MPG Help

[j99xj]

No problem.

It really works. You should see results immediately.

The best way to save money at the pump starts with you.

 

[scottbky]

Got a question. I've generally been eggshelling when I start from stop (driving like an egg between foot and accelerator). I've got a ScanGauge hooked up showing me generally instantaneous (~2 sec update) mpg. It occurs to me that I've been getting 9-10 mpg for 30 sec until I get to 60 mph or so. If I medium accelerate (not wide open), then I'm getting 7-8 mpg for 15 sec or so until 60. Any opinion on cumulative mpg? Will the lower mileage get compensated by getting to high mileage quicker?

ScottB

 

[wascdo]

I'm getting about 21.5 mpg on my trips to my parents house (about 5 hours and a mix between 20% city and 80%+ highway). My cherokee is a 96, has over 200,000 miles on it, and a torn out O2 sensor at the cat. I use 87 octane at the pumps and regularly change the oil. but i have yet to check the spark plugs or differential fluid in the 2 years i've owned her...........haha!!

 

[sandmcrew2]

I tend to dissagree with the statement that you should keep the rpms low, at around 2200. I drive a 98 4.0 manual with 4 inches of lift, armor all around, high lift, spare tire, and 32 inch all terrains on 3.55 gears. I never shift below 3000 unless there is absolutely no load on the engine, like going flat, accellerating very slowly, or going downhill. I regularly get on it pretty hard, but when Im not i drive to save gas. I tend to cruise at 2200 ish if there is no load, 2500-3000 with a load (ie: up a slight grade or more, even when going slow). Just cause you are revving it higher doesnt mean you have to be gettin on it hard (at least with a manual). Peak torque for my 98 is around 3k rpm, therefor why I shift there. I have tried shifting at lower rpms and it tends to bog (not really, but it is happier at higher rmps). And even with my 32's I am lower than stock with gearing with my 3.55 than with stock tires and stock 3.07's. My speedo still reads about 5% too high. I manage between 15.8-16.2 mpg very consistantly, with all city driving, and about 20 on the highway @ 2400 and 75 mph. BTW, traffic permitting, I always drive 10-15 over the speed limit. This is with california 87 octane, and stock exhaust. Only mods to the engine are a KN cone filter, TB spacer, and relocated AIT sensor. My jeep has 135k miles on original everything exept a walbro high output fuel pump (if anything, would REDUCE mileage), doesnt have a fresh tuneup, but I do change the oil very regularly. Just my .02, im sure some of you will dissagree, but just wanted to share my observations.

-Jerry

 

[rustysxj]

i just got my jeep tuned up and ive made the 14mpg to 17 mpg jump
wow did i have some gunk

 

[BBeach]

I tend to dissagree with the statement that you should keep the rpms low, at around 2200. I drive a 98 4.0 manual with 4 inches of lift, armor all around, high lift, spare tire, and 32 inch all terrains on 3.55 gears. I never shift below 3000 unless there is absolutely no load on the engine, like going flat, accellerating very slowly, or going downhill. I regularly get on it pretty hard, but when Im not i drive to save gas. I tend to cruise at 2200 ish if there is no load, 2500-3000 with a load (ie: up a slight grade or more, even when going slow). Just cause you are revving it higher doesnt mean you have to be gettin on it hard (at least with a manual). Peak torque for my 98 is around 3k rpm, therefor why I shift there. I have tried shifting at lower rpms and it tends to bog (not really, but it is happier at higher rmps). And even with my 32's I am lower than stock with gearing with my 3.55 than with stock tires and stock 3.07's. My speedo still reads about 5% too high. I manage between 15.8-16.2 mpg very consistantly, with all city driving, and about 20 on the highway @ 2400 and 75 mph. BTW, traffic permitting, I always drive 10-15 over the speed limit. This is with california 87 octane, and stock exhaust. Only mods to the engine are a KN cone filter, TB spacer, and relocated AIT sensor. My jeep has 135k miles on original everything exept a walbro high output fuel pump (if anything, would REDUCE mileage), doesnt have a fresh tuneup, but I do change the oil very regularly. Just my .02, im sure some of you will dissagree, but just wanted to share my observations.

-Jerry

With 32's and 3.55 gears and .79:1 O/D you should be doing 82mph at 2400rpm. Thats a lot of force you're going against with the heavy tires and the aerodynamics of a box. Drag is proportional to the velocity squared and most people get 20+mpg at 55-60mph. You'll have over double the drag at 80mph as someone at 55mph. Plus with the gearing and heavy tires all while doing it on the highway, and 20mpg...when every time I went 75+ I would get 16mpg with 235's (came with 225's orig). Im gonna be the first to call the :bs: . :dunce:

 

[BBeach]

