Hello all, I decided I would try to cover a lot of fuel saving tips and tricks, as well as efficiency improvements everyone can do on their Jeep. I've made it a personal goal of mine to make my old ZJ operate in the most efficient way possible to save gas & achieve peak performance. Feel free to add your own tips, and I might add them to the main post!
And of course, keep in mind, this is a Jeep, not a Prius! You will never, ever see more than 20~MPG even in the best circumstances. This is just a good guide for those who want to squeeze as much as they can out of their Jeep
1. Clean up your fuel:
Because of the 1970's fuel crisis and awful low-quality gas getting sold, the government mandated a minimum amount of detergents to be present in gasoline in order for it to be sold. However, this minimum amount is just that-minimum. And if we've learned anything about the government...their minimum is probably not the best minimum to go by. Over time from using this minimum-quality gasoline, gunk & varnish will build up in your combustion chamber, gas tank, gas lines, fuel injectors, and basically all through your fuel system. This is probably the worst parasite of fuel mileage, at its worst before I got my jeep, my dad would get at most 15MPG on the highway and sometimes 9MPG in the city.
The first thing I did was get TWO bottles of Techron fuel cleaner (20oz, for 20 gal tanks). At 3/4 tank remaining, pour both bottles in your tank. At this higher concentration your fuel system will be well-cleaned.
After you have used this tank of fuel with Techron, and filled back up, at 3/4 tank buy 1 bottle of SeaFoam 16oz. Follow the recommended directions (induce through brake line, let sit for 10 minutes, start and let smoke. You may have a LOT of smoke, or just a little.), use 1/2 the bottle through the brake vacuum line, the other half dump in your fuel tank. This will clean up even more.
After doing both of these, at my 2nd fill up after I measured my fuel mileage. I was getting 12-13mpg city, 17-18mpg highway, an increase of 3-4mpg overall!
2: Keep your fuel clean:
Now that you have banished the gunk and cleaned your engine, to ensure you don't have all that hard work get tarnished by bad gas.
My uncle was a chemist for Texaco, and is now a top manager at Shell. He was the first to tell us to spend the extra 2-5 cents per gallon to get name brand gas, because the detergents in grocery store/generic gasoline, while meeting government standards, are not good enough for modern engines. He always recommended using name brand gasoline.
Therefore do NOT purchase gasoline from:
-Grocery stores, like Kroger, Stop & Shop, Market Street, etc.
-"Discount" stations, like Conoco, Phillips 66, Shamrock, etc.
-No-name service stations, with no branding or company affiliation
-In some cases, any rural stations, even name brand ones. They have been known to use crappy gas despite their corporate branding since they are the only gas around (and they charge far higher for it). Avoid them if possible.
Do purchase gasoline from:
-Name brands, like Shell, Chevron-Texaco, Exxon, etc.
You even get better fuel economy & performance from using good gas. You can always tell if you have gotten good or bad gas. I got gas at a rural Exxon station (a mistake), thinking it was good gasoline, before a trip home to my parents. Normally I get at least 18mpg on the highway, and on inclines on cruise control, my jeep never has to downshift to maintain speed. This trip, my jeep struggled up easy inclines, and I got 16mpg.
The extra few cents do make a difference, and often there are ways to get rewards for being a frequent customer at these stations.
Also, it is a MYTH that using Premium 91/93 octane gasoline will clean your engine better. Regular 87 octane (or the regular octane at your altitude) is still packed with detergents with the name brands, and is fine for ZJ engines (except the 5.9, which requires a higher octane. Always use the minimum octane recommended for your engine to prevent knocking).
3. Treat it like a baby
Over two years I have noticed when I drive a certain way, my mileage is affected. I've taken notice of RPMs, speeds, and the way I drive to form a conclusion on how to drive my Jeep for peak efficiency while maintaining reasonable speed/acceleration.
Findings for my Jeep (4.0, probably different for the 5.2/5.9)
-O/D can be achieved at minimum of 47MPH with small pulse of gas pedal.
-Best acceleration RPM is between 1750-2000 (between notch before 2 and 2)
-Best highway travel speed is 70MPH @ ~2050RPM
-Max highway travel speed (before large RPM increases needed) is 75MPH @ ~2250RPM
The best speeds are not necessarily the absolute most efficient, but they offer the best balance between reasonable speed & economy to keep up with traffic.
