I'm curious to find out what is the most efficient speed for other Smarties.  I've always been told 50-55mph is the most efficient speed.  However while testing out my new guage (and I have no clue if it actually is acurate) it seems to give me the highest MPG reading at 74-75mpg.  Is this right?  I haven't finished calibrating my device yet... so far its at +65%, and seems to read pretty close to my calculated MPG (it reads around 12MPG @45mph before calibrating, which obviously isn't correct), either way the highest reading regardless of calibration should be the most efficient speed, right? What the actual MPG is, well that's another story.

 

Has anyone tested different speeds, preferably with an accurate gauge (ie... scan guage II) to find out which is the most efficient.  I know miles out/gallons in is the most accurate overall... but that doesn't help with the exact speed for peak efficiency.

 

I'm a science teacher, so I like my data, and repeatability/validity of results.  (and am wishing I had the data logger right now... so many variables especially with no cruise control!)

Tags: MPG, efficiency, instant, kiwi, scanguage

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I've been religiously tracking my fuel usage on (http://www.fuelly.com/driver/gidjit) since August 09. I now have 30 fuel ups and have averaged 38 MPG's over the last 7 months. My mileage during the hot months with AC was typically 35 - 36 MPG and now during the cool months I typically get 39 - 40 MPG. 95% of my driving is back and forth to work 40 miles round trip through stop and go traffic. Tracking engine efficiency for me is almost impossible.

Here in Dallas, TX, gas stations have 10% ethanol to help oxygenate the fuel for cleaner emissions. However, this I'm sure also affects my mileage slightly negative. I don't use a scan-gauge but I to like my data. I can't change my driving habits but data logging over time should show me the results of my habits (bad or good).
The gauge definitely helps... 1. to see the sweet spots to drive most efficiently and 2. a VERY steady foot helps. It's almost like it wants to settle into a speed. Hopefully, in the long run the gauge will pay for itself. (as it starts to warm up, I'll really see if it is helping)

CL and TR Fellows said:
I've been religiously tracking my fuel usage on (http://www.fuelly.com/driver/gidjit) since August 09. I now have 30 fuel ups and have averaged 38 MPG's over the last 7 months. My mileage during the hot months with AC was typically 35 - 36 MPG and now during the cool months I typically get 39 - 40 MPG. 95% of my driving is back and forth to work 40 miles round trip through stop and go traffic. Tracking engine efficiency for me is almost impossible.

Here in Dallas, TX, gas stations have 10% ethanol to help oxygenate the fuel for cleaner emissions. However, this I'm sure also affects my mileage slightly negative. I don't use a scan-gauge but I to like my data. I can't change my driving habits but data logging over time should show me the results of my habits (bad or good).
I have been getting 300 mp tank,usualy I'm hi-way driving at 70 mph +.
jaybudder said:
The gauge definitely helps... 1. to see the sweet spots to drive most efficiently and 2. a VERY steady foot helps. It's almost like it wants to settle into a speed. Hopefully, in the long run the gauge will pay for itself. (as it starts to warm up, I'll really see if it is helping)

CL and TR Fellows said:
I've been religiously tracking my fuel usage on (http://www.fuelly.com/driver/gidjit) since August 09. I now have 30 fuel ups and have averaged 38 MPG's over the last 7 months. My mileage during the hot months with AC was typically 35 - 36 MPG and now during the cool months I typically get 39 - 40 MPG. 95% of my driving is back and forth to work 40 miles round trip through stop and go traffic. Tracking engine efficiency for me is almost impossible.

Here in Dallas, TX, gas stations have 10% ethanol to help oxygenate the fuel for cleaner emissions. However, this I'm sure also affects my mileage slightly negative. I don't use a scan-gauge but I to like my data. I can't change my driving habits but data logging over time should show me the results of my habits (bad or good).
I typically don't fill up until I'm below 1 gallon on my fuel indicator. It appears I average about 320 miles/fillup. The temperature here is beginning to get hotter but still in the 80's and I'm enjoying the fresh air. Once the temperature reaches 90 then I'll be rolling up the windows and turning on the A/C. We'll see how my mileage is affected then.
My best was 53 mpg @ 70-75 mph. I've never gotten less than 40, w/ A.C. on in Atlanta traffic.
The Ecometer does the average mpg for the trip, tank, or life of the car. It will keep going until you hit reset. So you decide how long to calculate the average mpg.

jaybudder said:
I have a different gauge than the scanguageII or the ecometer (mine does all the other stuff and more... but the company stinks). I have my efficiency set to 70% right now, but still need to do more tests before I totally trust it. Had been running at 65% but that seemed to low. Unfortunatily mine only counts a trip for engine on to engine off, so I'm not getting a reading for what a tank of gas is getting for mpg. (it shows me averages of my lastest trips, but not an overall) I have not done a test of fill up, drive, fill up to compare the two, yet... I need an excuse for a road trip.

I hear with the scanguage you have to enter your gas amount or something each time you fill up then it somehow recalculates... Don't know if you do this everytime, or just until it is fully calibrated. Even if your efficiency isn't calibrated properly yet, if the reading goes up, the mpg is going up, too, right? Have you tested specific speeds... what consistant speed gets you the highest reading? What do you get @55, 70, 78? (I know it will vary on conditions... just curious how yours reads)

How does the ecometer work? Does it calculate the average for the fill up, or just individual trips like mine? Wonder if efficience is the same on both meters?

Seumas said:
I have an "ecometer" and when I first plugged it in it would tell me I was getting high 40's to mid 50's but when I would fill my tank and do the math the reality was I was getting my normal mpg in the high 30's range(38-39). Then I fine tuned it by setting the efficiency (engine efficiency setting) down to around 82-83% and then my readings on the Ecometer and my real world readings started to match more closely. I have been contemplating getting a Scanguage II because I would like to have other engine readings available and I am curious whether or not it has a setting for engine efficiency? Are those who's Scanguage II tell them they are getting 50+ mpg getting that same reading when calculating mpg at the pump after a fill up?
Hi Jay,
I logged most of my driving for over a year now. I tested the car at different constant speeds at long distances to improve accuracy. I can share with you some data if you help me figure out a good formula for figuring out MPG from it.
I should have probably added that readings were taken 3 times a second over OBDII interface on 3 to 5 (depending on period) parameters for extended periods of time including from a fillup to the fillup (hours of data). Let me know if you are interested to take a look at it.

I have a Scanguage II and have been using it in my 2008 Cabriolet for two years.   I have the "current" MPG and Trip MPG displayed full time.  Being a systems engineer and having the same commute for those two years; I made an informal study.

 

One has to remember that the OBD port only puts out data at 3hz...which is not bad.  The thing to remember is that it is unclear how Scan Gauge (or other add-ons) filter that data.  There is a definite lag in the display (it certainly doesn't display at 3hZ.  So you have to be careful in interpreting the data.  I found the Average Trip calculation to be a bit more helpful for long term analysis.

 

What I did find is that hills have a more dramatic impact on MPG that one might think.  I live on East Hill in Kent Washington and it's altitude is about 600 feet.  My work was in the valley which is -10.  What I did is modify my routes to better understand the impact.  I was surprised.  Since I also have a Garmin which can display altitude, I was able to monitor the altitude changes better.  There was a surprising difference.  One route stayed at sea level until I had to make the 600 foot climb to my house.  Another had several altitude changes.  The difference was up to 4-6 MPG. Note: the impact was due to the extra power needed to make the climb and probably had nothing to do with air pressure.

 

Dave

Even minor altitude changes impact mileage, especially if you are not watching the shifting.

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