast twice as far as before, the tires spin much freely when on jacks even after brakes are applied. I have measured an increase of 1-2 mpg over the past month city and highway. I now get 15.8 (various speeds)-18 mpg (at 70-73 mph highway....hardtop or soft, a/c on or off).

Time will tell if the light grease attracts dirt over (?) period of time... But it was easy.....If grime builds quickly, I will try again without the grease.

I thought the lack of hubs might be the major determining facter in the diff. in milage between the cj and tj. But this was a big suprise.

Looking to increase milage even more, with this basic setup, under everyday driving.....

any other ideas.....reducing parasitic drag, remap the powerplant, gearing (may be worth .5-1 mpg)

Tire change may be cheaper, lots of trade offs though. BFG's All terrains love picking up rocks and holding them until you are on the highway.....where they sling them.

P.S. don't grease anything near your brake systems unless you are absolutely certain of the where and why and what I just mentioned.....if you do.......remember a little goes a long way..... And, stay far from the pad surfaces and shiny parts.
On second thought, just clean everything with soap and water and call it a day.

Any thoughts on disconnect hubs and milage?

A side note: I owned a 1978 cj v-8 304 two barrel carb, t-18, 3.73 geared, 33X10.5 radial ss that consistantly returned 14-17 mpg uphill/downhill with or against the wind. Equal to or better than my stock TJ before cleaning the TJ brake system.

Next Phase
next year is to go 2" OME inch 33 X 10.5 radial SS and minimum B.L. to clear. Gear, Tranny, Motor Swap.
I am going for milage (shooting for 19-20mpg), streetability, and 10%-15% better off road function.
I have a 2002 5.3 GM LS truck motor and 4spd O.D. trans, stock Rubi (4.10) dana 44s for each end.....haven't decided on the t-case.

I know its all relative.....but every penny saved can be wasted somewhere else.....Right?

I wANt To bE DiffeREnT JusT LiKe EveRyOne eLsE!
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ehirner
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Joined: 01 Jan 2004
Location: Eastern PA

PostPosted: Fri Oct 27, 2006 1:20 pm    Post subject: Reply with quote

Those that have installed selectable hubs have reported no increase mileage. Good luck in your search for 20mpg in a Wrangler. 15 is about average. 10-12 if heavily modded for offroading.
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el_dubya
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Joined: 20 Sep 2005

PostPosted: Mon Oct 30, 2006 3:16 pm    Post subject: Reply with quote

Quote:
14-16mpg sea level-1500ft cheap gas..worse if I use 5th, I don't



I take this to mean you don't use 5th gear? I am going to assume it lugs the engine down to a point where it hurts mileage?
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TJ Apex
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Joined: 29 Jul 2005
Location: Mountains of SoCal. 6257 elev.

PostPosted: Wed Nov 08, 2006 9:13 pm    Post subject: Reply with quote

First off you said you have 31 inch tires, this means your speedo is not reading correctly. Your going faster that you think. And, your also going farther that your odom is reading, witch is giving you false info.
I have 32 inch tires, and with the use of my GPS, I found how far off my odom really was.
I went 10 miles according to my trip meter, then I looked at the trip on my GPS, it read 11.2, that means I went 1.12 miles farther. So when I do a mileage check, I'll take the trip reading and multiply it by 1.12, witch gives me my true miles traveled, then divided by gallons used, then I have true MPG.
I average 18.4 MPG, and I have almost gotten 21 MPG shifting when the "up shift light" comes on.
As far as miles indicated, I'll get anywhere from 230 to 242, again multiply 242 by 1.12=271.04 true miles, divided by 13.5gal.=20.07MPG.

As far as sticking calipers, that would give you bad mileage, but remember, the TJ is an aerodynamic barn and has a larger drag coefficient than a CJ, simply because the TJ's body it wider.

Just so you know, I found that I get better mileage with the top down, than I do with the top up and A/C on. I do use 5th gear, the lower the RPM the better, and I also drive 65-70 mph on the freeway.

I hope this info helps ya
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02' Apex Edition,
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330T
Member


Joined: 29 Sep 2006

PostPosted: Thu Nov 09, 2006 9:06 am    Post subject: Reply with quote

TJ Apex,

I assume you have a manual? What gears are you running?

I have a 03 and I'm thinking of putting 31 on it, but drive almost 70 miles a day to and from work. Right now i average about 17 to 18 mpg. I dont mind that but if is going to drop to 15 for get it
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Lowrider
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Joined: 08 Nov 2005
Location: Washington State

PostPosted: Thu Nov 09, 2006 9:23 am    Post subject: Reply with quote

"I went 10 miles according to my trip meter, then I looked at the trip on my GPS, it read 11.2, that means I went 1.12 miles farther. So when I do a mileage check, I'll take the trip reading and multiply it by 1.12, witch gives me my true miles traveled, then divided by gallons used, then I have true MPG."


If your speedo indicates 10 miles and your GPS indicates 11.2 miles then you actually traveled 1.2 miles further, not 1.12 miles.

Edit:
I guess you must be talking percentages. You traveled 12% further than your speedo indicated so you multiply your speedo miles by 112% (1.12) to get actual miles traveled.

Sorry for being so anal about the math. Mr. Green
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TJ Apex
Member


Joined: 29 Jul 2005
Location: Mountains of SoCal. 6257 elev.

PostPosted: Thu Nov 09, 2006 5:35 pm    Post subject: Reply with quote

Yes, I do have a 5 spd manual trans and my TJ is all stock except for a K~N cone filter and 32's. If I remember right the gears are 3:08's from the factory. I bought it used, so I don't know if someone changed the gears or not. I'll have to check that...

No need to feel sorry about being anal about your math, I'm a machinist, I'm anal about math everyday...anyway, My GPS reads in tenths of MPH and distance, so it was easy to do the math, but to answer your question, yes 12% would be correct.
I don't think having 31's would be much different, maybe 1-2% correction (1.1)

Yeah my bad 1.2 is right, I’m good at math and apparently not at typing
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Why do I have to press one for English?!
Welfare recipients should pass a drug test to get paid…

02' Apex Edition,
2" BB, 31" BFG AT's
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