FIRST LONG TRIP

[BIG ROCCO]

Went from Phoenix to Las Vegas and back this past weekend - about 600 miles round trip.  Dash readout was 43.6 MPG...calculated (miles driven/gallons used) was 41.5 MPG.  AC was off for 80% of the miles.  65-70 MPH mostly.  Car total mileage started out at ~2,700 miles - ended up at ~3,300 miles.  No hypermiling - no pulse, no glide, just drove it.  Lots of fairly flat terrain, but also some long (2 to 5 miles), steep, up and down grades.  Used cruise control on the flats - set to ~69 MPH.  Used the gas pedal on the steep hills, so picked up some speed on the downslopes and gave up some speed on the upslopes.

 

So, why the difference between dash readout and calculated MPG?  I never calculated it on the C-Max before, but friend with a C-Max told me the dash readout is always better than what he calculates.  Is the dash readout a lie?  Are the gas pumps wrong?  When I last did this trip in my 2012 LaCrosse with e-Assist, the dash readout and calculated MPG were about the same (34 MPG).

 

BTW, I felt very comfortable during the 5 hour trip in each direction, and would not hesitate to take the CM on even a longer trip.  My wife, on the other hand, wants to take the Buick next time - she said it's more luxurious and comfortable...so I guess you know which car we're taking next time.  That's OK - I mostly wanted to drive the CM just to put the miles on it, since it's really the wife's car and she obviously doesn't really drive much.  I figure the savings in gas C-Max vs. LaCrosse was about 4 gallons = ~$12.00 

[DaveofDurham]

Take a look at the "C-max MPG not calculated correctly" thread for a recent and ongoing discussion of trip odometer reported gallons used vs pump reported gallons added.

 

My difference over 18000+ miles and 40+ fill-ups is 4.7% (pump gallons greater than trip odometer gallons).  This is just about the difference you have on your 600 mile trip.

[mrobinso8]

Dash readout a lie.  My previous Fusion and now my C-Max and Fusion Hybrid always show 2 mpg better on car's computer than computed manually.

[ptjones]

I also agree with that although Pure GAS is pretty close.

 

Paul

[Jmonty]

That's great!

[DaveofDurham]

I also agree with that although Pure GAS is pretty close.

 

Paul

 

Paul -

 

Are you saying that when you run your car with pure gas (no ethanol) that you get better agreement between the trip odometer's report of gallons used and the gas pump's report of gallons pumped than when you run your car with a gas/ethanol blend?

 

If so, how close is the agreement when you run with pure gas and why do you think there is a difference in the spread when you run with pure gas vs. when you run with a gas/ethanol blend?

[BIG ROCCO]

Thanks for the replies.  It actually never occurred to me that the dash readout would lie.  I always thought that would be more accurate than calculating, due to differences in how "full" the tank is when filled.  I will check the next few CM tanks and report what I find for trip computer/dash readout vs. calculated.  I'm going to do the same for my Lacrosse.  Let's see if this is a Ford thing, or a GM thing also.

[fotomoto]

 Let's see if this is a Ford thing, or a GM thing also.

 

My prius was know for being 3-5% off.  The ones in my Nissans (quest van and cube) were off too.   

[ptjones]

Paul -

 

Are you saying that when you run your car with pure gas (no ethanol) that you get better agreement between the trip odometer's report of gallons used and the gas pump's report of gallons pumped than when you run your car with a gas/ethanol blend?

 

If so, how close is the agreement when you run with pure gas and why do you think there is a difference in the spread when you run with pure gas vs. when you run with a gas/ethanol blend?

Pure Gas has more BTU's(more energy) better gas mileage. Ethanol has approx. 50% less power than gasoline. This works out to about 5-7% MPG with ethanol blended gas.

Paul

[DaveofDurham]

Pure Gas has more BTU's(more energy) better gas mileage. Ethanol has approx. 50% less power than gasoline. This works out to about 5-7% MPG with ethanol blended gas.

Paul

 

 

I know about the BTU difference between gasoline and ethanol, and how it results in reduced MPG for ethanol blended gas compared to pure gas.

 

I thought you were saying that with pure gas you have seen better agreement between the trip odometer's report of gallons used and the gas pump's report of gallons pumped than you do when you run your car with a gas/ethanol blend.  Did I misinterpret your post (#4 in this thread)?

Edited November 13, 2013 by DaveofDurham

[ptjones]

I know about the BTU difference between gasoline and ethanol, and how it results in reduced MPG for ethanol blended gas compared to pure gas.

 

I thought you were saying that with pure gas you have seen better agreement between the trip odometer's report of gallons used and the gas pump's report of gallons pumped than you do when you run your car with a gas/ethanol blend.  Did I misinterpret your post (#4 in this thread)?

You thought right, Pure Gas agrees very closely with Smart Gauge.

 

Paul

[DaveofDurham]

You thought right, Pure Gas agrees very closely with Smart Gauge.

 

Paul

 

Do you know why there is better agreement between the gauge and the pump for pure gas than for an ethanol blend?

