There are a ton of fuel economy threads, I know. I figure one more isn't going to be a huge deal. However, this thread is a bit different. I'm not asking, but providing my findings after driving over 1800 miles in 5 days. Most fuel economy discussion center around highway miles, so that is the focus of this thread.
I'm doing this, hopefully to answer some questions for a lot of the people who ask how they can improve their fuel economy. I'm concerned about fuel economy just like most people, especially with fuel costs that don't seem to be going down at all. But I'm also interested in having fun off road. I'm relatively new to the off-road scene, but am no stranger to modifying vehicles. Just rounding out my hobby skills a bit more.
Before I get into the results of my fuel economy, you guys need to know where I'm starting from. Here's the specifics to my WJ:
2004 WJ Laredo, currently with 109,xxx miles and with few options. I bought it to be modified for off-road use, so the less gadgets, the better. Has A/C, Cruise, power doors and power locks and that's about it. I did not purchase this new, but rather with 77k miles on it a couple years ago. I have no idea what the PO did for maintenance.
4.0 Inline Six
OME HD Springs
OME 10mm Spacers
Bilstein Shocks - 5100
JK Moab 17" Wheels with 255/75/17 Good Year Wrangler SRA tires at 35 PSI
SCT Flashpaq with Mileage XS tune installed
(Total lift including because of tires, approximately 4.75")
New paper filter on stock intake
Oil changes use BG MOA at every change (3k miles)
BG 44K every ~10k miles
Transmission serviced roughly 25k miles ago
Transfer Case serviced roughly 25k miles ago
(No fluid change yet on the differentials)
Now that that's settled, I think my WJ is not unlike a lot out there. There are no long arms, but it has been lifted on as large of a budget that I could afford with 4 kids at this time.
I took my oldest to Laramie, WY from Lincoln, NE for his college freshman orientation last Wednesday, so I figured it would be a good time to conduct this small experiement since I had all the pieces put together.
We started at an elevation of approximately 1200 feet and ultimately climbed to an elevation of over 10,870 feet. Most of my time was spent at an elevation between 7200 and 8300. I made a few detours both on the way there and the way back that basically doubled my miles if I had just taken the interstate the whole way.
As far as fuel economy goes, speed has a huge impact. The wind resistance increases force exponentially as you drive faster. For the purposes of this experiment, I kept my maximum speed to 65 mph. I did have about 30 miles that I bumped it up to 70 on the way home, but backed it back down because I could see the mileage was dropping quickly (via evic...I know it's not accurate, but it is an indicator.) Not only did I have plenty of hills that I drove, but I also took advantage of my time in WY and spent about 4.5 hours in the back country 4-wheeling. About 30 minutes of that time was before we got out there exploring the sandy beaches of Lake McConaughy in Nebraska, the other 4 hours were off road in WY. Also, just today, drove about 20 miles on muddy gravel roads that required the use of 4-wheel drive most of the way. Needless to say, I did spend some time wheeling it and those results are included in my findings.
All mileage calculations were done with the aid of a GPS. It chronicled that I drove a total of 1822.7 miles while using 84.864 gallons of gas. I started with a completely full tank and just filled it up again tonight to keep the accuracy correct. That yields a mileage of 21.48 miles per gallon. The best mileage I got on a tank of gas was 22.5 while the worst was 18.9 (that was my off-road time). I kept the Mileage XS tune on the WJ the whole time, but did make adjustments for my tire size based on miles driven.
It should also be noted, that I was not driving an empty Jeep. Besides myself and my oldest son, I also brought my 10-year old daughter. We spend a couple nights camping east of Laramie. So not only did it have 3 passengers and clothing, but also camping gear and food. I could only see out of the very top of my rear window and the 60 part of the 40/60 back seat was folded down for gear. Needless to say, it is how many will probably drive their Jeeps to wheel.
I will also mention that if you are concerned about fuel economy, keep off the go-fast pedal. This is most important in accelerating. These aren't drag-strip Jeeps, so don't drive them that way. I didn't. Probably killed my 18 year old son, but consistency was part of my experiment. And the farther you can anticipate a slow-down or stop, anticipate it. Finally, use the cruise control. The computer is much better about maintaining speed by using the least amount of fuel than your foot is.
Tires also affect the fuel economy greatly. The more aggressive the tread pattern, the lower your fuel economy will be. If fuel economy is that important, consider investing in a second set of rims for your aggressive tires. I have the rims, just not the tires yet.
Now for the evic: Yes, it is not accurate, but it is only as smart as the input. I spent the money on the flashpaq not really to save fuel, but for the ability to change my tire size. I found a couple things. First off, my tires measure 32" tall. I put that in the tuner initially and was quite a bit off both on the speedometer and the odometer. It took some adjusting over this trip, but I ended up adjusting the tire size through the flashpaq to 31.5 inches. This brought my speedometer to within about 1 mph and my odometer now reads about 0.18% over actual mileage. I don't believe I can make any finer of adjustment than that considering I am limited to adjusting the tire size by .25" increments. After getting that adjustment made, my evic is almost dead on. In two separate legs of my journey after final adjustments, my evic read that I got 22.5 and my actual was 22.5. Today, my evic read 21.5 and my actual was 21.86. They are not supposed to be 100%, but to give an indication as to the fuel economy. I think that given the adjustments, my evic is as accurate as it can be. By making sure that my odometer and speedometer were accurate via tuning, the evic became accurate as a side-effect. I will continue to monitor and it may make a liar out of me in the future, but that was the accuracy after driving over 1000 miles in the last couple days.
