What Kind of Gas Mileage Does a Mazda Miata Get?

.   .   .   The Ultimate Answer!

1990 Mazda Miata

(Here is the last word on the subject)

Call us anal. We consider it a compliment!

Throughout the entire twelve, year eight month, 250,152 mile life of our 1990 Mazda Miata, we have recorded every fuel fillup. The first was a 6.871 gallons on 8/11/90, and the last, as of 4/16/2003, was 9.409 gallons. All the data was then put into the WebCars! Fuel Economy Calculator, a web based program designed to track such things.

The Results:
  • Overall Fuel Mileage: 29.8473 miles per gallon
  • Number of fillups: 946
  • Total Number of Gallons: 8381.052
  • Total fuel cost: $11,617.30
  • Average fuel cost: $1.386 per gallon
Some Notes
Every fillup was self-serve and was concluded when the automatic shutoff on the pump kicked in; at no time did we top it off to get an even $$ amount. Even so, the fillups were not consistent, as the mileage for the individual fillups were all over the map. One might yield 28 MPG and the next 32 MPG. The moral of the story: Calculating fuel economy should be done over a number of fillups. Using just one will not give an accurate reading. Our guess is that inconsitencies with the automatic shutoff is the source of the variations.

The EPA rating for the 1990 Miata was 30 MPG Highway and 25 MPG City. In our case those statistics were close, but a little conservative.

In the logs we recorded anything that might affect the mileage. All tune-ups were noted for example. A couple of times the spark plug wires pooped out. At 166,233 miles a Jackson Racing Cold Air Induction kit was installed, at which time the timing was reset to 10° and we started to use 92 octane fuel. Strangely enough, these items did not make a noticeable difference.

One item that showed up big time on the results was the catalytic convertor going south. It went at about 205,000 miles, and was the original catalytic, so it's not like we have a complaint! There was plenty of warning in the form of a distinct rattle. On our annual pilgrimage to Monterey CA for the "Car Weekend" (as it has come to be known), it became a problem, as power was significantly down and the engine was running hot. An emergency repair was performed on Sunday at Midas Muffler of Seaside CA. Before that the mileage had been dropping: 28.401 MPG, 26.705 MPG, 26.459 MPG, and then 22.453 MPG. After the repairs, it shot up to 27.005 MPG.

We were hit with the infamous "Bad Crank" problem, which has affected a number of 1990 and early 1991 Miatas. It occurred at about 177,000 miles, and we elected to replace the engine with a new one from Mazda. Separating the new/old engine data produced interesting results. The original motor produced 30.2546 MPG. Its replacement, in service for approximately 30,000 miles, has offered only 27.9738 MPG.

You can view the entire log; however unless you have a high speed connection (DSL, cable modem or you do your web surfing at work) we do not recommend it as the file is 328k. If you are using a conventional modem a smaller page with only the last 50 fillups is a wiser choice. Pages with the data before and after the engine was replaced are also available. There you will also find all sorts of other data, as only a computer would (or could) generate.

The same program used to generate the data is available online to anyone similarly inclined to monitor their gas mileage. You can go to www.web-cars.com/math/fuel_register.html and set up an account. Be aware however that this is beta software. That's computer lingo for "We're not really confident of this, so use at your own risk." Visit the WebCars! Fuel Mileage Calculator Instructions page for more information.


(Your Mileage May Vary)

It is well known that driving style has a significant affect on gas mileage. This Miata is 70% driven by Francie Pollock and 30% by her husband Paul. Francie is driver-ed smooth while Paul seems to be constantly trying to qualify for the Indy 500. No attempt was made to log who drove when. The car has been to several driving schools and autocrosses, which is extremely hard use. One driving school, at Willow Springs International Raceway, resulted in 21.044 MPG.

Comments? Suggestions? Let us know!
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