Hypermiling an SUV: A Case Study (2007 Mitsubishi Endeavor AWD, 3.8L)
 

I’m writing this as a case study and not a vehicle review for 2 reasons: I’m sure you wouldn’t buy this vehicle for it’s FE, and secondly, there seems to be a few new guests to GasSavers that could benefit from the techniques and results utilized on this test.

The fact of the matter is, any vehicle can probably be hypermiled. If you’re coming to this site looking to improve the fuel economy of whatever you drive, then that’s OK. Some may argue that it’s not worth it, to trade in the vehicle, or forget about it. There’s another approach.

It’s not always feasible to immediately trade-in a guzzler, especially with the hard financial implications in the current large, used vehicle market. When it does come time to purchase a different vehicle, perhaps a smaller (or more fuel-efficient) one could be considered. Until then, here’s what I did to get the SUV to 43.5% over EPA.

The test vehicle is the 2007 Mitsubishi Endeavor. The engine is a high-compression, SOHC, 3.8-Litre, V-6. The drive-train is a full-time all-wheel drive system, with a 4-speed automatic and lock-up torque converter (with a “Manu-Matic” shift gate).

https://pic16.picturetrail.com/VOL698.../258530575.jpg
Photo by RH77

Why am I driving this? I wondered the same thing for the whole trip. We reserved a “Compact Car” – like a Kia Spectra, but they were all out of car-like vehicles. Our choices: Jeep Liberty, Jeep Grand Cherokee, or the Endeavor. A quick scan of the EPA database in my head said “take the Mitsubishi”. (It turns out that they all had almost identical EPA values – I drove the Liberty before and really disliked the lack of foot room, so in retrospect, I probably should’ve taken the Grand, as you’ll see later).

The test location: Yellowstone National Park and surrounding areas, including Bozeman, Montana, West Yellowstone, portions of Idaho and much of the Park in Wyoming. Driving style: Lots of stops and starts on scenic drives (park limit = 45, much was 35). Highway speed limits outside the park were 75mph (MT recently had to restore their speed limits after the obvious was happening).

https://pic16.picturetrail.com/VOL698.../258530574.jpg
Photo by RH77

EPA Averages: 15-City, 20-Highway, 17-Combined.

Here’s what I did and why (from easiest to hardest):

1. The first “modification” was to over-inflate the tires. Despite driving on gravel roads, off to the side of roads with large rocks, and over rough, off-road terrain, no punctures developed and the tires were fine. Less rolling resistance = better FE.

2. The weather was warm, but with the windows at full-down at 45 or under, and partial at 45+ yielded less accessory drain, and a comfortable environment. Less Accessory Load = Better FE.

3. As you can see, it’s a big, bulky vehicle, that could use some aero treatments, so one item was to keep the speed under 65 (55-60 seemed to be the best when nobody was following or on the Interstate). This was only applied on the highway to-and-from the park with 75 being the norm. 65 seemed to keep folks content on the 2-lanes. Less Aerodynamic Drag = Better FE

4. Reduce idle time. An idling vehicle gets Zero MPG. Not using fuel needlessly = Better Average FE

Side Story #1: “Uh-oh”

…and the darn thing wouldn’t start – twice. After pulling to the roadside to look at some wildlife, I went to start it. It would crank and crank but nothing. I popped the hood like I knew what I was doing, and had my wife turn it over. Nothing out of the ordinary. I ensured wires were connected, retried it, and nothing. After 5-10 minutes of wondering what to do (no cell-phone signal) – it finally started. When we got a cell signal, I phoned the rental agency, who promptly declared it “Vapor Lock” or an air bubble in the fuel (I wasn’t really buying it, but it wasn’t throwing any codes, so who knows?). If it happened again, we were to return it to the other agency where we were staying, but it apparently was “an anomaly”. It did it again: but not for another day or so. This time it happened on restart during EOC – had to coast to the side of the road and wait, again…too late to return it.

5. One of the first things to do with any vehicle is to get to know the vehicle. Monitoring the ScanGauge showed how the engine operated, and at what speeds. Since it was equipped with a gear-holding, automatic transmission selector, you could “slap shift” it into a higher gear when the computer detected that it was safe to do so – same with downshifting. The engine exhibited an odd behavior which I figured-out later. At higher loads with low RPM, timing fell as did FE. Keeping the engine at 2000-2500 RPM yielded the best FE under load (3rd Gear generally). Under light loads such as level ground or on a slight downhill, top gear and a light throttle was used. Knowing what the engine wants can = better FE

Side Story #2: “Can of Marbles”

I found out a few days later why the timing was being retarded on such high loads. Going up hills the engine knocked like crazy. It turns out that it required premium fuel for the high compression, and was reducing the timing to prevent (so much) detonation. At these elevations, the “cheap fuel” was 85.5 Octane. When we would descend down to lower areas, the engine just had a tough time with, well, the timing. Perhaps it reduced fuel consumption – not sure, but for longevity, the rest of the test used 88 (or mid-grade – still knocked).

