Registered: Oct 2004
Location: Omaha, NE
Posts: 974

HYPOTHESIS: Is fuel mileage worse at 78mph versus 65 mph?
(I could not drive at 55mph for fear of being rear-ended! Also above 80 mph is risky for getting speeding tickets! So the data you see is from between 65 vs 78 mph).

2001 Ody LX 65K miles
Omaha, NE- Chicago trip (460 miles/each way)
-New spark plugs Bosch Platinum
-2 adults & 4 kids (under 13 yrs old): Weight about 550 lbs total
-Standard cargo: one ice cooler and 6 bags of baggage of clothes
-Tires 40 psi
-AC on entire trip
-New Brakes Front, so no brake drag or problems
-Alignment done 2 weeks ago.
-Weather 60F, non-windy (at most 5 mph wind)
-Gas is Octane 89, fill and stop filling gas at first “click”.
-Cruise Control used 90% of the time as much as condition allows safe use of cruise control.
-I “zeroed” the odometer at each fill-up to ensure accurate readings between fill-ups

EASTBOUND:
65 mph 288 miles/12.1 gallons = 23.80 mpg

75 mph 221 miles/9.41 gallons = 23.48 mpg

WESTBOUND:
78 mph 381 miles/16.09 gallons = 23.68 mpg


My point is between 65 mph and 78 mph, there is very little drop, if any, in fuel economy (in contrast to government data which indicates a drop of approx. 7 mpg or so between 65 and 78 mph)

MY “CONCLUSIONS”
1. Government data may have been obtained from cars from 80’s and 90’s, which were possibly less aerodynamic.

2. 2001 Honda Odyssey has very good aerodynamic shape (almost like an airplane tip) and the fuel mileage may be different than this:
http://www.fueleconomy.gov/feg/driveHabits.shtml
I suspect the “significant” drop happens after 80 mph for Ody (but I cannot prove it because of speed limits!).

Of course, an airplane has a differnet fuel mileage curve.

3. The drop in fuel mileage between 65 vs 78 mph was negligible, if any. (BTW I do not have 55 mph data, reason as above).

4. I did this experiment simply to prove my point. I do NOT encourage speeding, please follow posted speed limits.

***NOTE: This is as good as data set as I can get.

*** Also, the shape of the fuel mileage curve is different for each vehicle.

I am looking for sharing highway Fuel Mileage data in an honest fashion so we can all learn about Ody characteristics.

Anyone with another set of data will be appreciated!

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cnn: 2007 Odyssey LX 30K miles

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Registered: Jan 2002
Location: Brentwood, TN
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I have a 2001 also, but haven't done any tests like that. It would be interesting to hear what others may have found.

I would, however, be leery of relying on such a limited data set. You are relying on only three fillups, and there are most likely variables in each that will skew your results. The most obvious variable is stopping each fillup at the first click, rather than topping off as much as possible to ensure accurate measurements. It's highly unlikely that all three gas pumps were manufactured by the same company and were calibrated exactly the same, and thus probably stop at different points. If each clicked off at different points in the fillup you are not starting with the same quantity of gas in the tank.

Your hypothesis may very well be correct, but you might want to try your tests over a larger number of fillups before coming to a conclusion.

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Current Hondas:  2005 CR-V EX-SE, Pewter Pearl; 2001 Odyssey EX-NAVI, Starlight Silver
Previous Hondas: 1997 Accord EX-L Forest Green; 1992 Accord EX, White; 1982 Accord DX hatchback, Silver
Hobby:  geocaching

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Registered: Oct 2004
Location: Omaha, NE
Posts: 974

quote:

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Originally posted by Steve P
I have a 2001 also, but haven't done any tests like that. It would be interesting to hear what others may have found.

I would, however, be leery of relying on such a limited data set. You are relying on only three fillups, and there are most likely variables in each that will skew your results. The most obvious variable is stopping each fillup at the first click, rather than topping off as much as possible to ensure accurate measurements. It's highly unlikely that all three gas pumps were manufactured by the same company and were calibrated exactly the same, and thus probably stop at different points. If each clicked off at different points in the fillup you are not starting with the same quantity of gas in the tank.

