Improve your Montero Sport Gas Mileage ...
Disclaimer: The following text is documentation of the results of modifications on my 1997 Mitsubishi Montero Sport LS only. In no way is this document or any part thereof a guarantee of results. The reader should also be aware that any or all of the following modifications may void in part the manufacture's vehicle warranty. In addition, some or all of the modifications herein may not be legal in locations with Emissions testing.
That said, I want to make it clear that the following modifications have not affected my Sport in any way that has been detrimental. In fact, my Sport now passes Colorado Emissions test better than it did prior to the modifications. I am EXTREMELY happy with the following modifications. With 35x12.5x15 inch tires, 12+ of lift, Dana 44's, Garvin roof rack and 7" IPF overhead lights and several hundred pounds of additional add-ons and gear I STILL get between 17-20 MPG. Ha! Find me a Jeep that can do that! I should point out that before the IFS to Solid Axle Conversion I was getting a solid 19.75-21. Both of these are almost a 50/50 mix of city/highway driving. Please keep in mind this is city/highway driving on the front range - 5500 ft.+ - and mountains of Colorado. Obviously this changes if I go to lower altitude. Sound interesting? It gets better. After the first six months of minor modifications I was averaging 24-26 MPG - same mix of driving. "IMPOSSIBLE!", you say! No, actually, its not. Its not because there are some very simple modifications that can be made that effectively free up power in your vehicle that is currently being wasted by an incredibly inefficient design. I wont' go into the reason for the design - I argue theology on a different page.:-) On a side note, I should point out that my modifications have also done wonders in the power arena - low end torque and upper range HP have increased very noticeably!
Modification level ...
- Stock - 22-24 MPG
- Light - 24-26 MPG
- Moderate - 19.75-21 MPG
- Insane - 17-20 MPG
There is a very good reason for the huge jump in gas miliage with the change to synthetics. Due to the design of the Montero Sport all the front axle parts - i.e. wheel, half shafts, differential, drive shaft - turn whether the vehicle is in 4-High/4-Low or 2-High. Rotating all these parts requires a good deal of horsepower and torque. Fuel is required to generate that horsepower and torque. Unfortunately that fuel isn't being used to actually get you anywhere, its just going to turn these parts. If the amount of force needed to turn these parts is decreased - i.e. using synthetic oils - an increases in gas mileage will be seen because less gas is being burned. Bonus! The torque and horsepower that WAS being absorbed by the front drive train parts is NOW available to the rest of your vehicle! Noticeable increase in seat-of-the-pants-pickup and hill climbing.
The tires had to go! Its SO embarrassing getting stuck trying to drive out of a gravel driveway. Sigh. 31x10.5x15 BFG A/Ts were the trick addition. Gas mileage actually increased, as I said above, but seat-of-the-pants-pickup decreased as well as high speed performance at altitude - 10-12,000 ft.@60-70MPH. This was to be expected since the BFG's were something like 1" larger in diameter and wider yielding not only a larger contact patch, but taller effective gearing. So gain with the synthetics kinda canceled out the loss from the tires in seat-of-the-pants-pickup. I ended up with a net gain in gas mileage but no loss/no gain in performance.
April 2012: I recently purchased another 1997 Mitsubishi Montero Sport LS 3.0L 5-speed in stock form. This vehicle is an exact clone of my original Sport with 170K miles and no modifications. Before making any modifications myself I added the ARB Bull Bar and Warn XP9500 with the original steel winch cable. Prior to the modification the mileage was in the low 20s. Right about 21-22 MPG with a 50/50 town/highway mix. The addition of the Bull Bar and winch dropped the mileage almost exactly 2 MPG. I was able to run a good test of an almost bone stock vehicle against my highly modified original Sport (see the Insane section) in April 2012 by taking it to Moab for a week. Under the same operating conditions and following the same routes my new Sport averaged just a tad more than 1 MPG better than my original Montero Sport for the entire trip.
The bigest difference noticed was the distinct drop in 'get up and go' on the highway. In stop and go town driving there was almost no difference but on the highway it was very noticable - especially at highway speeds in the 75 to 80 MPH range. I'd suspected for quite a while the problem was the change in aerodynamics but had no way to really confirm my theory. Until now. Prior to adding the bumper and winch I loaded up the new Sport with the equivelent weight and then drove my usual routes. The extra weight was noticable (barely) but that was the only effect. My conclusion is that, like the roof rack and lights the bull bar significantly decreases aerodynamic efficiency.