6. The above techniques yielded about a 3 MPG, or 17.6% increase. The final tank reading was 24.4 MPG or a 43.5% increase over combined EPA. Bear in mind also, this was in high-altitudes – which had an advantage: EOC. The biggest increase in FE was engine-off coasting on the long dowhills of the Park. The SG average speed was 32, which seems also to be ideal. With a large, AWD vehicle, special care has to be taken to ensure that braking will be sufficient with your vacuum reserve and that the power steering will be VERY heavy – but if attention was paid, a hard stop could be achieved (tested well, when we saw a Wolf close to the road – I stomped on the brakes and the vehicle stopped as normal – first brake actuation after EO. Remember: more pumps = less vacuum lost = harder to engage the brakes).

At every opportunity, EOC was used to coast at 45 mph or slower, down grades – with “every opportunity” translating to a sufficient coast distance. Coasting with the engine off = an infitite MPG figure

In conclusion, you can probably hypermile anything out there. While 24 mpg is paltry compared to an economy car, compared to the standard “just drive it style”, the effort yielded significantly better emissions, FE, and hit to the wallet.

Raw Data:
Model: 2007 Mitsubishi Endeavor
Class Size: Large, Specialty-Purpose 4WD (SUV)
Trim: LS
Transmission: 4-Speed Automatic with LUTC
Engine: SOHC, 24-valve, 3.8L, V-6 (cast iron block): rated at 225 HP and 255 ft-lbs of torque
Drivetrain: AWD
Gross Weight: 5250 lb.
EPA (Old Estimate Calcs): 17/21/19
EPA (Newly Estimated Calcs): 15/20/17
GasSavers Tested Mileage: 24.4 MPG (ScanGauge Verified)
Fuel Consumed: 17.7 gallons
Speed Avg: 32 MPH
Time of Operation: 13.5 hours
Distance Driven: 432 Miles
Ambient Outside Temp: 50-85F

RH77

Maybe you should enter that in the Team Challenge:) . Sounds like a nice trip and nice job on the FE.

Nice write up but, don't tell me you put 85.5 octane in the tank of the vehicle. You should never use anything under 87 unless its a lawn mower or small engine like that.

yes. lawn mowing is VERY popular there, so they stock a grade of gas that is ONLY suitable for lawn mowers.

sigh.

lol as long as it doesnt knock your fine.

Here's the problem
 

Basically, here's the problem. The vehicle is filled by the previous renter, which probably included a full tank of the cheap stuff. So, I set-out on the trip with a tank of weak fuel.

After the first tank, I put the 88-octane in it, hoping it would increase FE, reduce the liklihood of the failure to start, and the driveability issues.

Folks who live in mountainous areas can probably help here, but I think the lower octane is to reduce emissions at higher elevations (and may decrease the minimum-number requirement for engines that operate in that atmospheric condition).

It was very common throughout that region to see 85.5, 88, and (90?) as the fuels available. Since it was so remote, the prices were at least $3.30 in most areas, up to $3.70 for the cheap grade. I think people put it in their cars, even though most Owners' manuals state minimum requirements regardless.

RH77

Ya, octane requirements are lower at altitude.

Thanks for this. I drive a Mazda Tribute, and it's not feasible to trade it in right now. Besides, it's paid off! I have increased my mileage from 19 mpg to a best of 25 mpg.

My job situation will change within the next year, and I'll be able to get a car that is much easier to hypermile.

m

Indeed. Most of that area is in the 3000-5000ft range for elevation so there is significantly lower atmospheric pressure and the higher octane is not needed.

You're Very Welcome
 

M, Folks like you are the reason I started this thread. Just because someone has a truck, van, or SUV doesn't mean that you can't decrease fuel consumption.

If people visit here and make the commitment as you have, then it's very likely improvement will occur, in just about anything.

The important thing for folks to remember in this case, is to select the smallest vehicle that will suit your needs. M is a good example, as he's decided to consider a more fuel-efficient vehicle for the next purchase.

I'm a big believer in renting trucks when you need them. I understand that in many cases this isn't feasible for some, but during the 1 time a year that I need a vehicle with 4-Low, I just rent one. The money saved by driving a small car (in my case) is considerable vs. having a large vehicle for rare occasions.

Thanks again for the feedback :)

RH77