trans question

225/75R15s are 28s 2700rpm at 50mph.
31s drop the rpm to about 2450rpm.
33s... about 2250rpm.

Go here to play with tire/gear/tranny combinations
http://www.grimmjeeper.com/gears.html

I think you have 4.56 gears to get 2700rpm with 28s at 50mph.
With the SE 4cylinder you need more rpm than the 4.0L
I think your mileage problem might not be related to driveline. I'd spend more time on tuning.
 
johnny said:
Also, you need to drop the tank and see if it has the 15 or 19 gallon tank. The difference is the length of the filler tube inside the tank being longer to limit the fill level to 15 gallons. If so, you can cut it off using one of the various methods documented online to achieve the full 19 gallon fill capacity
so how do I go about doing this or finding it out online
Click to expand...

Run it until it's almost empty on the gauge. Then go to fill up. If you fill up and it takes more than 15 gallons (which it will if you're on empty) then you have the 19 gallon tank.
 
  • Like
Reactions: Serbonze
so 150miles/12gallons.... about 12.5mpg. Will you ever get that elusive EPA 17mpg?? None of us do.
Yer Jeeps almost 20 years old but yeah there is room for improvement. 14/15 should be doable. In the summer. On flat ground. Without constantly flooring it.

"will bigger tires drop gas milage or go up in milage"

Bigger tires will drop the rpm at any given speed.
Same thing an OD transmission does... but lots cheaper/easier.
will an OD transmission give better mileage?

There are other variables... 31s/32s/33s will also be wider and heavier.
And maybe with the SE you need 2700rpm at 50mph.
I don't think your mileage issues are gearing related.
More likely tuning, sensors, injectors, .....
Maybe even driving style??????
 
billiebob said:
I don't think your mileage issues are gearing related.
More likely tuning, sensors, injectors, .....
Maybe even driving style??????
Click to expand...

X2

I think it's either this or maybe you have the smaller 15 gallon tank in which case the miles you get per tank is going to be less than if you had a 19 gallon tank.
 
I've got a '99 SE with a 5 speed. 27" tires. As much as I know, all '99s have a 19 gallon tank. With all of that being said, the best gas mileage that you can expect is about 17 - 18 mpg. Try to keep the rpm's around 2700 to 3200 rpm's. When you are cruising, be light on the throttle. Accept that in the real world the 4.0 six will get better mileage on average than the four will. Oil changes and tune ups are imperative. If you can squeeze 18 mpg out of an SE, consider yourself lucky.
 
You'ld think. But the reality is that the six is a better match in the TJ to the real world than the the four. A small, high torque V-8 would have been ideal.

Sent from my SM-G900V using Tapatalk
 
Chris said:
Funny... Because you'd think the 4 banger would get better mpg than the 6, right
Click to expand...
You'd think but it has to be driven so much more aggressively to keep up with traffic than the 4.0L does that it pretty much loses its much of its potential for better mpg.
 
  • Like
Reactions: StG58
Jerry Bransford said:
You'd think but it has to be driven so much more aggressively to keep up with traffic than the 4.0L does that it pretty much loses its much of its potential for better mpg.
Click to expand...

That was my thought. You have to keep it revved so high to move such a heavy weight, that it loses any efficiency it would otherwise have as far as gas mileage is concerned.

Makes you wonder what in the hell Jeep was thinking even putting out a 4 cylinder in the first place.

Back in the day I had a 87 Cherokee 4 cylinder and that thing was an absolute dog on the highway, it could barely make it up to speed to pass anyone.
 
Back in the 1980s we had 2 Chevy pickups... A '78 1ton with a 454, an 11' camper and towing a ski boat....and an '82? 1/2 ton with a 305 and a 8' camper. Every gas stop the 305 took more gas than the 454.
 
  • Like
Reactions: Chris
Chris said:
That was my thought. You have to keep it revved so high to move such a heavy weight, that it loses any efficiency it would otherwise have as far as gas mileage is concerned.

Makes you wonder what in the hell Jeep was thinking even putting out a 4 cylinder in the first place.

Back in the day I had a 87 Cherokee 4 cylinder and that thing was an absolute dog on the highway, it could barely make it up to speed to pass anyone.
Click to expand...

Once you look up and understand CAFE, it all begins to make more sense. It has little to do with Jeep but more to do with the Corporate Average Fuel Economy. If you build 50 Dodge Vipers, you need to build 10,000 4 cylinder Jeeps that on paper look to have a higher average fuel economy to stay within the Federal guidelines when you average in the Viper mileage.
 
Top Bottom
Back