We are midway through the summer and the RX8 mileage continues to be about the same.  The last tank covered 247 miles using about 13.9 gallons of premium gas.

Driving was a mix of city and highway driving with most of the driving done on the surface streets near my home and work.  I am now using the entire RPM range of the RX8, redlining the rotary every trip.  The new motor feels much more powerful.  However, I still experience dips in power at 4k and 7k.  It would be nice if this could be smoothed out.

Fuel Economy Results

• Total miles driven: 247.3
• Total gallons used: 13.897
• Fuel Mileage:17.8 MPG
• Fuel Cost: 53.14
• Cost per mile: 21 cents per mile
• Cost per gallon $3.82 (93 Octane)

It has been a little while since I updated my fuel mileage thread.  I decided to do a recap of my fuel economy so far.  It seems that since the new motor, the overall mileage has slightly improved.  However, the improvement is not significant.  The last half tank was approaching 20MPG was a highway only burst with an average speed of 80-90 MPH with constant acceleration and braking.  I consider this quite good given the driving style.  The previous half tank was 90% city driving.  Again at 15.2 MPG it was quite terrible.

Since the beginning of my record keeping, my average fuel mileage is 16.8 MPG with a high of 20.1 and a low of 14.7. I have yet to reach the HWY MPG of 24 stated by the EPA.  Maybe next time. Below are some detailed stats.

Click on spread sheet to enlarge

My recent tank is not so great.  Except for the last 50 miles, it was all city driving.  Below are the results.  It is amazing how bad it can be.  Not the absolute worst, but not that far off.

Next week I am organizing a Dyno Day.  So I am sure the mileage will be low.

Fuel Economy Results

• Total miles driven: 214.1
• Total gallons used: 14.142
• Fuel Milage: 15.14
• Fuel Cost: 57.40
• Cost per mile: 26.8 cents per mile

I just got back from a trip to Indianapolis. It is about 110 miles one way. I as able to eek out an surprising 274.5 miles out of the RX8 tank. With over 70% of highway driving, the RX8 finally exceeded 20 MPG. (Just barely)

The outbound trip was in total darkness with an average a significant amount of cruising at 79 mph. The return trip was as a lesser 75 mph. Considering my average “in town” fuel economy is around 14.5 MPG, I think it is possible to increase the highway mileage to I think it is possible to get up to 22.5 MPG. Driving style and weather conditions. Below are the details.

Fuel Economy Results

• Total miles driven: 274.5
• Total gallons used: 13.643
• Fuel Milage:20.13
• Fuel Cost: 54.56
• Cost per mile: 19.9 cents per mile

I recently found out that some people do not know how to calculate fuel economy. I have to admit, I was stunned. I also realized that some people are missing this critical tool they can use to monitor the status of their vehicle. Below is a quick tutorial on how I measure fuel economy. This is relatively easy to do as long as you follow the basic principles I have listed.

Measuring MPG (Miles per gallon)

1. Fill up your tank with gas. Let the pump stop on its own. (Letting the pump stop on its own increases the accuracy of your calculations)
2. Reset your trip odometer. If you do not have a trip odometer, write down your regular odometer mileage.
3. Drive the car. For the most consistent average, try get as close as possible to “E” or empty. (This last part is not necessary but does help in better averaging.)
4. Go back to the same gas station (Same pump if possible) and fill up. Let the pump stop on its own. (Letting the pump stop on its own increases the accuracy of your calculations)
5. Document how many miles you have driven.
6. Document how many gallons of fuel you needed to fill up.
7. Divide the number of miles driven by the number of gallons required to full up the tank. This is your fuel mileage.

First Results

• Miles Driven: 215.6
• Gallons used: 13.444
• MPG: 215.6/13.444 = 16.04 MPG
• Total Cost: $53.36 Ouch ($3.969 per gallon for 93 octane)
  
• Cost per mile: 53.36/215.6 = $0.25/Mile
  

Notes:

This mileage was a combination of 50% city and highway driving. As always, it was spirited. My next trip is to Indiana this weekend. It will be interesting to see how the mileage changes with 90%+ highway driving.

According to the 2003 Bureau of Transportation Statistics (BTS) Omnibus Household Survey, the average commute to work is 26 minute, 15 mile one-way trip to work. Based on my figures above, the an average RX8 commuter will spend $7.50 a day, 37.50 a week or $1875 a year (assuming two weeks vacation) in fuel costs alone.

An increase to 20 MPG would result in a annual cost savings of $371.25. Increasing mileage to 25 MPG would reduce fuel costs by $672. Of course, we did not buy a sports car for the fuel economy.