-Maintain a speed that offers minimum resistance. Too slow, and you will feel pressure and tailgating from other drivers, making yourself a traffic hazard. Too fast, and you will find yourself often having to brake or slow down when your path is blocked, greatly diminishing your fuel economy. Find a speed where you minimally have to slow down for slower drivers, without being a hazard for faster drivers. Often, this speed is the actual speed limit, or about 5mph faster.
-Coast when you can. If the light turns yellow and there is no way you will make it, just let off the gas completely. Whenever you use your brakes, you waste energy lost to friction from braking. The more you coast, and the less you use your brakes, the more energy you save.
-Drafting can be used to a point behind trucks. DO NOT DRAFT UNSAFELY BEHIND A TRUCK! Even 10 car-lengths behind a truck offers some drafting benefits. Pay attention and stay focused while driving, do not tailgate a truck.
-Travel at non-busy hours. While not an option for some, if you can drive when there are less people on the road, your fuel economy will benefit because you will have to slow down/speed up less frequently.
As always, stay safe while driving! DO NOT TOUCH OR LOOK AT
your cell phone/ipod/radio/anything while driving, except at traffic stops at most. DO NOT pay attention to anything but the road when driving, especially in heavy traffic. Be courteous, vigilant, and responsible on the road, and you can prevent accidents.
4. Keep it stock
I'll probably get some frowns when I tell people this, but if your absolute goal is maximum fuel efficiency, you can't get big tires and lifts. Lifts alter the aerodynamics of your vehicle, and cause drag that lowers your fuel economy as you lift higher. Larger tires & wheels put more strain on your engine to turn a larger diameter, reducing economy further. Winches, roof racks, bumpers, lights, anything that adds a surface for drag or weight will reduce economy obviously. Also changing your differential gear ratio will lower fuel economy.
One less obvious note I have to make, is that smaller tires REDUCE fuel economy. I had 225/70R-15 tires from my dad for the longest time. I figured out that I had to multiply my odometer reading by .93 to find my actual mileage, and calculate my actual fuel economy. After I got new 235/75R-15, which are much closer to my stock wheel diameter, I expected to either stay the same with fuel mileage. To my surprise, my fuel economy INCREASED by 1-2MPG with proper tires! So if you are trying to save $50 in tires, you will pay for it in gas mileage over the next 3-5 years you have those tires.
So in conclusion, stock fuel, oil weight, tires, height, etc are your best bets when it comes to fuel economy and efficiency. If you want a 7' lift and 40" wheels, that sounds freakin awesome! You just aren't going to get good fuel economy
5. Upgrade away
After doing the best you can with a stock jeep, it's time to look into upgrading things to get more power & efficiency. If you want to start down this road, plan to buy everything, because just one or even two upgrades by themselves will not make a difference.
Think: easy in, easy out. The easier it is for your engine to suck air in, the more it will be necessarily to make an easy route for it to be blown out! Now the 4.0 can only take in so much air, so a serious hardcore exhaust set it not necessary. Here is the set-up I would recommend:
-Altered stock airbox w/white restriction removed and front snorkel removed
-WJ-style "99+" intake manifold upgrade(my howto here
-Fuel injector "703 swap" upgrade(my howto here
-63mm bored throttle body (haven't done this yet, watching one sold on eBay
-Upgraded exhaust header(haven't done this yet, various ones recommended here)
-Magnaflow Hi-Flow Catalytic Converter(available from Kolak)
-Glasspack muffler(or any desired high-flow muffler)
That will be just about the best you can do without starting to do some serious engine/drivetrain work. Some other things to think of:
-Loading down your Jeep or trying to lighten it up as much as possible doesn't do much. Moving from Houston to Dallas, I hauled around 700-1000lbs of stuff at highway speed...and I don't think my mileage changed a bit.
-When idling, you get 0mpg. As a general rule of thumb, if you think you will be stopped more than 1 minute, go ahead and shut off your engine. Going inside instead of going through the drive through can save lots of gas (and, having experience working in fast food, if the drive through has more than 2 or 3 cars usually ordering inside will be much faster.)
And that's it. The above is the best possible scenario to achieve the best you can possibly get out of your Jeep. I average about 13-14 city and 18-19 highway mpg. Not all Jeeps are created equal, you could get more or less. But the above will get you the best possible efficiency.
So let this be the final answer for all the threads asking "how do i get better mpg?"