Your hypothesis may very well be correct, but you might want to try your tests over a larger number of fillups before coming to a conclusion.

---

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cnn: 2007 Odyssey LX 30K miles

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On the calibration of gas pumps, I think that has more to do with ensuring that the amount of gas delivered matches what is charged for.

I suspect that the automatic shutoff mechanism varies between different gas stations and gas pumps, and that's what I was thinking about being a big variable in how full the tank actually gets at a fillup. I like tracking gas mileage and always try to top off my tank for accurate measuring. Despite all the posts here on why one shouldn't do that because of a charcoal canister, I've topped off tanks since I owned my first car in 1979 and have never had a problem.

I was curious how a gas pump knows when to shut off when the tank nears the full point, and found this:
http://www.straightdope.com/classics/a1_263.html

As to your original point, it sure would be good for Honda to include an instantaneous MPG readout as I have seen in some other cars. That would make it very easy to see where gas mileage peaks, and how rapidly it drops off at various speeds. A former boss of mine back in 1985/1986 had a Cadillac with an analog MPG meter. She said the car would get its best mileage at 55 MPH.

Thanks for your observations.

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Current Hondas:  2005 CR-V EX-SE, Pewter Pearl; 2001 Odyssey EX-NAVI, Starlight Silver
Previous Hondas: 1997 Accord EX-L Forest Green; 1992 Accord EX, White; 1982 Accord DX hatchback, Silver
Hobby:  geocaching

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Registered: Oct 2004
Location: Omaha, NE
Posts: 974

quote:

---

Originally posted by Steve P
On the calibration of gas pumps, I think that has more to do with ensuring that the amount of gas delivered matches what is charged for.

I suspect that the automatic shutoff mechanism varies between different gas stations and gas pumps, and that's what I was thinking about being a big variable in how full the tank actually gets at a fillup. I like tracking gas mileage and always try to top off my tank for accurate measuring. Despite all the posts here on why one shouldn't do that because of a charcoal canister, I've topped off tanks since I owned my first car in 1979 and have never had a problem.

I was curious how a gas pump knows when to shut off when the tank nears the full point, and found this:
http://www.straightdope.com/classics/a1_263.html

As to your original point, it sure would be good for Honda to include an instantaneous MPG readout as I have seen in some other cars. That would make it very easy to see where gas mileage peaks, and how rapidly it drops off at various speeds. A former boss of mine back in 1985/1986 had a Cadillac with an analog MPG meter. She said the car would get its best mileage at 55 MPH.

Thanks for your observations.

---

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cnn: 2007 Odyssey LX 30K miles

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Registered: Mar 2005
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I think your MPG numbers are very interesting.

But, as noted above, you might need many more test runs to establish the effect of speed on mileage. I tracked the MPG of my Prelude for well over 300,000 miles of driving and I would often see changes in MPG for which the causes were not immediately apparent. I'd always fill the tank carefully and I'd often drive the exact same route over and over again.. So YMMV. ;-)

The aerodynamic drag of the Odyssey, or any vehicle, at 78 MPH is 44% higher than the drag at 65 MPH. (The drag varies with the square of speed.) So I guess one question is how much of the Odyssey's total resistance to forward motion is due to aerodynamic drag. The Odyssey appears to be fairly well designed but it's still a pretty boxy shape. I'd love to see some drag coefficient data for it.

Other potentially significant factors would include engine efficiency versus load and RPM, and rolling resistance.

Anyway, I find this topic very interesting.

Thanks for posting your results.

Bob

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Registered: Apr 2005
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I make frequent trips between Chicago and Cincinnati. I run between 80-90 mph depending on traffic. The Ody is always in the 23-24 mpg range. In fact, that is what I have been getting since I've owned it and got it new. When we would go from Norfolk, VA to Cincinnati (about 675 miles) it didn't matter if we were going 85 up the mountains or on the flats, it averaged about 23-24 mpg over a tank. Mine is a 02. For those who might be concerned about the validity of my data, my tests are totally unscientific and I could care less about how the pump is calibrated much less if has been calibrated. I know my bank account is calibrated and I pay more and get less for gas.