So, my next modification was (desperately!) called for. Manual locking hubs. THIS was probably the best, most effective modification in terms of mileage and performance increase that I've ever made. This change brought back almost all of the power I'd lost with the increase in tire size and decrease in aerodynamics - somewhere on the order of about 85%! It was great!!! As previously mentioned above, the front axle assembly rotates all the time and using synthetics will help decrease the amount of force required to rotate these parts, but not eliminate the requirement. Manual Locking Hubs ELIMINATE the requirement by disconnecting the wheels from the axle shafts. Once the wheels are disconnected from the front drive assembly they are no longer forced to rotate all that mass that is your front drive train. An additional modification was also made which is not performance/mileage related, but is directly related to the hub replacement. A steering stabilizer. I HIGHLY recommend this to compensate for the "loose" feeling that comes with not turning several hundred pounds of metal in the drive train when the hubs are unlocked. Its not necessary but I like a tight steering, so.... Bonus! When you have the hubs unlocked you're not turning all the front drive train parts so therefore you are ALSO not subjecting them to wear and tear!
Two additional modifications were made not too shortly thereafter. A K&N FIPK air filter kit from a GT3000 was installed and replaced the stock air box assembly entirely - my original stock replacement K&N filter migrated to my friends '98 Sport - and a cat-back system was installed. The FIPK filter kit did wonders for highway performance but surprisingly it made MORE of a difference in the low end torque! Noticeable enough that passengers were asking if I'd done something to the vehicle! This bumped me a little closer to 20 MPG. Next the cat-back. This was actually necessitated by the act of my planting the original set up on a rather large and pointed rock! Ouch! FlowMaster muffler with a 2 1/2" custom built exhaust from the catalytic converter to the bumper. I've had only one problem with this and that was immediately after install. This exhaust worked SO WELL that the truck wouldn't RUN! I managed to limp the truck the mile and a half home where I disconnected the battery cables and let it sit for two days to completely discharge the vehicle's computer back up battery and reset the its computer. I am serious, "limp" is not quite strong enough. The vehicle wouldn't IDLE! Stumble, stutter, etc. Nasty! However, upon plugging the car battery back in and taking it for a short 5-6 mile drive everything was fine and has only continued to get better. Increasing the breathing ability of the engine that much threw the computer out of adjustment more then it could compensate for. Hence the need to reset it to its defaults and let it relearn about the new system. The exhaust, combined with the new air cleaner assembly, gave me a huge gain and put me back in the high 19-21 MPG range. A solid increase in torque in the bottom end and a very nice improvement in highway performance. Using it for what I do, however, I was most happy with the torque increase. At this point driving with the 33" tires, rack and gear was not very much different then it was under "Light" with the exception of the MPG on the highway, but off road performance was much better then it was with "Light".
I have to note here that almost of the modifications I've made to my Sport have extremely detrimental effects on highway performance. Wider tires, big tires, roof racks, bumpers, side bars, externally carried gear, etc. All of this adds weight, decreases aerodynamics or increases rolling resistance. None of this is good for performance or gas mileage and almost all of it has a progressively worse effect the faster you go. Unless engine modifications are made there is a limited amount of power available to push the vehicle.
March 2010: The stock Mitsubishi transfer case has been replaced with a Jeep NP231J transfer case with Tera Low231 and D&D Machine's NP231 doubler. The weight difference is negligible but the new assembly appears to be slightly more efficient as mileage increased slightly.
April 2012: Its interesting to note that this engine has 530K+ miles on it and a cylinder going south yet still gets 18+ in stop and go town driving and will easily break 20 MPG driving back and fort to Moab, UT over two 11,000+ foot passes.
Some of the modifications are very easy and some are a little more time consuming but I've been happy with all of them. I intend to try two more now that the conversion is finished and stable. I intend to have the computer reprogrammed and install a slightly larger throttle body. I'm hoping this'll get me back to 20 MPG. We'll see! At least it'll be fun to try!:-)
May 2012: I wanted to add a little addendum to this article. The original engine in my LS Sport, the same engine referenced in this article and now with more than 530,000 miles on it, finally decided it was through. While in for spark plugs and wires, we discovered that the compression in cylinder #3 was at less than 80 PSI while the rest were still at 150-160 PSI. Something to note: this engine still passed Colorado Emission testing BETTER than my other two stock Montero Sports - my 1997 3.0L LS and 2003 3.5L Limited - both with 1/3 of the mileage. Due to the extrodinary amount of mileage on the engine we decided it was time look at either a new engine or a rebuild. Applying 'band-aids' didn't seem like a good idea. So, the decision has been made to transplant a 2000 3.5L Sport engine into my 1997 3.0L Sport. It'll be interesting to see how that works out ...