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Discussion Starter · #1 ·
I understand that owning my Jeep means bad gas mileage but after talking to a bunch of people something just isn't right. I get about 10mpg in my 89 Wrangler, here are the specs, 32" BFG MT's, Chevy 350(bone stock), fuel supplied by a Edelbrock Quadrajet topped with a 14x3 K&N,Heddman headers with 2 1/4" dual exhaust with flowmaster mufflers,flex-a-lite electric fan, a Turbo 350 tranny(built with heavy duty clutch packs), stock transfer case(NP231) and stock axles front and rear(d30 front and 35 rear) with stock gears, 3.05 I believe...not sure. Anyway my old 258 got horrible gas mileage and I had everything checked on it and was in the shop many times and they couldn't find the problem. I installed a Weber Carb and it made NO difference. So finally I went with a Chevy 350. Like I said I know not to expect great gas mileage but I know people with Suburbans that have a 350 and they get better gas mileage than me??? The only thing that is left from the old engine is the radiator, how could this affect gas mileage?? Even if I could get the number up to around 12 to 13mpg that would be fine with me. One thing that I have noticed is that the engine runs VERY cool. On my temp gauge(which I know for a fact works correctly) the engine barely gets up over 2nd dash on the stock YJ gauge. So I am guessing that engine runs at about 150-160, that seems a little cool to me. Anyone got any suggestions????? I am stumped.

absolutjeep
 

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/wwwthreads_images/icons/tongue.gif you need to treat your SB Chevy to a 190 degree thermostat with a tiny hole drilled in it of course. These modern engines need more heat to run well. There is no earthly reason why you should get that poor fuel mileage unless you are dumping fuel out on the road. Also DO check and make sure that your front drive isn't in all the time. With 3.05's, and 32's, you should have to stop every now and then and DRAIN the gas to keep the tank from running over it would get such good fuel mileage that it would put gas back in the tank./wwwthreads_images/icons/crazy.gif How about the return line to the tank? Is it still functional? What about the emissions equipment; is it set up correctly? How about the ignition? Is it an HEI and does it have the correct advance? You need to slove this problem because if the Democrats remain in the White House; OR if the Dirtbag finds an excuse to declare martial law so HE can stay in there; you will need good fuel economy to stay ahead of the UN forces which will be in here trying to eliminate all off-road vehicles because that makes you too "independent" and therefore an "enemy of the state" If you can get that MPG up to the mid teens, you will have to steal a lot less gas to keep going, and keep one step ahead of the Clintonoid Commie Ninja Pcs of crap who are trying to subdue you and all the rest of us "independent" non-Geo Metro drivers./wwwthreads_images/icons/crazy.gif

CJDave
 
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Discussion Starter · #3 ·
How fast are you driving when you get this milleage? Remember you are pushing something as areodynamic as a piece of plywood down the road. I would try a profesional tune up. My four banger gets 12 or 13 consistantly and I have a habit of being a lead foot. My only other idea is that your odometer might be off. The bigger tires will through a stock speedo and odometer off. Mine is off by ~20%. If I don't factor this in when I check my mileage, it drops to 10mpg. Sorry I can't be more helpful,

Nick Hagen
1995 Wrangler
33" Mud Tires and a four banger
 
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Discussion Starter · #4 ·
Hey Nick I drive normal speeds up to about 75mph. Do a good mix of driving, some highway some around town. I know it's like pushing a brick but like I said in the first post, I have friends with Suburbans with the same engine and they get 5-6mpg better than I do. That is the only reason I am asking. I am going to the parts store after class/work today to pickup a new thermostat. I think that that could be my problem.

absolutjeep
 

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Official Curmudgeon
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4,707 Posts
You've got a lot more than the radiator left from the 258. There's 2 axles, 4 sets of brakes, wheel
bearings and the t-case. Pick a long flat paved road and get the Jeep up to 30 then put it in neutral.
How far does it roll? If it feels like the brakes are partially applied start checking. How much air
pressure in the tire? Do you have lockouts on the front axle? How about front end alignment? I'd get
rid of the Quadrajet, but that's just me, but check to make sure the secondaries are closed. Maybe it's
just your driving style. I've got a 305 TPI in an '80 CJ and I get 18-20 MPG without correcting for the
oversized 31" tires and I have a heavy foot.


 
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Discussion Starter · #6 ·
Okay, a few things come to mind here. A Suburban is more stream lined that that Jeep. Also, that tranny doesn't have over drive, and depending on the year- the burbs might. Also, did you regear the speedo? That tire change from the stock 28" will throw you off there.

