West Desert Utah checking in...
 

Where to begin... First off, I drive a 1995 Jeep Grand Cherokee. Currently getting 20 MPG out of it. I know I can do better, but still, not too bad for a 13 year old station wagon. After lurking and reading decided to sign up, as there is another 95 Grand on the board.

My GC DOES have the overhead console with the economy readout. I had a 94 Chrysler Concorde before that had that feature. I'm sure it is not as instananeous or as accurate as the Scan Gauge I see some using. But it is a far cry better than flying blind. I also use synthetic oil in the motor, will try a different synthetic ATF fluid as soon as I find something safe to use with this transmission. Also, the transfer case has synthetic fluid, and the differentials will be getting synthetics too.

As I've gotten older, I have slowed down, so mileage has been getting better. I commute 100 miles a day round trip, but carpool, so I really only have to drive 1 day a week. Four of us in the pool, working 4 10 hour days. Two ways to save fuel right there.

Yes, I own other vehicles but won't be discussing them for sometime. I'm more interested in doing more for my Jeep at the present.

I do use my Jeep for offroading. I make no apologies for that. I'm in with a couple clubs that do trail repair and maintenance. We are big on trail etiquett and education to keep people on trails. Most people do the right thing when educated. Some can't be taught sadly. And those are the ones that give all of us a bad name.

So back to the Jeep. No, it isn't getting a huge lift nor the biggest tires. I currently ride on 30" tires, but they are relatively narrow. I am thinking about 31" tires in the future. I do not want to go bigger than that because it is my DD and going too big is a killer on fuel. I see that taking my roof rack off could help, are there some real world numbers for that? I do not carry as much stuff in the Jeep during the week as I would for offroading. But I do carry some emergency items, the long commute mixed with where I work make this a must. I do not have subwoofers or other extras.

Because I do take the Jeep offroad, I'm preparing to build solid bumpers for it. I am taking into account airflow and resistance, but do need solid protection too, as well as clearance. Also, I see belly pans of benefit to improve aero, I'm sure I can incorporate some sort of pan with lower body protection too. No reason these have to be mutually exclusive.

I'm curious about using some sort of open source software to be able to model aero/wind tunnel figures. I'd prefer some sort of Linux application.

While I make no apologies for my choice of vehicle or how I use it, I will apologize ahead of time if I ruffle feathers. THAT is not my intention. I have views that may differ from others. I have a right to express those views as others have a right to express theirs. I spent 20 years in the service of my country to help preserve those rights. I am, an acquired taste.

So this is me. Interesting place you have here, I DO very much look forward to learning ways to save fuel/money here.

Greetings and Salutations,
I am a fellow Vet. You are not alone in being outspoken or voicing your opinions. To that I say everyone here has opinions and we are all civil enough to tolerate others. However you may get an occasional taunting. All in good fun for the better of all.

Enjoy, Read, Learn, Input, Do, Test, Re-Input, Share,

I must goto work now.
S.

I retired from the Navy almost 7 years ago (wow, that seems like a lifetime). I've been on other forums where my views were attacked and I was berated. Absolute lack of civility. I've been reading this forum now for a while and have been pleased with the tolerances allowed for Jeeps and trucks. VERY refreshing indeed.

Where I work is remote and lacks cellphone converage so I need to carry some basic things in the vehicle, whether my Jeep or any other vehicle I drive. That means weight. I too have gained a few more pounds than I need and am again trying to lose some. I know that too will affect the mileage.

I know I will never get 30 MPG out of my Jeep. But if I can gain even 1-2 MPG improvement that is indeed something. Hopefully, my introduction wasn't too much, but I do need people to see more of what I am about than just a HI...

I use Ansys Fluent on Linux for CFD. Unfortunately it is not open-source - it is actually the only closed source program on my Gentoo laptop. Being a student and taking a class (in turbomachinery) with a company started by the same mentor as them, I get it for free, though. If you can get it through connections of a student or someone in industry they want to entice into site licenses, I highly suggest you do.

A good open-source CFD solver is OpenFoam. Unfortunately it may be a bit challenging to use if you are not familiar with the field.

Hey thanks for the Openfoam link. I'm still sort of new to Linux, running three flavors on different machines at home. Haven't done any 3D modeling in about 10 years though... I like challenges!

Welcome to the forum, zjrog -

Looking forward to watching your progress. If you're serious - put it on display so the rest of us can follow along. (IE - make a garage entry for your Jeep, and fill out the fuel log.)

Roof racks: there are no hard & fast numbers, because the style differs from vehicle to vehicle. Aftermarket racks are almost always going to be worse than OEM. The *least* harmful aftermarket rack tested and mentioned in Hucho's Aerodynamics of Road Vehicles adds 0.10 to the Cd, which is enormous. Even if your OEM rack is a third of that, it's worth taking off.

When I tested the aero penalty of aftermarket racks empty vs. racks + bicycle on my car, my mileage fell by an astonishing 12.7% - and that's with nothing on the racks.

You'll note that GM has left the racks off its hybrid Tahoe.

I'd say: take 'em off. They're certainly not helping.

cheers-
Darin

OK, in the garage. Will update as I go. Yes, I am serious about gaining mileage. I also know my offroad excursions will cause my average mileage to suffer though. I'll have to figure a way to factor that for the group.

I read your roofrack test with interest. I think I'll carry my bikes on the back of the Jeep. Wonder what that penalty will be? I am also working at droppping some weight off me.

I have some concerns. I know my Jeep runs warm. I'm just not sure I'm willing to block off too much of the grill or the lower grill, since I work and play in the desert. But I'm also considering ditching the belt driven fan for electric fans. Thinking this will be more efficient for cooling and free up some horsepower.

I'm not sure raising tire pressure above the max on the sidewall is safe. I have my reasons for thinking this. But I have played with pressures to get an even tread pattern on the ground for this vehicle. Which gave a great ride and good handling. I've now raised the pressure on all 4 tires. 3 pounds above what I was using. I don't really like the rougher ride yet, as I am finding all my rattles!!!

I do all my own work. I recently replaced the headgasket and waterpump. And I've done full brake jobs front and rear. I'll be learning to weld and stuff.

So, there we go. I'm guessing you haven't been certain if I'm real or a troll. Not a troll.

Roger

I don't tink anybody thought you were a troll, :)

Any way you could just carry the bikes inside the car? I can fit at least two road bikes in my crx so I figger a jeep can do a lot more, right?

Thanks. I didn't get a warm welcome elsewhere. So pardon my own skepticism, please.

As mentioned, I carry a lot of extra stuff out of habit. Living and working in the desert have a way of doing this. Food, water, spare parts and recovery gear. So I don't have a lot of extra space inside. I keep the seats free for the carpool and my family. And sometimes my English Mastiff... So the bikes will stay outside.

Definitely smaller than putting them on the roof, if that's where they rode along before. At highway speeds, the difference will definitely show up at the pumps. If you can remove the front wheels and somehow center the bikes so they don't stick out any wider than the rear of the vehicle, there may be no aero penalty at all, since they'll be sitting in the turbulent wake.

True and true.

Looking forward to watching your progress!