[Blue84JeepCJ7]

Lets start over here. I am sorry I did not give proper information. Thanks for setting me straight!

Ok, first I do not care if I get bad gas mileage or good gas mileage. If I was concerned about gas mileage I will ride my motorcycle or go buy a Geo Metro! I have been driving my 97 TJ for 10 years @ 14 mpg!

The below is for my 84 CJ-7

I am still trying to figure out what I have in this thing. So far all I know is that it is a Chevy 350(325hp), mild cam with what may be a 4L80-E transmission which incorporates two overdrive gears.

So far I seem to get 12.1 mpg hwy at 55 mph. The second overdrive gear does not kick in until about 65mph. I have yet been able to check that part for mileage until I can get on the four lane hwy and kick it on up.

Now, I am happy with 12.1 However, I dislike the the 35" Cooper ATs and have ordered some 32x11.50 Cooper STTs. I also am looking for a hard top. I figured this may increase mileage a little. It appears that I have stock axles and more than likely stock gears.

Now my TJ has a I-6, stock gears 3.08, bad I know, and 33x12.50 Cooper STTs. 55 mph I get about 16 mpg. Interstate driving is slow at 60 if the wind is not blowing and only gets about 14 mpg. I know, been doing this for 10 years and the gears needed to be changed ten years ago. The pic to the left in my avtar was taken ten years ago, maybe 8 or 9....you get the hint, when I got the Jeep.


Sorry I failed to give proper info and ask the correct questions.

[Dmcastino]

There are way too many variables in your question. What gearing does the Jeep have? Is this city or highway? Is the driver heavy on the gas pedal? What v8 are we talking about here? There is a lot that can effect gas mileage, so it can be kind of difficult to accurately estimate it.

[GOLENJEEPTJ]

X2^, but even with smaller size tires.... it will still be nothing to write home about!

[yellojeeper]

If you have a lifted jeep with big tires and a V8, why in the world would you start worrying about gas mileage? Buy a Prius if that is your goal.

[Blue84JeepCJ7]

Auto overdrive.
In third gear it gets 10.1 mpg hwy, in overdrive it kicks in another gear at 55mph @12.1 mpg hwy. There is one more gear at about 65 but I haven't been able to try that one for mileage yet.....lol

Hardtop is next on my list!!

[BlueFlame]

Way too many variables - the question is too simple.
Type of tires, inflation pressures, axle gearing, transmission, how the engine is built and how it's tuned, driving style (ESPECIALLY driving style,) weight, accessories such as roof racks, etc all factor. I get mid 16s with 35s on a stock 4.0 for example. Others get less than 10.

In normal driving without a leadfoot an average V8, geared correctly (and with a decent transmission - as in, not an old school turbo350 w/ non locking converter,) should be able to return better gas mileage than the 4.0.

[BlueFlame]

Originally Posted by 97JeepTJ33

Auto overdrive.
In third gear it gets 10.1 mpg hwy, in overdrive it kicks in another gear at 55mph @12.1 mpg hwy. There is one more gear at about 65 but I haven't been able to try that one for mileage yet.....lol

Hardtop is next on my list!!

Turbo 400 with overdrive? How's that work? Do you mean it's a 4L80E?

From your description, 3rd gear, then overdrive, okay but what's with "one more gear at about 65" ? That would make it a 5 speed. And if it's not going into top gear until 65, something isn't right, either the kickdown cable is out of whack or the gearing is way wrong!

[Blue84JeepCJ7]

Originally Posted by BlueFlame

Turbo 400 with overdrive? How's that work? Do you mean it's a 4L80E?

From your description, 3rd gear, then overdrive, okay but what's with "one more gear at about 65" ? That would make it a 5 speed. And if it's not going into top gear until 65, something isn't right, either the kickdown cable is out of whack or the gearing is way wrong!

Thats pretty much what I am trying to find out with this thing!!!
Turbo 400 with five gears? Heck I don't know. My hobby for the past twenty years has been airplanes, not cars...lol I'm learning!

Original or not the overdrive has a manual switch on the dash. At 45mph I hit the switch and it changes into "fourth" gear. At about 60-65 it will change into fifth. Maybe it is a 4L80-E. I'll take a look at the oil pan and see if it resembles that state of Texas!

This thing is suppose to have 325hp, which it very well could be. It has 35"tires which I don't like. It drives real nice though!!!!

Also how can I tell which axles I have. I took a quick look and I see no numbers or letters anywhere.

[TXjeepTJ]

w/ 35's I get 17-20mpg highway(with a/c on too) and about 14 city (automatic 4.10 gears)

[Prot]

You need to go to the autoparts store and ask to see the transmission pan chart that is put out by whatever brand of transmission filters they carry.

TH400 and TH400 are three speeds and are commonly referred to as turbo 350 and turbo 400 transmissions. 4L60E, 4L80E, and 700R4 transmissions are four speeds, with the fourth gear being overdrive. All five of these are GM transmissions.

You are driving a four wheel drive vehicle that has 35" tires and you are concerned about fuel economy?

While you are at the parts store, ask to see the differential gasket picture section of their gasket book. Find the two that look like yours and have the same number of bolt holes.

Another thing you can do is post pictures of your transmission pan and differential covers and I am sure forum members will be able to identify all three pieces for you.

[Blue84JeepCJ7]

Who said I was concerned? Why is it every time someone ask about gas mileage it has to be stereotyped that it is a concern? Who out there doesnt want to get the best gas mileage they can get without it being a concern?


