Better MPG?

[Krazors001]

Am i missing something? Why cant i find throttle body spacers for 90 and earlier?

https://rustysoffroad.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=rustys&Category_Code=PER_AIR the tbs25.

 

[MaXJohnson]

Any belt driven accessory costs horsepower and mileage, every last one of them. Water pump, alternator, power steering, fan, and certainly the a/c (when on). They all have mass that must be accelerated along with the rest of the drivetrain when the rpms pick up; not to mention the energy they suck up to do the work they were designed to do. Reducing this mass, and what is called the "moment of interia" in physics will save energy for moving the car instead of the accessory. Thus the mileage increase.


The only accessory that is practical to get rid of on a street driven Jeep is the belt fan. I just leave my a/c off 75% of the time because I know what a drain it is. I actually turn my a/c ON when going down steep hills on the trail and highway because it helps with engine braking quite a bit.

The impact on fuel mileage due to the "moment of interia" of the fan is so low that it is meaningless to this discussion. If you have calculations or information to the contrary, it would be interesting to see. During highway cruise, fan RPM is relatively stable, so the "moment of inertia" does not apply. During normal street driving, it is likely that your Jeep is in an accelerating mode less that 10% of the time.

The mileage penalty due to the fan is mainly from the work performed; pushing or pulling air.This has an impact on fuel mileage, but so does the increased drag on the alternator attributed to an electric fan. When you replace the engine driven fan with an electric, both have inertia to overcome and both require energy to push or pull the air. The electric fan is typically lighter and slightly more efficient. The savings in fuel is not the total drag of the engine driven fan, but the difference between the two.

Drag racers realize a gain in power by switching to an electric fan, water pump, etc. but they are running off battery power which is recharge after the run. We have to constantly replace the power consumed by electric accessories. There is no free lunch.

 

[seanof30306@yahoo.]

Any belt driven accessory costs horsepower and mileage, every last one of them. Water pump, alternator, power steering, fan, and certainly the a/c (when on). They all have mass that must be accelerated along with the rest of the drivetrain when the rpms pick up; not to mention the energy they suck up to do the work they were designed to do. Reducing this mass, and what is called the "moment of interia" in physics will save energy for moving the car instead of the accessory. Thus the mileage increase.


The only accessory that is practical to get rid of on a street driven Jeep is the belt fan. I just leave my a/c off 75% of the time because I know what a drain it is. I actually turn my a/c ON when going down steep hills on the trail and highway because it helps with engine braking quite a bit.

Regardless, my point is simply thet there is no way you'll see a 1.5mpg gain from switching to an electric fan. You realizing you're talking between an 8 and 10% increase on most XJs? No way.

 

[kleake]

I have to agree that the gains people are seeing are that big... I get about 16-17 mpg with mostly highway driving... I know I could get better if I lighten my foot,,, but I have a hard time doing that... I do find it hard to believe someone getting over 20 out of an xj,,,, wonder if everyone is figuring it their gearing and such correctly.

Does anyone know what the XJ's were rated from the factory?

On a side note, my dad went from an XJ to a Toyota Prius a couple of years ago. He now has almost 50K on it in the 2.5 years and went from 18mpg up to 51-52.... The car cost him about 25K, which at the time a comparable Camery was going for just about 22-24K so the price increase wasn't that bad... And until you ride and drive one,,, they do look funny and seem like you are losing so much... This thing is every bit as fast as the XJ, has traction control, GPS navigation, fully electronic everything... Very impressive how much is in the car for the price, and to see he can get close to 600 miles out of his 11 gallon tank is pretty good....

XJ 300 miles at $3 gallon = $53.... Prius 300 miles at $3 gallon = $18..... hmmm,,, $35 savings... Considering I fill up almost twice a week, that would save me $280 a month in fuel, almost a car payment!.. And, there is one more thing you have to consider.... You may only save $1000 per year out of pocket, but if you are putting it in the pump it's gone forever, if you are putting towards a vehicle,, you will at least be investing it and getting some of it back when you sell the car.... I understand the value of the car will go down considerably,,, but at least you do get something back,, unlike trying to sell your used fuel.....

 

[j99xj]

Fans aren't needed (either type) when the vehicle is moving forward at a moderate to fast speed. There is more than enough air rushing past the radiator/engine from just the motion of the vehicle itself.

The stock belt fan runs ALL the time, when it is needed or not.

The electric fan is only run when needed if you hook it up in tandem with the stock electric fan. (slow speeds around town, rock crawling, etc.) It shuts off completely once the vehicle speed increases and the "ram air" effect takes over. This is where most of the mileage gain is found. The other part of the mileage gain (as stated before) is from the omission of the shear mass of the stock belt fan. (The moment of inertia arguement that I said earlier is valid.)

Running a belt fan when it is not needed, is like sleeping with the lights on. It just doesn't make sense.

 

[MaXJohnson]

Fans aren't needed (either type) when the vehicle is moving forward at a moderate to fast speed. There is more than enough air rushing past the radiator/engine from just the motion of the vehicle itself.

