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Old 11-20-2007, 08:03 AM   #1
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I have an SUV!

I move around the country quite a bit and need the storage and 4x4 capabilities of a large vehicle. My 1998 isuzu trooper has 230000 miles and still going strong, but filling it up with premium fuel slays me at $75-80+ per fill up.

Anyway, I get an average of 15 mpg at elevations below 7000 feet and an average of 23 mpg above 10000 feet.

I am really interested in making this vehicle as efficient as possible, even if that's not what it was built for. I'll be fueling up today, my commute is 24 miles daily on a snowy dirt road in rural Vermont, and this tankful I have gotten about 13 mpg.

So far, I have folded in the mirrors, toss it in neutral on all the downhills where it's safe (turning off the engine entirely while rolling causes a severe grinding sound followed by a large thump...probably not good) and keep the rpms between 1500 and 1900.

I plan on putting plastic sheeting over much of the front to help facilitate airflow around the many contours of the grille/fog lights and skid plates.

Some specs: Manual Trans, 3.5 V6, premium fuel.

Any suggestions on how I can improve mileage? My goal is 25mpg...maybe not "hypermiling" but enough to lighten the financial burden of driving such a beast.

Dan
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Old 11-20-2007, 09:13 AM   #2
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Since you have a manual...you can just coast in neutral where safe.

The biggest thing would be to air up your tires to ~50#s.

Take out any extra weight you don't HAVE to carry.

Keeping you highway speeds under or at 62.5mph/100km will do wonders for a boxy SUV.

I have an SUV also...diesel tho...25mpg might be a bit high to shoot for with a gasser...17-18 might be doable. 14 city/18 highway are the revised EPA estimates.

Why do you think you can't use "Regular"? Are you getting some "pinging" or 'detonation"? I know that Isuzu's, Rodeos included, do sometimes run better on the "midgrade"///but premium is just a waste on a lower compression engine like the 3.5L. In fact, premium can sometimes burn less efficiently and cause a loss in mpg.
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Old 11-20-2007, 11:45 AM   #3
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A couple of other things to remember:

Keeping a vehicle as long as you have actually helps the environment. It takes resources to build/transport a new vehicle and energy to demolish/dispose of an older vehicle even with recycling.

Also, since you have a vehicle that is already paid for and serves a real purpose...you are ahead of the game or at least on level ground. Just do what you can do and try to combine trips ect.
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2006 Jeep Liberty CRD...Founder of L.O.S.T.
OME 2.25" Lift w/ Toyo Open Country HTs 235/75/16s
ASFIR Alum Eng/Tranny/Transfercase/Fuel Skids
2002 Air Box Mod...Air Tabs (5) on Roof...(3)each behind rear windows
Partial Grill Block with Custom Air Scoop and 3" Open Catback Exhaust
Lambretta UNO150cc 4 Stroke Scooter



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Old 11-20-2007, 12:43 PM   #4
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Quote:
I am really interested in making this vehicle as efficient as possible
Don't focus most of your attention on the vehicle -- look at the driver, that's where a lot of problems and a lot of gains come from

However, 15mpg to 25 mpg is a 66% improvement - which is not reasonable given your scenario... That's hypermiling to the highest degree Extraordinary benefits require extraordinary changes. (For comparison, if I asked the same for my car - I'd go from 33 to 55 -- it's much easier to see how difficult that is given the same gains ).

--------
Frankly, it sounds like you're doing most of the beneficial items... Check out the driving list FAQ

-----
I agree about the comments on premium... Unless it specifically says "use premium" - don't. UNLESS you're occasionally using higher grade fuels for their cleaning packages (even then... meh).
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Old 11-20-2007, 05:35 PM   #5
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ScanGauge!!! You're vehicle has an ODBII port for you to exploit!
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Old 11-20-2007, 05:40 PM   #6
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Darby, I try and go about 52 - 55 on freeways and it's in a fairly smooth shaped crossover... speed kills mileage according to my ScanGauge. I think for me 40 mph is about optimum but the mpg drops slowly until after 50 mph (maybe from 30 to 28 mpg when it actually is flat). It drops off quicker under 35 mph because the torque converter unlocks.
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Old 11-20-2007, 05:47 PM   #7
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Engine Block Heater would probably be the best investment unless you have to have a dealer install it. It might easily cut the distance it takes you warm up in half and during that time you are using 2 to 5 times as much fuel.
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Old 11-22-2007, 06:55 AM   #8
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I use premium because it misfires with regular. Even 93 octane is sometimes not high enough, requiring the use of one of those octane boost additives.

Does removing the catalytic converter help mileage? The car is registered in AZ, one of the last states where that is a legal modification.

The vehicle has a deep cycle RV battery for cold starts, and if I could get a second one hooked up, I could completely remove the serpentine belt, thus saving quite a bit. The only draw back is I'd have to charge the batteries on a regular basis, every couple days or so.

I do take the back seats out when I'm staying in one location for a while. They weigh up to 150lbs, and this saves a bit.
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Old 11-22-2007, 10:12 AM   #9
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Quote:
Originally Posted by deathvalleydan View Post
I use premium because it misfires with regular. Even 93 octane is sometimes not high enough, requiring the use of one of those octane boost additives.
There's a simple solution for that.... Diagnose your problem (if you can't, bring it to someone who can) It could be something as simple as a tune up Going higher octane is just a band aid

Quote:
Originally Posted by deathvalleydan View Post
Does removing the catalytic converter help mileage? The car is registered in AZ, one of the last states where that is a legal modification.
At what human cost? In any case, I'm fairly certain emissions equipment is federal level law - not state. Weather or not your state checks is another story.

Quote:
Originally Posted by deathvalleydan View Post
The vehicle has a deep cycle RV battery for cold starts, and if I could get a second one hooked up, I could completely remove the serpentine belt, thus saving quite a bit. The only draw back is I'd have to charge the batteries on a regular basis, every couple days or so.
Extraordinary gains require some form of compromise Members have had great increases by removing their alternator. BUT, if you have a serpentine belt, it's probably driving something else you need. Check on that before doing it

Quote:
Originally Posted by deathvalleydan View Post
I do take the back seats out when I'm staying in one location for a while. They weigh up to 150lbs, and this saves a bit.
Should def. help if you're in a hilly area
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Old 11-27-2007, 05:39 AM   #10
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I joined just so I could reply to this thread.

My wife and I had the same Trooper you have. The most beneficial maintenance item that needs careful and timely attention is the EGR valve. It is located on the passenger side firewall and looks like a miniature R2-D2. We had to take this off every oil change and give it a good cleaning. I would usually soak it down with carb cleaner, and make sure the pintle inside moves freely.

If you are using high octane gas because your engine kinda burps then this is a major culprit. The plugs are easy to change and the NGK plugs made a big difference in MPG and all around driveability.

There are mnay helpful writeups here.

http://www.isuzufaq.com/
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