 

One factor could be the difference in specific gravity between gasoline and gas/ethanol blend - if the way the car estimates fuel usage is to somehow measure the mass used and convert the mass to volume using the density of gasoline (thereby underestimating gas/ethanol blend use since the blend is denser than gasoline).  Ethanol is denser than gasoline, 790 grams per liter for ethanol versus 730 (on average) for gasoline but that alone would not explain the discrepancy between the gauge and the pump for a 90/10 or 85/15 gas/ethanol blend.  [see graph on page 7 of document at

http://www.txideafarm.com/ethanol_fuel_properties_and_data.pdf ]

[marshtex2]

Although this thread started about a long trip it has gotten into a lot about looking at mpg so I'm posting the info below.  Where is a better place?

 

Now with 5,100 miles on my C-Max and the 10th fill-up I can report

that the average of the hand calculated mpg for each fill (416 to 575

odometer miles each) is 42.7 mpg.  For five of those fill-ups I hsd a

corresponding C-Max rating for each tank full.  For those five the hand

calculated average was 42.8 mpg and the C-Max rated average was 45.0.

The two most recent fills got 43.6 and 43.7 mpg by hand calculation

with C-Max showing 46.5 and 45.8, respectively.  On one of those fill-ups

I had odometer miles and gps miles (a little higher) and got 41.2 mpg

using odometer miles and 41.8 mpg using gps miles and C-Max showed 42.3. 

Included is a 1,400 mile trip (through Phoenix & Vegas) and overall only a

very little hypermile effort.  So there.  C-Max has always showed higher mpg than actual.

Still a great little car.

[Noah Harbinger]

Just had my first long drive as well, over Veterans' Day weekend. With about 5k miles on the odometer, I did a San Diego to San Francisco run. The hybrid is fantastic in LA traffic... terrible in the Central Valley.

 

First I should say that I still have not done the PCM update. What am I waiting for already? :-o

 

But with cruise set at 74MPH (yeah, sorry, it's slow - I don't like to go more than 5 over...) I was getting about 33-34MPG on the northbound direction. That is pretty darn terrible, in my opinion. The aerodynamics of this vehicle are just atrocious for faster driving.

 

After that I slowed to 70MPH, and was getting 38MPG. Southbound, again at 70MPH, I was getting about 42MPG. That difference is not unusual given the prevailing winds along the drive. 

 

Fuel economy in SF itself, I was running about 35MPH, despite staying with a friend living in a very hilly part of the city. The thing is a charming goat of a hill climber. 

 

Once I get the update, I'll have to do the trip again :)

 

MFT crashed on me once - had to stop, turn off the car, and turn it on/off repeatedly to convince it to reboot. A short drive in the city is tolerable but I ain't driving 6 hours without music. 

[ptjones]

Do you know why there is better agreement between the gauge and the pump for pure gas than for an ethanol blend?

 

One factor could be the difference in specific gravity between gasoline and gas/ethanol blend - if the way the car estimates fuel usage is to somehow measure the mass used and convert the mass to volume using the density of gasoline (thereby underestimating gas/ethanol blend use since the blend is denser than gasoline).  Ethanol is denser than gasoline, 790 grams per liter for ethanol versus 730 (on average) for gasoline but that alone would not explain the discrepancy between the gauge and the pump for a 90/10 or 85/15 gas/ethanol blend.  [see graph on page 7 of document at

http://www.txideafarm.com/ethanol_fuel_properties_and_data.pdf ]

I thought the ICE measure gas by volume not density? On my record run of 909mi and 13.9gal of Pure Gas vs Smart Gauge got 13.77gal. ,real close. With Reg I'm usually close to a gal difference. I do a lot of cross country driving and not all gas is created equal by my experience.

 

Paul

[BIG ROCCO]

Yes - that is fine - the subject line is First Long Trip.  The messages I wanted to convey were:

 

1.  The car is very capable and comfortable for a 5 hour trip

 

2.  The MPG for the trip and under what conditions

 

3.  The calculated MPG was less than the dash display.  Also, wondered if that is typical and if so, which is correct.

 

I think the answer to #3 is that it is not uncommon and I think the implication is that the calculated # is closer to the truth than the dash display.  I'm going to calculate the next few tankfuls and will report back on the outcome vs. dash display.

 

 

 

 

 

 

Although this thread started about a long trip it has gotten into a lot about looking at mpg so I'm posting the info below.  Where is a better place?

 

Now with 5,100 miles on my C-Max and the 10th fill-up I can report

that the average of the hand calculated mpg for each fill (416 to 575

odometer miles each) is 42.7 mpg.  For five of those fill-ups I hsd a

corresponding C-Max rating for each tank full.  For those five the hand

calculated average was 42.8 mpg and the C-Max rated average was 45.0.

The two most recent fills got 43.6 and 43.7 mpg by hand calculation

with C-Max showing 46.5 and 45.8, respectively.  On one of those fill-ups

I had odometer miles and gps miles (a little higher) and got 41.2 mpg

using odometer miles and 41.8 mpg using gps miles and C-Max showed 42.3. 

Included is a 1,400 mile trip (through Phoenix & Vegas) and overall only a

very little hypermile effort.  So there.  C-Max has always showed higher mpg than actual.

Still a great little car.