Thanks for the gasket info and differential info...I'll check it out!!

[Prot]

Apparently YOU are concerned since this thread IS about gas mileage. It is extremely difficult for people to help you and answer your questions if you don't even know what you are driving because you are descrbing a turbo 400 transmission that has more gears than it should. Then people ask fir more information in order to help you determine what you have so that a determination can be made if something is wrong and a reasonable estimate of fuel economy given, and you get upset about it. So, based on what we may assume might be accurate such as having a 350 Chevy engine and 35" tires, the answer to your fuel economy question is somewhere between sucky fuel economy and extremely sucky fuel economy.

I thought reasonable questions were asked about your setup. Considering it is far from stock, it is not an unreasonable request.

Your gear ratio will play an important roll in your fuel economy as well, so that is more information that needs to be provided. Is your speedometer accurate? Have you verified it with GPS? If your speedometer is wrong, your odometer is wrong as well, which will throw your fuel economy calculations off.

Last year when gas was $4/gallon the forum got flooded with fuel economy threads to the point where mods had to intervene.

[Blue84JeepCJ7]

Originally Posted by Prot

Apparently YOU are concerned since this thread IS about gas mileage. It is extremely difficult for people to help you and answer your questions if you don't even know what you are driving because you are descrbing a turbo 400 transmission that has more gears than it should. Then people ask fir more information in order to help you determine what you have so that a determination can be made if something is wrong and a reasonable estimate of fuel economy given, and you get upset about it. So, based on what we may assume might be accurate such as having a 350 Chevy engine and 35" tires, the answer to your fuel economy question is somewhere between sucky fuel economy and extremely sucky fuel economy.

I thought reasonable questions were asked about your setup. Considering it is far from stock, it is not an unreasonable request.

Your gear ratio will play an important roll in your fuel economy as well, so that is more information that needs to be provided. Is your speedometer accurate? Have you verified it with GPS? If your speedometer is wrong, your odometer is wrong as well, which will throw your fuel economy calculations off.

Last year when gas was $4/gallon the forum got flooded with fuel economy threads to the point where mods had to intervene.

I am going to get that info as soon as I can figure out what the Jeep has. Its not as easy to give the info since I may have not been given the proper info.

Listen, I I have been driving a 97 TJ for 10 years 50 to 80 miles per day at 14 mpg. I am not concerned ok!
The question was for my CJ, I wont get the Jeep back until Monday afternoon. As soon as I get it back I will check more and try to pinpoint what in the blazex I have...

I will go rename this post!

[Blue84JeepCJ7]

Lets start over here. I am sorry I did not give proper information. Thanks for setting me straight!

Ok, first I do not care if I get bad gas mileage or good gas mileage. If I was concerned about gas mileage I will ride my motorcycle or go buy a Geo Metro! I have been driving my 97 TJ for 10 years @ 14 mpg!

The below is for my 84 CJ-7

I am still trying to figure out what I have in this thing. So far all I know is that it is a Chevy 350(325hp), mild cam with what may be a 4L80-E transmission which incorporates two overdrive gears.

So far I seem to get 12.1 mpg hwy at 55 mph. The second overdrive gear does not kick in until about 65mph. I have yet been able to check that part for mileage until I can get on the four lane hwy and kick it on up.

Now, I am happy with 12.1 However, I dislike the the 35" Cooper ATs and have ordered some 32x11.50 Cooper STTs. I also am looking for a hard top. I figured this may increase mileage a little. It appears that I have stock axles and more than likely stock gears.

Now my TJ has a I-6, stock gears 3.08, bad I know, and 33x12.50 Cooper STTs. 55 mph I get about 16 mpg. Interstate driving is slow at 60 if the wind is not blowing and only gets about 14 mpg. I know, been doing this for 10 years and the gears needed to be changed ten years ago. The pic to the left in my avtar was taken ten years ago, maybe 8 or 9....you get the hint, when I got the Jeep.


Sorry I failed to give proper info and ask the correct questions.

[Prot]

Here is what I think you have. You probably have either a 700R4 or 4L80E transmission. Behind that transmission you probably have an additional overdrive unit. They were popular in the JC Whitney catalogs years ago.

Is your speedometer/odometer correct for the tire size you are running? Verify it with GPS.

The hardtop will get you a couple of mpg's at the most. If fuel is the sole reason for purchasing a hard top, I'm not sure it would be worth it. On the other hand, hard tops are quieter, more secure, etc. so in that regard they are worth it. I never put my softop on. It's always my hard top, with or without the t-tops on.

What exactly do you dislike about the 35" Cooper AT's? Have you experimented with tire pressure and did the chalk test?

Here's some fuel economy figures from my 07 JK with the infamous 3.8L minivan engine.

bone stock with 32" street tires and stock 4.10 gears I got 19 mpg
switched to 35" BFG AT tires and kept stock gearing and got 12 mpg
regeared my differentials to 5.13 and kept same tires for 17 mpg

You have a completely different Jeep and drive train, but I am just demonstrating variables here, particularly when it comes to gearing.

I think sometimes on emails and online forums, intent gets lost since there is no tone of voice to judge by. I am sure no one here intended any malice.

That CJ of yours sounds pretty cool, minus the body lift of course. I've never been a fan of body lifts, but to each his own. Hey, at least you aren't driving a Jeep with a minivan engine.