Project Grand Cherokee Thule Fairing?
 

Hey all:

Am a new member and in need to try to improve the gas mileage on my 2004 Grand Cherokee (I know, sell it and buy a honda- not an option).

I have a Thule Rack and got a free Fairing (#555) for it. Right now, I get 15.1 MPG, will post what I get with the fairing, hoping to help it, at least a bit. Also planning on installing a lightweight skid plate like another member did on their cherokee, will post those results as well.

Question for you all is if anyone out there has a #555 fairing, could you measure your struts, please? Thule does not sell them anylonger, and anyway, I want to try to make them.

If you check out "I" on this image, that's the strut.

Thanks all, and looking forward to posting better mileage through aero-tinkering!

Welcome!

I'm thinking that will be good for maybe +1 mpg. You could do so much better by looking into some hypermiling options, so I encourage you to do so!

And with a cherokee, you will see much more dramatic improvements if the majority of your driving is done in the city.

good luck!

Welcome to the site. Lots of Jeep owners to bounce ideas off.

Does the rack live up top full-time?

Change your driving style first :)

jeep
 

thanks, all. Yes, I have been doing the hyper miling suggestions and changing my driving style, just want to take it to the next level and "tinker" a bit.

the rack does stay on full-time, although does anyone have info on how much I can gain by taking it down and just storing it?

You're taking a significant hit from leaving it up there when it's not in use.

Mini-experiment: the wrath of roof racks - MetroMPG.com

These roof racks:

http://www.metrompg.com/posts/photos...tb-2view-z.jpg

... reduced my MPG by 12% at 55 mph - empty. With the bike in the rack, mpg dropped 27%.

Obviously not directly comparable to your vehicle, but as a rule you should avoid carrying things on top of a vehicle if at all possible.

roof fack wrath
 

case closed, I removed them tonight.

15.1 MPG

Just changed spark plugs and removed rack, will post in the next few weeks where I am at.

The bonus is that if you do put the rack back on when you need it, the fairing should help slightly :thumbup:

2004 Cherokee V8 Results
 

So, its been over 2 weeks, and when I started, my fuel economy was 15.1 MPG. I did all of the following:

1) Removed a Thule Roof Rack alltogether
2) Drive according to most Hypermiling suggestions (slow start, keep it under 2k revs, coast, draft, etc.)
3) Replaced my air filter and spark plugs
4) Remove all excess weight from the car
5) Checked the tire pressure.

After two weeks, I am still clocking 15.1, so it is clear to me none of the above worked, unless (a) I need more time for the onboard diagnostic tool to record any saves, or (b) these "fixes" do nothing for V8 S.U.V.s.

Any one have an idea?

I'm going to suggest the problem is in your data collection/comparison, simply because modifying driving habits alone will result in significant savings, guaranteed.

When you say you were getting 15.1 "before", are you talking about a single tank? Your vehicle's "lifetime" MPG average? Was 15.1 before making any changes, including to your driving technique? Are you comparing the exact same route, same accessory loads (e.g. air conditioning) and traffic conditions?

The 4.7 probably doesn't care about those two. I know my 4.0 doesn't

Most likely you are looking at your number off of an computer on the car. You should calculate your MPG manually (miles/gallons) at the fill-up. Um, if you are doing it manually then never mind my post. :o

Yeah, be very wary of those built in gauges, my mom's Chrysler will read as low as 18 running down the freeway at the speed limit (EPA rated at 24 highway, of course, my mom wastes gas like it's her job too...)

The only instruments that count are the odometer (check it with a GPS if you can) and the fuel pump.

The electronic thingies are OK for detecting changes but in general are electronic politicians.

A ScanGauge or MPGuino used in controlled circumstances - mutiple, speed-controlled, bi-directional A-B-A runs, on an empty road - is the best method of measuring a mod's in/effectiveness.