_____________________
John
95.5 YJ with "stuff"
http://SonsofThunder4x4.com
 
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Discussion Starter · #7 ·
Some VERY good points CJTaz I am actually replacing the axles in less than a month. I will try the neutral test sometime this week, we just got our first snow here in NY so I have to wait till that gets off the roads. FNG I did know that I don't have overdrive but I didn't think it would make that big of a difference. And also no the speedo isn't corrected for the 32" tires but I figured that my speedo is about 10% off. Well I am going to get a new Thermostat right now(190 deg) since the part is only 8 bucks I figure I will try that first. Thanks for all the help and anyone else with ideas feel free to add them.

absolutjeep
 

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Official Curmudgeon
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Hey, even if the thermostat doesn't help with the gas mileage, at least you'll be warmer in that snow.


 
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Discussion Starter · #10 ·
To get a good baseline on how far your speedometer is off I would use the mile signs on the side of most interstates highways. If you
have never done this then this is how it works. Find a good time of the day when you will be able to drive at exactly 60 speedometer
mphs for a full mile without having to slow down because of traffic. You will need a watch with a second hand, and perferably a
co-pilot to work the watch. First get you jeep going exactly 60mph according to your speedometer. At the exact time you pass a
mile post start your stop-watch or note where the second hand is. Maintain the before mentioned speed until you reach the next
mile post. At this mile post stop the stop-watch or again record the location on the second hand. Now that you have the total
elapsed seconds for each mile driven you can find your actual speed. This is the equation:
actual mph=60/seconds between mile posts.
So if say it took 75seconds to travel one mile by the mile posts you have:
0.8=60/75
This means that for every mile on your speedometer you actually only travel 0.8miles.
Good Luck,
Ethan

 

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Official Curmudgeon
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4,707 Posts
There are two things wrong with your advice Ethan. First, mile posts are not that accurate, try about 5
miles or more to get a good reading. Second, the speedometer and the odometer are not neccesarily
that closely related. The speedometer could be off by quite a bit while at the same time the odometer
is quite accurate especially with worn springs, magnetic loss and or mechanical binding of the needle.


 
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Discussion Starter · #12 ·
You have some good points there CJ7Taz. Basically the more miles posts you use to measure with the more accurate you results
will be as one oddball measurement will have less effect on your results. If you can travel for five miles at a constant speed then you
just have to add up the total number of second from the first mile post to the fifth, and then replace the 60 that was the constant in
the one mile test, with 300 for the five miles. If you can't go at a constant speed for that far in one stretch then just take five seperate
one mile test and average them.
(t1 t2 t3 t4 t5)/5=average number of seconds for each mile post
Then you would just plug that into the first equation with 60 as the constant.

As far as the odometer vs. the speedometer there can be some variation in the data they show. The odometer reading will usually be
the more accurate of the two though, as the cable goes directly into the gear box that is the odometer. The speedometer in most
cases uses a turning magnet to pull the speedometer needle. The faster the rpms of the magnet the higher the speedometer shows.
The magnet can loose magnetism, the case that the parts can loosen, resistance to the needles movement can increase or
decrease, etc... If there is a large difference though it means parts are going bad.
The test method I previously talked about is best suited for testing the speedometer. If you want to test the odometer I would
suggest that you again drive down the interstate, but this time the speed does not matter. At your first mile post look to find the
milage as accurately as it is displayed. At the second mile post again look at the milage. What you want is the distance that your
odometer is showing you have traveled. The equation would go like this.
(totalnumber of miles as determined by the mile posts)/(total number of miles traveled as determined by your odometer(milage))=(the
number of miles you will have traveled for every mile shown on your odometer)
1/0.8=1.25 For every 1 mile traveled according to the odometer you have really traveled 1.25 miles.
When checking the accuracy of the odometer I suggest that you a lot more then one mile to check it. I would go aim for around
25 miles to get a relatively accurate result.
Sorry this post got so long, I just don't have a short way to describe how to do this.
Good Luck,
Ethan


 
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Discussion Starter · #13 ·
actually to get my 10% number I had a brand new TJ drive on one side of me and a brand new expedition on the other side of me..on the CB we talked to each other at various speeds and that is how I got the 10% number.

absolutjeep
 
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Discussion Starter · #14 ·
I agree with Dorfs... check your timing and play with that advance.

LarryM
85 CJ7, 350TBI ,T19 4spd
'00 TJ Sport, NV3550 5spd, D44, Teraflex system
 
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