Accuracy of Tank Avg reading??
 

I recently finisheda 7 day family road trip that totaled over 1600 miles. The bulk of these miles were pure highway miles of 350-500 (6-12 hour stretchs of time) miles at a time. I was curious to see how efficient my gas mileage could be. To be as efficient as possible, I used:
* regular gasoline
* cruise control
* tried to average 55-65 mph.
*used the AC sparingly, I had the thermostat set 75-77 degees when necessary

Even with these settings, I was expecting, at best, 35mpg. So imagine my delight/shock when I saw my "Tank Avg" climb to 41.5 MPG, on my 4-cyl 2007 Camry XLE. I thought this was a fluke. So I was shocked to get greater than 39 mpg during a number of other intervals during this trip. I was ecstatic to get these results but now I'm wondering how accurate these readings really are.

I noticed that my MPG really start to increase at the sweet spot of 45 MPH, during a stretch of highway construction miles. In this construction zone, I traveled for about 5-10 minutes at 45 MPH and I saw my MPG quickly climb to nearly 42 MPG. In fact, my results indicate the 45-55 MPH is best to acheive peak MPG. I think Consumer Reports recently reported this as well.

So how accurate is Tank Avg reading? Is it reliable? Do the rest of you get highway MPG like this?

Thanks.

RE: Accuracy of Tank Avg reading??
 

Looks like my MPG weren't a fluke:
http://www.consumerreports.org/cro/c...-406/index.htm

Consumer Reports confirms my finds. I'm happy.

RE: Accuracy of Tank Avg reading??
 

Actually, I've got a 1998 4-cyl that obtains very similar mileages at similar speeds. You are right in your definition of the sweet spot being 45-55 mph. This is true on most vehicles, including my 2001 Sienna which achieves its greatest fuel efficiency at 45-48 mph, likely because of its taller profile leading to greater wind resistance.

RE: Accuracy of Tank Avg reading??
 

Regarding accuracy of your onboard computer...they are quite accurate.

My dad bought a 2007 Camry hybrid last summer. I have personally driven it on several occasions, including a 2000 mile road trip (round-trip total). The onboard computer estimates were allwithin 2/10 of a mpg every time we manually calculated mpg.

RE: Accuracy of Tank Avg reading??
 

I'm thinking to prove out the computer that you should do a tank to tank manual calculation for several tanks. The computer also puts the coasting mileage in there, so I don't know how it calculates the "average".

RE: Accuracy of Tank Avg reading??
 

Sweet spots for a lot of cars is at 45-55 due to good crusing speed and decent mix of wind resistance.
Toyota's have traditionally had more exaggerated MPG readings (giving you 1 to 2 more MPG than you actually are getting), but they're generally pretty on the dot.

Now if we could all drive 45, windows up, no fan/ac or other electronics and lighten the car, super inflate the tires, im surea bunch of us could get 30+ mpg. hehe.

RE: Accuracy of Tank Avg reading??
 

I should add while driving in an is250, it's sweet spot was about 50mph. The live mpg meter was reading 40. haha.

Gas mileage computer accuracy
 

I currently drive a 2012 SE 2.5 L Camry. Recently, I drove about 250 miles at close to 60 mph. The computer read out 39.9 mpg. It was climbing consistently, and I know would have done better with a few more miles driven. However, I checked it manually once before, and the computer was about 1-2 mpg higher than I calculated. I have owned a Chevrolet Malibu and a 2010 Camry, both with MPG computers. Each of them was 1-2 mpg over my calculations on a regular basis. I try to stop pumping gas when the pump shuts off automatically, so the fillings are relatively consistent. I discussed this and other factors with an on-line moderator at CR, and he discounted such things as temperature and how high the pump's pouring pressure was (differing pressures would make a difference in its automatic shut-off, and temperature would make a difference in fuel expansion, but he wouldn't agree that it was a factor). Nevertheless, anything causing us to be aware of our driving habits in relationship to the cost of driving is a good thing. Perfect accuracy is not necessary if we are caused to do the right thing by the info we get.

I traded a 2011 Hyundai Sonata LTD 2.4 L for this car. According to the computer, it got 41.2 and 42.1 mpg on several occasions. I think that my Camry will at least equal that. Some trade offs here due to amenities galore in the Hyundai, but I'm happy, and enjoy being back in a Camry.

By the way, it seems to me that the digital and the analogue needle meters are redundant. I would like for the analogue to suggest the current at-the-moment economy of my driving rather than the average mpg.