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Old 09-20-2017, 05:51 AM   #1 (permalink)
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34MPG in a 2002 Grand Cherokee diesel

Hello everyone!
I've had a topic in the past about my old car, a diesel Cherokee XJ, which ended up grenading the engine and was replaced by something heavier and automatic, which doesn't sound like would have better economy. A 2002 Grand Cherokee with the same drivetrain as the 2002-2006 Sprinters sold in North America.

In the recent years I've driven it 40k miles and had quite a few long highway trips on the same roads, so I could test and compare the economy. All tests are done in the same section of road, 645km total, with 220km of national roads (villages, passing slower cars etc).

Best tanks on the first two summer trips:
8.1 liters / 100km (29.04 MPG), same as advertised.

Then I installed a front lip and lower grille cover and the best MPG on a winter trip:
7.4 liters / 100km (31.78 MPG)

The lip got messed up in storage and I installed a different one and plugged some holes around the radiator, as it was summer and I did not want to cover the entire lower grille:
7.43 liters / 100km (31.65 MPG)

Next was a full section of highway in Austria and Germany, including passing semis, some driving done at 75mph while 90% of the time it's stuck at 60mph () as for all trips and managed a personal best:
6.89 liters / 100km (34.13MPG).
I filled up to the first click of the nozzle, it seemed strange to use that little fuel, then filled up again and added 3 liters of fuel.

Some pictures right before the last trip, please ignore the messed up front bumper:






What next? Some side panels for the lip to cover more of the tire? Rear tire spats? Some sort of rear spoiler? Definitely not another car as this is my weekend warrior to keep up with Wranglers on trails and when called for hauls it's decent share of stuff.

In February I will be going to Austria again, so I can test my highway mileage again.

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Old 09-20-2017, 11:34 AM   #2 (permalink)
It's all about Diesel
 
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That's a cool rig. Considering the improvements on fuel-efficiency that a direct-injection engine usually has, compared to the indirect-injection one fitted to your previous ride (which is only advantageous while running vegetable oils as an alternate fuel), how much of a difference did you feel between the fuel consumption of both?
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Old 09-20-2017, 01:43 PM   #3 (permalink)
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Thanks! It's getting way more use than the old one. Offroad I have no fear keeping up with stock Wranglers.

I never managed to get a mileage calculation for the old one, as the engine grenaded on the only long-distance trip I did with it. But people report 28-29MPG on the highway, so same as this one without the aero mods and driving it at the same average speed.

This new one gets worse mileage around town due to the automatic and extra 700 lbs.
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Old 09-21-2017, 12:02 AM   #4 (permalink)
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Sure the automatic does decrease the fuel-efficiency in city traffic. But how does it compare between those rides? I could presume the higher tech of the engine fitted to your current ride may offset this disadvantage a little.
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Old 09-21-2017, 03:26 AM   #5 (permalink)
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On the highway the rated fuel consumption is very close. Other than that I did not keep fuel consumption data for the old Jeep to compare.
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Old 09-21-2017, 06:01 PM   #6 (permalink)
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Clearly aero improvements are working for you. That's really impressive results for that big box.
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Old 09-22-2017, 03:35 AM   #7 (permalink)
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Thanks!
I want more. So I guess some side panels for the lip to cover more of the wheels are in order.
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Old 01-20-2018, 03:48 AM   #8 (permalink)
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Prototype for the airdam extension to cover the wheels. This is how exposed the wheels are


Prototype out of cardboard:



How does that look? Should the edge of the dam be a bit rounded?
Testing the same route as the other tests will happen in two weeks, until then I can only test with the instant fuel consumption and the injection quantity from the scan tool.

Sorry for the huge pictures, it seems like I can't resize on mobile.
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Old 01-20-2018, 10:28 AM   #9 (permalink)
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Thinking maybe a little less on the width maybe align it with the last groove of the tire. Just speculation on my part as most I see don't go to the edge of the tire. How far off the ground is the bottom? Don't forget about curb stops and driveway angles. Maybe others will chime in.
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Old 01-20-2018, 12:04 PM   #10 (permalink)
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Maybe angle it back some to direct the air around the tire some, that would allow you to not need it to be so wide, reducing surface area.

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