Topic: Gas Mileage Thread

[Wrench]

I have been getting around 12-13 on the highway, but I think that is due to a worn-out carb that doesnt atomize the fuel well.

'84 Cherokee 2.5, carbureted, AX5, 33" tires, 4.88 gears.

[Jeffy]

So after after doing a 400 mile road trip, I've got some new numbers.  With a headwind and driving 70-75 mph, I get around 15 mpg.  If there is no headwind and I drive 60-65 mph I can get about 19-20 mpg.  No A/C this time.  Seeing the numbers I don't think A/C makes that much of a difference.  The real killer is the wind resistance.

 At 70-75 the Jeep gets a little sketchy in that you can feel the wind tossing the Jeep around.  Though it settles as you slow to below 70 mph.  My only real complaint is that my gas gauge doesn't always work so I'm using the trip meter to gauge how much as I have.  Problem is I usually have 4-6 gallons left in the tank when I'd rather have it closer to 2-3, about what's left when the gauge is on E.

There were two places where there were steep hills steep enough to have big rigs crawling at 40 mph, where I had to downshift into 3rd and rev it up (4K RPM) to hold 60 mph for several miles.

[jfrabat]

I'd rather have it closer to 2-3, about what's left when the gauge is on E.

Maybe in YOUR rig...   

[motorhedfred]

There's been some talk about hydrogen as a suppliment to gasoline on this thread and I'd like to add my 2˘. Most units are homemade as the commercial ones look the same as what you could put together from the isles og the Home Depot with a label on it. There's not much research data availible to the general public so we'll just consider this a fun experiment that might save you at the pump (or not).

One of the reasons people don't see the gains they were hoping for on fuel injected vehicles is they're not isolating the oxygen from the hydrogen. If you vent the oxygen to the atmosphere, the O2 sensors don't pick it up and therefore the ECM doesn't compensate with more fuel. Burning the hydrogen only richens the mixture as far as the O2 sensor is concerned which causes the ECM to pull fuel OUT to compensate.

While an HHO generator that can isolate the oxygen and vent it isn't as efficient because you need more space between the negative and positive sides, the difference in fuel economy should be substantial. One downside is, the hydrogen gas does displace some of the incoming atmosphere, but most onboard on demand type systems don't produce enough volume of gas to worry about that factor.....especially if you're not piping the oxygen into the intake. Water IS 1 part oxygen to 2 parts hydrogen after all !

MHF

[sharpxmen]

you're right with the gains
but... theoretically, there's nothing wrong with pumping oxygen, you just press the gas pedal less (less need for oxygen from air) - remember that your fuel flow is related to the demand of power at a specific load, if you make power with something else then less need for gasoline+air (same thing with hybrids, the electric motor provides additional power so less need for fuel at times, or if you with going downhill - you can sustain the same speed with less gas pedal), but besides that you're right - all the on board H generators are not feasible, you replace the gasoline with some other fuel and it's not free regardless, plus it is probably negligible as far as quantity produced like you said.

[RickBrins]

With 240,000 miles on my 95 yj, I am consistantly around the 15 to 16 mpg mark, 50/50 hwy and city.  When I bought it at 80,000 miles 13 years ago, I put the 4.0 thtl body and spacer on it, I also added a K&N to the stock air box, with the front venturi removed. I had a Borla header, then stock manifold, now pacesetter header, open cat and free flow exhaust.  I'm now running 30x9.5 BFG's no lift, but have not noticed much difference over the 215 or 225's that were on it when I bought it.

I always do my calculations based on fill up gallons and miles on the odometer.  I do get some fluctuations as the winter and summer gasses change over and depending on top on or off.

These numbers are also very close to those I used to get on my sadly missed CJ-5 with the 258 inline 6, very slightly lifted with 31 x 10.5's and a light bar.

My 2.5 is apart and headed to the machine shop preparing for a rebuild.  Any thoughts on internal changes to improve MPG will be appreciated, until it is buttoned up and back in.    If I go back to stock, I will be curious to see how much a fresh build helps the power and MPG, but I would be happier to make some proven changes.

[Jeffy]

Well, I've decided to do an update.  After doing a basic tune-up on my jeep, ignition, injectors, plugs, oil change, rotated and checked tires, etc...  (I also lowered it 1.25".  Oh and took the panel off the airbox.  This made a difference by moving the torque to the 2K-3K range.)  I was able to take it on the road for an extended drive.  About 160 miles each trip.  On the first trip, yes I did the same trip twice, I got around 22-23mpg.  The second trip I drove a bit more aggressive and got 20 mpg.  I have driven this route once before many months ago and got 16 mpg.  I'll have to wait for next year to do a 600 mile road trip.

[tucked]

13mpg is what I'm averaging... Less if trying to do highway speeds into a headwind!   

1995 Wrangler YJ
5-Speed
AMC 2.5L TBI
31x10.50x15" Mud Terrains
4.10
Speedometer Calibration - No
NO ENGINE Mods

[Jeffy]

If you haven't recalibrated your speedometer then you're probably getting a bit better then that.  Although stock gears and 31's are a big jump from the stock 205's.

[95 Lowbuck]

1995 Jeep YJ Rio Grand, soft top, 174k miles
Completely stock motor, 5 speed, D44 rear, 4.88 gears.
TJ front axles. (front turning all the time)
33-10.50 BFG KO2’s.(25-30 psi)
No speedo calibration, but pretty close.
4” lift.
I get about 15 city, 17 hwy if not in the mountains.
One thing I want to comment about is the new KO2’S.
Although still a 2 ply side wall, I really like them compared
to the KM2’s I had on it.
Quieter, better riding, better mpg, and superior in any snow condition.
Time will tell how well they work in the rocks,
but aired down with the extra siping, and aggressive side wall tread,
I think they will do well.