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Old 07-09-2008, 11:52 AM   #1 (permalink)
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'93 Jeep Cherokee - Weekend report

This past holiday weekend I did some tweaking to try to improve my fuel economy on the road. Given I drive a '93 Jeep Cherokee with 15 mpg combined, I appreciate any increase in efficiency. Here is what I did and its effects:

- I checked the tire pressures all around, and found my tires to be between 32 to 37 psi. I bumped this up to 40-41 psi (tires max are 44psi)
- I moved the crossbars of the roof rack to the very back of the vehicle, hoping it to act as a spoiler of sorts. Since the Jeep has a vertical backend, I hoped that placing both bars back might help drive air into the vacuum behind the Jeep and create less drag
- I kept rpms < 2000 the whole time
- I used "engine-on neutral coasting"

I'll explain the neutral coasting briefly. I read someone else's post recently about trying to coast on downhills, towards red lights, or off exit ramps by shifting their automatic into neutral. I tried this out a bit and am noticing that the Jeep feels as if there is less rolling drag. My suspicions were that disengaging the drivetrain while coasting creates less rolling friction within the transmission, so you can roll further and with less rapid loss of speed.

I filled up last night after having also done a few days of city driving. Total miles driven was just under 300 on 15.5 gallons. My calculated mpg?

....19 mpg. +4 over combined EPA rating. And I was using the AC.

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Old 07-09-2008, 12:24 PM   #2 (permalink)
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w00t! Good job.

Yes, by coasting in neutral in an automatic you save the resistance of the engine on the transmission. I can coast ~4 x further in N than D.
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Old 07-09-2008, 12:33 PM   #3 (permalink)
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Old 07-09-2008, 01:15 PM   #4 (permalink)
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Nice work. That's a hefty increase.

Re. the roof racks: unfortunately, the only thing you can do with the cross bars to improve aerodynamics is to remove them. Moving them to the rear won't help the overall situation.
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Old 07-09-2008, 01:23 PM   #5 (permalink)
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Great Start What's next a little aero modding?

I did a grill block on mine so far. Been trying to find time to make an under body tray.

Seems like the number of cherokee's on this forum is growing
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Old 07-09-2008, 01:42 PM   #6 (permalink)
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Old 07-09-2008, 03:00 PM   #7 (permalink)
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I've been doing the Nuetral coasting as well the past 2 days. Certainly does help a good bit it seems.
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Old 07-09-2008, 07:14 PM   #8 (permalink)
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Quote:
Originally Posted by FastPlastic View Post
Great Start What's next a little aero modding?

I did a grill block on mine so far. Been trying to find time to make an under body tray.

Seems like the number of cherokee's on this forum is growing
It may have been posts by you or by DPOV that I found on Google that lead me to ecomodder.com in the first place. I had recently seen the hypermiling article in USA Today, and started doing my own personal research (I'm a medical student, and an uber nerd. I try to validate anything I see in the news with my own researching ).

My next steps are likely to do a partial grill block (your threads are helpful on this!). I want to get my bumper replaced; it's slightly bent, and the right bumper flare is broken off. I'm sure I can improve my aero by fixing that. I am really interested in a front air dam to push air lower and around the Jeep, and I think I've got a great idea for how to do it without it having to be permanent (and can go on/off in under 5 minutes!). I'll share that soon....

Re roofracks: I do want them off. They are tricky just looking at them, though I didn't try too hard to find a tool to fit the star-tip bolts hiding inside the longitudinal rack mounts. I have just looked a little at different kammback aeromods on the forums, and wondered how a plexi partial kammback might be set to mount on those racks. If you built it just right, it might be retractable back over the roof when not deployed on long highway trips. Input on this one highly welcome.
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Old 07-09-2008, 08:25 PM   #9 (permalink)
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Wouldn't that cause excess wear on the auto transmission?
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Old 07-09-2008, 09:31 PM   #10 (permalink)
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Quote:
Originally Posted by DoctorP82 View Post
It may have been posts by you or by DPOV that I found on Google that lead me to ecomodder.com in the first place. I had recently seen the hypermiling article in USA Today, and started doing my own personal research (I'm a medical student, and an uber nerd. I try to validate anything I see in the news with my own researching ).

My next steps are likely to do a partial grill block (your threads are helpful on this!). I want to get my bumper replaced; it's slightly bent, and the right bumper flare is broken off. I'm sure I can improve my aero by fixing that. I am really interested in a front air dam to push air lower and around the Jeep, and I think I've got a great idea for how to do it without it having to be permanent (and can go on/off in under 5 minutes!). I'll share that soon....

Re roofracks: I do want them off. They are tricky just looking at them, though I didn't try too hard to find a tool to fit the star-tip bolts hiding inside the longitudinal rack mounts. I have just looked a little at different kammback aeromods on the forums, and wondered how a plexi partial kammback might be set to mount on those racks. If you built it just right, it might be retractable back over the roof when not deployed on long highway trips. Input on this one highly welcome.
Glad to hear my posts might be helping spread the word out to other Jeep owners.

The grill block is pretty easy to do with the 7 slot jeep grills. Making separate panels for each slot is a little harder but I found over the summer it was getting a little warmer then I wanted, so the setup made it quick and easy to improve the cooling. I figure over the winter I may fill all 7.

I'm very interested in seeing what you have in mind for the front air dam. I had been pondering making one for mine. I was thinking about setting it up to flip down. Make it an L shape so it's always about 1in tall, but for highway trips it could be flipped down making it 3-4in tall.

The roof racks are easy. I had a $20 tool kit from Wal-mart that included the star key for the screw driver. The sets nothin fancy but seems to have a lot of what I need for the Jeep. I went ahead and just took the cross bars off. I kinda like the looks of the side channels, Plus I didn't figure the side channels would really make that big of a difference anyway.

I've also been wondering about a small kammback. I've been noticing on a lot of newer suvs these small kammback looking panels on the back. Just wondering if that would be something that could be set up on the cherokee? I liked the looks of all the ones I've seen. Ford edge/Rav4 etc.

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