Fuel consumption!!!!!

[dodge2002]

They say that the 2002 caravan go 18 mpg in city.

Well, mine do about 13 and I don't drive agressively.

Anyone with the same problem?

[bluer101]

My 2005 GC SXT only gets around 14-15 around town.

[gas28man]

Did you recently buy new tires that are different size than stock, specifically, a little larger? I have a 96 Caravan that consistently got about 24 on the highway, even now with 253K miles on it. My tire guy got me a deal on a pair of tires for the front that were slightly smaller profile and I watched my gas mileage go almost to 27 on the highway. That was great until I rotated them to the back, and it went back to 24 mpg.

[Lscman]

Is that in a metro city with constant stop and go and nasty traffic jambs? I know some folks that take 30 minutes to travel 10 miles during rush hour. This is hardly city driving. An efficient econobox commuter vehicle gets 0 MPG when it's stationary and single digit gas mileage when creeping along at walking speed.

Do you leave the trans in D or OD?

[Lscman]

Did you recently buy new tires that are different size than stock, specifically, a little larger? I have a 96 Caravan that consistently got about 24 on the highway, even now with 253K miles on it. My tire guy got me a deal on a pair of tires for the front that were slightly smaller profile and I watched my gas mileage go almost to 27 on the highway. That was great until I rotated them to the back, and it went back to 24 mpg.

I thnk the point to your post is....

gas mileage calculations are influenced by odometer error. You actual gas mileage, in fact, did not significantly go up or down when you changed tires. Efficiency hardly changes, & if anything, it improves with larger dia tires. With smaller tires, your odometer tells you that you've traveled farther than the actual distance...yet you used the same amount of fuel. With larger diameter tires, your calculations are probably closer to actual. The mfr typically calibrates odometers and speedos to read 3-5% high, so fuel usage calculations are off by the same amount. If the diameter of your tires is 3-5% oversize, the fuel consumption calculation will be more accurate.

[AMD Rules]

The mfr typically calibrates odometers and speedos to read 3-5% high
Do you have literature that support that claim ?

I was not aware of that. I find it hard to believe that in an industry that leads the way in terms of quality programs (ISO or QS9000 etc) and initiatives towards providing calibration procedures that ensure accurate manufacturing tolerances would adhere to a guage calibration procedure that is technically 'incorrect'. 3 to 5% is a huge tolerance range to overshoot.

I do understand the principle behind your claim, is to ensure the speed errs onthe conservative side, and leads the driver to believe they are moving faster than they actually are (less traffic court appeals), but cannot understand that false calibration is acceptable. Not much use in having a guage that is not accurate. Its like setting a clock ten minutes early to ensure you are on time for appointments. Doesn't make sense.

[dodge2002]

My trans only have OD.
I'm driving in Miami

[gas28man]

Oh, I'm well aware of the science behind it all. I'm just reporting what the little on-board computer was telling me. I know it wasn't accurate. I only raised the point because I wasn't sure if the person who started the thread was aware that changing the tire size will change what the on-board computer reports, without actually producing a corresponding change in consumption per mile traveled.

[james86-951]

3-5% variance is considered statistically valid.

[Lscman]

Do you have literature that support that claim ?

I was not aware of that. I find it hard to believe that in an industry that leads the way in terms of quality programs (ISO or QS9000 etc) and initiatives towards providing calibration procedures that ensure accurate manufacturing tolerances would adhere to a guage calibration procedure that is technically 'incorrect'. 3 to 5% is a huge tolerance range to overshoot.

I do understand the principle behind your claim, is to ensure the speed errs onthe conservative side, and leads the driver to believe they are moving faster than they actually are (less traffic court appeals), but cannot understand that false calibration is acceptable. Not much use in having a guage that is not accurate. Its like setting a clock ten minutes early to ensure you are on time for appointments. Doesn't make sense.

May not make sense...but it is true. I tested vehicles for Chevron & EPA for several years. Instrument cluster accuracy with factory tires varies by brand an model. The most optimistic speedos are found on Audi, BMW and Porsche. They run around 8% fast.....some push 10% error. The least optimistic is Ford...they read about 0 to 3% fast. Other domestics fall in the 2%-5% fast range. With all the legal ramifications these days, it behooves the manufacturers to allow for variances in tire diameter and pressure. They don't need dragged into court because some ambulance-chaser got a ticket for speeding. The radius of a tire becomes significantly larger at extreme temps and diameters can vary about 1" between brands. Keep in mind too that a tire will get smaller as it's 11/32" of tread gets eaten away.

[AMD Rules]

I learn something new every day (I hope). Thanks for the info. :SPIN:

[dodge2002]

Thanks for the replies.
I'm not using the on-board computer to find out about my miles per gallons. I know it's not accurate.
I'm using the actual mileage per fill-ups it is more accurate.

[Creepingdeath]

My '97 gets about 17 mpg, but I also use it for a paper route I have. 7 days a week. I thought that was pretty damn good for a lot of stop and go driving.

[Lscman]

My 4000lb 3.3L '01 Grand Caravan does fair....about 17 city & 25 highway. This was a good improvement from the 16 city and 20 highway I got with my old 4L 4WD Aerostar.

That said, these are about the same efficiency numbers I see with my 3700lb 4.4L V8 4dr 540i BMW and my 3300lb 5.7L V8 Corvette. Both have 6spd sticks....the manual trans, gearing and weigh serve as offsetting penalties.

The Caravan does a heck of a lot better than most conventional SUV's....and it hauls cargo & passengers as comfortably as a huge Expedition or Suburban.

[507corey]

It seems as though some people can't focus on what your original problem was, so let me echo it. I recently purchased a '99 Caravan with a 3.3 and I feel like my mileage is insufficient as well. The best we can get on long trips is about 18 mpg. Can someone give some input?

[mmahamm]

Tire sizes and odometer error aside, the city mileage someone gets can vary tremendously based on where you are driving. When I fill up my tank, I reset the trip computer. When I first start out, if I hit a lot of red lights, I am lucky if it will go above 10 mpg. If your driving is - very - slow - with a lot of sitting and idling in very heavy traffic, it is perfectly understandable that your city mileage would be below 15 mpg. Nothing you can do about it other than move.

Highway mileage only about 18 sounds kind of low, but again, conditions are important: You will get much better gas mileage at 55 mph than you will at 70 mph. My 95 Plymouth Grand Voyager had a 3.3L V6 and a 4-speed transmission, and consistently got 19-20 on a weekly basis (combined city and highway), and only went up to 22 or 23 on the highway. I am convinced I could have done better on the highway if the van was empty, but every time I was on the highway I had a full load, so I never got to test my theory.

In my wife's car last year, I traveled from Northern Virginia to Greensboro, NC and back one weekend. On the way down, I didn't pay much attention to my speed. On the way back, I was careful to stay within 5 mph above the posted speed limit, and tried to accelerate only on downgrades and avoid downshifts going up hills (when there was no traffic that would be annoyed by the latter). I got about 2.5 mpg better on the way back. Saved about $5 in gas on that trip!

[mloaks]

No speedo and odo is as optimistic as those in Italian cars and motorbikes, at least by my extensive experience! ;cP
Our 3.3 SE gets about 20 mpg in small town driving, 23 on a trip. Yours is a bit low...