The stock belt fan runs ALL the time, when it is needed or not.

The electric fan is only run when needed if you hook it up in tandem with the stock electric fan. (slow speeds around town, rock crawling, etc.) It shuts off completely once the vehicle speed increases and the "ram air" effect takes over. This is where most of the mileage gain is found. The other part of the mileage gain (as stated before) is from the omission of the shear mass of the stock belt fan. (The moment of inertia arguement that I said earlier is valid.)

Running a belt fan when it is not needed, is like sleeping with the lights on. It just doesn't make sense.

ya got that "shear mass" calculated yet???

do ya think that "ram air" effect might make the fans job a little easier???

 

[j99xj]

ya got that "shear mass" calculated yet???

do ya think that "ram air" effect might make the fans job a little easier???

1. Dr. Dyno says the belt fan is 5 lbs. I believe him.

2. Why yes, thats the entire point of an electric fan. If we utilize the "ram air" effect at moderate to high speeds, the fans job is easier because its simply not running, thus the engines job is easier (doesn't have to drive it), thus you save gasoline!

If you believe the "ram air" effect makes the fans job easier, you MUST believe the electric fan saves gasoline! And that figure is about 1.5 mpg.

I don't know if you being a smart ass or just plain stupid, I can't explain this any more clearly.

 

[XJBANKER]

i've got 33's with 4:56 Gears and can leave layton utah and arrive in Moab on 1 tank of gas. As long as I can get to moab I am happy. I am too excited to stop anywhere on the way. Stopping the Jeep on its way to Moab is like stopping a dog without a leash from chasing a stray cat. It knows what it wants and it is going to get it.:soapbox:

 

[seanof30306@yahoo.]

Fans aren't needed (either type) when the vehicle is moving forward at a moderate to fast speed. There is more than enough air rushing past the radiator/engine from just the motion of the vehicle itself.

The stock belt fan runs ALL the time, when it is needed or not.

The electric fan is only run when needed if you hook it up in tandem with the stock electric fan. (slow speeds around town, rock crawling, etc.) It shuts off completely once the vehicle speed increases and the "ram air" effect takes over. This is where most of the mileage gain is found. The other part of the mileage gain (as stated before) is from the omission of the shear mass of the stock belt fan. (The moment of inertia arguement that I said earlier is valid.)

Running a belt fan when it is not needed, is like sleeping with the lights on. It just doesn't make sense.

Nobody's arguing those points, dude. The point that sticks is that the fan is costing 1.5 mpg. Now, you're making an emphatic statement, and you're arguing it's true when others are skeptical; yet you have no data to back it up.

I can comfortably say the throttle body spacer and removing the silencer are NOT worth the 1.55 mpg you said they are. I've done them on my car and saw no change.

As far as the fan goes, I haven't done it on my Jeep, but I have done it on another car, with a MUCH bigger fan (and therefore much more drag from that fan), and saw nowhere near the 1.5 mpg increase you're insisting on. Now, if you're going to argue the point, then come back with some DATA: go drive a 60 mile course with the fan on, then pull the fan and drive it again, recording the mileage both ways. Even as hot as it is, if you do it at night, it won't be an issue. If you're not willing to back your s*it up with actual testing, then you need to just be quiet.

On another subject, how about using a vacuum gauge to help alter driving style? The more throttle you use, the lower the vacuum drops, right? You could put a vacuum gauge in a pod and watch it to see where your foot's the heaviest, then working on taking the lead out.

 

[MaXJohnson]

...I can't explain this any more clearly.

Apparently not.

At this point, I can return your personal insults, or assume that you don't have the depth of knowledge to back up what you've read on the internet

 

[BrettM]

take it easy on the gas pedal. it's proven, and free.

 

[MaXJohnson]

take it easy on the gas pedal. it's proven, and free.

as well as the pedal on the left; designed to turn kinetic energy into heat

 

[j99xj]

On another subject, how about using a vacuum gauge to help alter driving style? The more throttle you use, the lower the vacuum drops, right? You could put a vacuum gauge in a pod and watch it to see where your foot's the heaviest, then working on taking the lead out.

It's a good idea that Jeep thought of. My 99 xj has a overhead console computer that has a real time mpg mode and a running average. This will come in handy for my future mpg experiments that were requested by popular demand.

Anyway, driving habits are the first thing I talked about on this post. They truly have the most effect on mpg. I drive the speed limit or slightly less than the speed limit, and I accelerate as smoothly as possible. I also let up on the gas pedal when my rpms reach 2000 so the tranny will shift to a higher gear. With stock gears and slightly larger than stock tires, I can accelerate to 65 mph without the rpms going over 2000 rpms at any point. It takes longer but the rewards are there.

Fans are not created equal. Diameter is only one parameter. Number of blades and the blade pitch are all important factors in how much air a fan moves. So the belt fan you replaced on your car was bigger diameter than the Jeeps belt fan, but the blade pitch and number of blades are almost certainly to be different. Those can lead to false impressions. Bigger doesn't always mean more. The diameter of the pulley also has a huge effect on fan speed. The Jeep pulley diameter and the cars diameter are almost certainly different.

Look at props on boats. Even if two props are the same diameter they could be designed for different purposes, (waterskiing, vs. trolling). And those design differences come from the blade pitch.

 

[j99xj]

This will come in handy for my future mpg experiments that were requested by popular demand. [\quote]

I'm changing my mind about running the before and after tests. I really don't think its needed.

Dr. Dyno got 1.4 mpg http://www.angelfire.com/my/fan/electric.html
GoJeep got a 5% increase with amounts to about 1 mpg. http://www.go.jeep-xj.info/HowtoElectricFan.htm

These folks are the most credible Jeep maniacs on the internet. The average of the numbers is 1.2 mpg.

This is lower than my 1.5 mpg figure. But it is not a bad estimate.

This guy got about 2 mpg on his f150. http://www.obd-codes.com/howto/electricfan.php

 

[Big Red]

I know results are greatly influenced by your driving style, but I have a 98' 2 dr, 5 speed, 231 XJ and a 96' ZJ fully loaded limited with a V8 and NP249 AWD. I know that the ZJ is a gas hog averaging about 13-14 MPG with street and hwy driving to work 15 miles each way. The 98' XJ is sitting and I have it listed for sale, but I'm thinking strongly of using it as my commuter dd. I already have my 91' 2 dr wheeler, and like 2 dr XJs.

What kind of gas mileage are you guys getting on a stock 5 speed XJ typically? Does 18-22 MPG seem reasonable? Do manuals do better with their 3.07 gears compared to the autos with their 3.54 gears? I drove the XJ cross country from Northern IL to Sacramento, CA and I didn't keep track of the mileage, but I thought I did pretty good about 20 MPG or so, maybe more. I know the XJ is quite a bit lighter than my 96' ZJ Limited, how much I don't know, but I think it's 700 lbs or so, maybe more.

If I keep the ZJ, I'm probably going to take off the front driveshaft, now on 93-95' ZJ with NP249 this will damage the VC, but on 96'+ the NP249 saw a improvement and it shouldn't hurt it from what I read on the ZJ site NAGCA.com, what do you guys think? Can I see about 2 MPG increase if I take off the front driveshaft so I don't have AWD? I don't need it here in Sacramento, especially not in the dry summer.

Troy

 

[streetpirate]

I'm able to get 19.8mpg with city/highway mix 3.55's and 26.4in tire.
and it gets it to the floor every day.

right now i cruise at 2250 at 70,

would the mileage have a huge change if i regeared to run 2700ish at 70?

 

[Big Red]

I'm able to get 19.8mpg with city/highway mix 3.55's and 26.4in tire.
and it gets it to the floor every day.

right now i cruise at 2250 at 70,

would the mileage have a huge change if i regeared to run 2700ish at 70?

I don't know how huge, but 2700 RPMs is getting up there. I try to shoot to staying under 2500 in my final gear. I can do this with my 91' XJ 4.0L/AW4 on HP44/9" and 37's with 5.43 gears in the 9" doing 70.

I'm still learning my 5 speed 98' XJ 4.0L 3.07 geared dd XJ. I'm doing 90 at about 2600-2750 RPMs or something like that. I'm going from 215 tires to 30" BFG Long Terrains, but I still hope to get at least 15 MPG city/hwy & 19 or so strictly hwy, I'd be happy with this over 13 MPG if I was lucky city/hwy with my V8 AWD 96' ZJ I just sold.

Troy

 

[j99xj]

I think I figured out why the mpg of people on this forum are so polarized. I think its because the people that have upgraded tires sizes have not changed the speedo gear in the transfer case.

In other words, when the odometer reads 1 mile more than before, the people with bigger tires have actualy traveled more than that distance. This will seem to lower the mileage for those people.

About a year ago when I bought my new tires I went about an inch higher than stock. Now that is not a huge difference, but since I travel at relatively high speeds on the interstate (75 mph) I wanted the speedo to be as accurate as possible, so I got a different speedo gear. I found a chart that has a list of tire sizes and the correct speedo gear for that size. I don't know exactly where that chart is but I'm sure its around somewhere on this www.

 

[jeepdude10000]

distance per time driving also changes MPG. I got a new job, within 3 miles from home, My last job was 12 miles from home, I use to get 23 MPG to and from work and now I get only 16 MPG.

Oh yea I get to play with a big 4X4 now on the new job she only hits 26 mph but she has grunt.

 

[Dr. Dyno]

I'm changing my mind about running the before and after tests. I really don't think its needed.

Dr. Dyno got 1.4 mpg http://www.angelfire.com/my/fan/electric.html

The mpg gains occur mainly during stop/go city driving where an electric fan is needed most and a clutch fan would be working hardest. On the highway where you have enough ram air cooling of the radiator, you don't need a fan and the clutch fan is virtually inactive anyway so mpg gains would be minimal.