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Registered: May 2006
Location: portland,or
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quote:

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Originally posted by BobF
I think your MPG numbers are very interesting.

But, as noted above, you might need many more test runs to establish the effect of speed on mileage. I tracked the MPG of my Prelude for well over 300,000 miles of driving and I would often see changes in MPG for which the causes were not immediately apparent. I'd always fill the tank carefully and I'd often drive the exact same route over and over again.. So YMMV. ;-)

The aerodynamic drag of the Odyssey, or any vehicle, at 78 MPH is 44% higher than the drag at 65 MPH. (The drag varies with the square of speed.) So I guess one question is how much of the Odyssey's total resistance to forward motion is due to aerodynamic drag. The Odyssey appears to be fairly well designed but it's still a pretty boxy shape. I'd love to see some drag coefficient data for it.

Other potentially significant factors would include engine efficiency versus load and RPM, and rolling resistance.

Anyway, I find this topic very interesting.

Thanks for posting your results.

Bob

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Registered: Oct 2004
Location: Omaha, NE
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quote:

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Originally posted by renew82
I make frequent trips between Chicago and Cincinnati. I run between 80-90 mph depending on traffic. The Ody is always in the 23-24 mpg range. In fact, that is what I have been getting since I've owned it and got it new. When we would go from Norfolk, VA to Cincinnati (about 675 miles) it didn't matter if we were going 85 up the mountains or on the flats, it averaged about 23-24 mpg over a tank. Mine is a 02. For those who might be concerned about the validity of my data, my tests are totally unscientific and I could care less about how the pump is calibrated much less if has been calibrated. I know my bank account is calibrated and I pay more and get less for gas.

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cnn: 2007 Odyssey LX 30K miles

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Registered: Apr 2005
Location: Gurnee,IL
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cnn,
I was going to mention that I'm surprised that the motor in your van hasn't blown up or you melted a piston cause you installed Bosch plugs and the tranny hasn't fallen out cause you have unauthorized fluid in it. I find it funny all of the fear and loathing that goes on around here. You make a simple post to share information and get questioned on your methodology like you were writing a research paper for post graduate physics.


Take it easy and thanks for your efforts.

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Registered: Mar 2005
Location: California, USA
Posts: 118

quote:

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Originally posted by cnn
Admittedly, when I did the test I did not have the gut to drive at 55 mph (rear-ending risks!!!), rather my data came from 65-78 mph range.

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quote:

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Originally posted by Steve P
I suspect that the automatic shutoff mechanism varies between different gas stations and gas pumps, and that's what I was thinking about being a big variable in how full the tank actually gets at a fillup. I like tracking gas mileage and always try to top off my tank for accurate measuring. Despite all the posts here on why one shouldn't do that because of a charcoal canister, I've topped off tanks since I owned my first car in 1979 and have never had a problem.

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Last edited by BobF on 05-24-2006 at 03:36 PM

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Registered: Nov 2003
Location: Sharon, PA
Posts: 5982

No suprise here..On the highway..Mine seems to do the same between 65 and 85

My Altima..I took a 200 mile trip and never made it under 90 once on the highway and averaged 30

Once rolling..It does not take much gas to maintain speed

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04 Odyssey (9.67mpg mix) 27mpg Highway- Go figure
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91 MR2
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Registered: Mar 2002
Location: Location, Location
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quote:

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Originally posted by cnn
2. I posted similar info in the 3rd Gen Ody and almost got "killed" by some people

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2002 EX - Transmission replaced at 84,000km (52,000 miles). Sold at 104,000km.

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quote:

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Originally posted by Grand Total
Part of the reason you almost got "killed" is because you dressed it all up with pseudo-science to try and justify your beliefs. You may (or may not, I don't care either way) have a Physics degree, but don't try and BS people here and no one will "kill" you.

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cnn: 2007 Odyssey LX 30K miles

Last edited by cnn on 05-24-2006 at 04:40 PM

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