At any rate, those are my findings and words of wisdom for those hoping for better fuel economy. I'm sure some will flame me, but I know not everyone will. I believe I can further increase fuel economy, albeit, not greatly. I might be able to sqeak out 23.0 every now and again wtih a few more modifications. I'll look at doing those in the future and reporting back. Don't have the money for them right now though since I just installed my lift a week ago.
And just for your viewing pleasure, below is a picture I took while I was out in the back country in southeast WY.
Thanks for the reminder... I forgot to mention that I use the highest octane fuel available that does not contain ethanol. It is getting more difficult as the government mandates more and more ethanol blends. Even the 10% ethanol has a measurable effect on fuel economy. I kept extensive records for a year of significant travel (2k mile trips every 3 weeks) and confirmed several fuel saving tips. One was non-ethanol fuel. I found almost a 10% decrease in fuel economy when I used ethanol.
I have not experimented with octane ratings yet with my 4.0 though. Although one fill up I could only get 88 octane instead of 91. I'm not sure of other factors influencing the results, but for that leg of my trip I averaged 21.4 mpg. It could have been due to the lower octane/ethanol blend. I was traveling on a relatively flat road (I-80) going from 2400 feet to 1200 feet. But there were too many other variables that could have been affecting the fuel economy. But after filling up with non-ethanol 91, I then got 22.2 mpg over a greater distance and constant hills.
Ethanol is a nightmare and I wish it was not in gas!
Running more than 87 in the 4.0 isn't going help at all from what I've been told. Shoot, I have even been told that running higher octane such as 93, will result in worse economy. I've stuck with 87 and the 87 Tune on the SuperChips
Another very valid point you made previously was speed vs. MPG. I can cruise at 60 and look at 22-23 MPG all day long. But, running 80+ MPH I am looking at 17-18 MPG.
~ 04 WJ 4.0 | Selec-Trac 242 | MBP | OME HD 3" Lift | JKS TB | IRO Front LCA's and UCA's| Bilstein 5100's | Custom Front D.S. | Stillen Rotors/Metal Matrix Pads | Tow Package w/ 3.73's | Projectors w/ 55w HID H1 5000K Lows | Sylvania Ultra 9005 Fogs | Moog HD Steering | Kenwood eXcelon Radio | Memphis Speakers | Alpine Amps | Alpine Subs | Moog STB SS | Superchips Flashpaq | Auxiliary Transmission Cooler | Rock Lights | Light Bars ~
Agreed, Ethanol is garbage and when E15 starts showing up at stations dont use it!
I always run 87 in the 4.0 (Its compression ratio is almost diesel like) and run midgrade or higher only when towing since the 4.0 doesnt use any knock sensors so the computer cant pull timing to retard it.
Crusing at 65 I normally see 20-21 (I have 3.73 gears) and anything much above 70 makes it drop to the 17-18 range.
Bear - 1999 Jeep Grand Cherokee Laredo - 250,000 Miles, BDS 2" lift, Overland rock rails, Dynomax cat back exhaust, 245/75/16 Kumho KL78's, Rebuilt 4.0 @ 244,000 miles.
Apollo - 2008 Mazdaspeed3 - Mazdaspeed CAI, Mazdaspeed CBE, Prosport boost gauge.
Velvet - 2005 Ford Focus ST - Wife's ride
Gasoline engines, no matter what they are do not run anything like diesel compression. If the 4.0 were closer, say 11:1 (still not diesel compression ratios) there would be much more tuning requirements as well as decreased durability. And we'd be required to run 91+ octane at all times. Diesel compression would likely still detonate running 110 octane racing fuel.
The compression of the 4.0 is an anemic 8.8:1. Increasing the compression ratio to about a 9.5 would still allow for forced induction and make tremendous power/torque numbers. However, that will require specialty parts and I have yet to look I to that possibility... Already have a for Ed induction car...
For comparison purposes, diesels run compression ratios that range from 15:1 to over 20:1. Many performance gas engines run a max of about 11:1 and alcohol engines run a bit higher.
Here I've been playing with using 87 and 91(which contains no ethanol) both from shell. Running 91 gives noticeably better gas mileage. Depending where I buy though will cost me 11-18cents more /litre.
The beatings will continue until attitudes improve!
I conducted experiments with octane in my GM 3.8 n/a and I was surprised that the higher octane 91/93 (depending on location) got better mileage to the tune of approximately 2 mpg. But that was when I drove 2000 miles every 3 weeks for a year. Kind of kept that same drive a little different every trip. LOL!
Based on those results, any time I'm driving distance, I use the highest octane possible. Maybe if I drive my Jeep on more long trips, I will experiment a little more with that. But for this experiment, I wanted to limit the variables as much as possible and the one tank of 88 octane might have affected the experiment. But at 12:00 am it was the 2nd place I stopped and wasn't willing to drive all over this town looking for better fuel... And that was after I'd been driving since 8:00 am and still had almost 4 hours to drive...
I will be looking in the future into more custom tuning capability which will give a lot more flexibility than the flashpaq. I will be able to tune to a specific octane (more aggressively than the flashpaq) which can yield more power with better fuel economy. It's like that with intake and exhaust. They both require custom tuning to take full advantage of the improved flow. That is why a lot of people don't see any improvements when they "bolt on" and intake and/or exhaust. Proper tuning can then take advantage of the capability.
Coming from a car community where the simplest of bolt one required custom tuning to get the most out of them, it surprises me that there isn't more tuning support for Jeeps in general.