I tend to dissagree with the statement that you should keep the rpms low, at around 2200. I drive a 98 4.0 manual with 4 inches of lift, armor all around, high lift, spare tire, and 32 inch all terrains on 3.55 gears. I never shift below 3000 unless there is absolutely no load on the engine, like going flat, accellerating very slowly, or going downhill. I regularly get on it pretty hard, but when Im not i drive to save gas. I tend to cruise at 2200 ish if there is no load, 2500-3000 with a load (ie: up a slight grade or more, even when going slow). Just cause you are revving it higher doesnt mean you have to be gettin on it hard (at least with a manual). Peak torque for my 98 is around 3k rpm, therefor why I shift there. I have tried shifting at lower rpms and it tends to bog (not really, but it is happier at higher rmps). And even with my 32's I am lower than stock with gearing with my 3.55 than with stock tires and stock 3.07's. My speedo still reads about 5% too high. I manage between 15.8-16.2 mpg very consistantly, with all city driving, and about 20 on the highway @ 2400 and 75 mph. BTW, traffic permitting, I always drive 10-15 over the speed limit. This is with california 87 octane, and stock exhaust. Only mods to the engine are a KN cone filter, TB spacer, and relocated AIT sensor. My jeep has 135k miles on original everything exept a walbro high output fuel pump (if anything, would REDUCE mileage), doesnt have a fresh tuneup, but I do change the oil very regularly. Just my .02, im sure some of you will dissagree, but just wanted to share my observations.

-Jerry

With 32's and 3.55 gears and .79:1 O/D you should be doing 82mph at 2400rpm. Thats a lot of force you're going against with the heavy tires and the aerodynamics of a box. Drag is proportional to the velocity squared and most people get 20+mpg at 55-60mph. You'll have over double the drag at 80mph as someone at 55mph. Plus with the gearing and heavy tires all while doing it on the highway, and 20mpg...when every time I went 75+ I would get 16mpg with 235's (came with 225's orig). Im gonna be the first to call the :bs: . :dunce:

 

[Stumpalump]

With 32's and 3.55 gears and .79:1 O/D you should be doing 82mph at 2400rpm. Thats a lot of force you're going against with the heavy tires and the aerodynamics of a box. Drag is proportional to the velocity squared and most people get 20+mpg at 55-60mph. You'll have over double the drag at 80mph as someone at 55mph. Plus with the gearing and heavy tires all while doing it on the highway, and 20mpg...when every time I went 75+ I would get 16mpg with 235's (came with 225's orig). Im gonna be the first to call the :bs: . :dunce:

32" tires dont ride at 32" for your math so he may be right. I also agree that not lugging the engine will save gas because the engine will be at a much higher vacuum. Using a vacuum guage to learn at what laod and RPM's give the highest vacuum would be a good way to learn what your rig likes.

 

[BBeach]

32" tires dont ride at 32" for your math so he may be right. I also agree that not lugging the engine will save gas because the engine will be at a much higher vacuum. Using a vacuum guage to learn at what laod and RPM's give the highest vacuum would be a good way to learn what your rig likes.

I did a calculator online this morning and it said he'd need to run 29.5" tall tires to get those effects. I just cant see a lifted jeep with 32's, 3.55 gearing, no "fresh" tuneup getting 20mpg on the highway at 75mph, whereas my stockish jeep can barely get 20mpg only when doing 55-60 and once I get up to 75mph its 16mpg. How exactly do you know you're getting 20mpg? Any consistency or was that just one lucky fillup?

 

[Stumpalump]

29.5 may be right because the tire may not be new and the tire squishes. To find the right number you must measure from the ground to the center of the axel then double it. I agree 20 mpg sound high. I was like 13.5 with my 31's but a 31 will travel farther than the odometer reads so it was probably closer to 14 or 15 mpg. Woo hoo! These things just suck fuel like a fein.

 

[ZacSquatch]

I'm gettin 23 hwy, 31.6's, 3.55's, and I cruise it around 2000-2200 (65-80)

I also took a steel pipe through my cat... busted the sucker out and made it hollow.

 

[MaXJohnson]

29.5 may be right because the tire may not be new and the tire squishes. To find the right number you must measure from the ground to the center of the axel then double it. I agree 20 mpg sound high. I was like 13.5 with my 31's but a 31 will travel farther than the odometer reads so it was probably closer to 14 or 15 mpg. Woo hoo! These things just suck fuel like a fein.

for a correction factor, you can figure 3% to 5% loss for rolling radius. Closer to 5% for larger, softer offroad type tires. With that in mind, his 75 MPH cruising speed is closer to 71 MPH and his calculated MPG is more like 15 city and 19 highway. This is closer to what you would expect, but still a little high. Using the 5% correction, his 32" tires, .79 OD and 3.55 gears at 2400 RPM would calculate out to more like 77.4 MPH.

The undeniable factor that kills gas mileage, like BBeach mentioned is the huge increase in drag with speed.

 

[BBeach]

I'm gettin 23 hwy, 31.6's, 3.55's, and I cruise it around 2000-2200 (65-80)

I also took a steel pipe through my cat... busted the sucker out and made it hollow.

So 2200rpm, you're 10% higher than 2000rpm. 110% of 65mph is a little over 70mph, you're more off than the last guy haha.Your speedo must be way off...:bs: