Notes on the Big 3-0-0 (k):
- At about 175,000 miles, we were hit with the dreaded "broken crank" problem which can occur on all 1990 and some early 1991 Miatas. The 175,000 mile mark is quite late for the problem; all other instances that we know of occurred much earlier in the engine life. In our case, the best fix was a new engine installed by a dealer with a very good SOCALM discount. A new clutch was installed at the same time. The second engine has been fed Mobil 1 10w-30, with oil and filter changes every 3,000 to 4,000 miles. We do it ourselves.
- The brakes last an incredibly long time. Pad changes were very infrequent. The original rotors lasted until about 235,000 miles, with the fronts having been turned twice and the rears once. The brake hydraulic system has not needed service other than being flushed two or three times.
- The first catalytic convertor lasted almost 200,000 miles. A second one only lasted about 20,000 miles but this was because a dirty throttle body caused an excessively rich fuel mixture, destroying the convertor. The exhaust system has otherwise not needed repair.
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There have been four timing belt changes on the two engines. The first was done by the dealer, the others were DIY projects. While not for the "mechanically challenged", they are possible to successfully undertake for an amateur mechanic.
As the miles added up, a number of smaller things broke. These included the
- Radiator (twice; the first replacement was used)
- Alternator
- Speedometer cable
- Rear hub bearing
- Front hood cable release
- Clutch slave cylinder (rebuilt twice)
- Clutch master cylinder (replaced once)
- Airflow metering sensor
- Starter motor
Fuel Mileage
We have kept a diary (if you could call an Excel spreadsheet a diary!) of the fuel consumption.
- Overall fuel mileage: 29.6025 miles per gallon
- Average fuel cost: $1.572 per gallon
- The highest fuel cost was $3.699 per gallon on 5/7/2006.
- The average fill-up was 8.958 gallons.
- The largest fill-up quantity was 10.500 gallons on 3/6/2004.
- The average fill-up cost was $14.188.
- The highest fill-up cost was $35.48 on 7/17/2006
- The lowest fill-up cost was $4.69 on 9/11/94
- The total number of fill-ups: 1,136.
- The total number of gallons: 10,176.493.
- The total fuel cost is $16,117.70.
It's worth noting that the speedometer cable was broken for about a week. We estimate (based on the fuel consumed during that time) that it was broken for 817 miles. This means that the car actually passed the 300,000 mile mark a few weeks earlier. The indicated mileage was the basis for this celebration. The fuel logs reflect the corrected mileage. Also we installed a Jackson Racing Cold Air Induction system on 6/14/1998 and bumped the timing to 10° and started using 92 / 91 octane at that point.
The MPG was consistent with several events causing a drop in fuel efficiency. When the first catalytic convertor gave up the MPG dropped to 22.4. Various track days at Willow Springs caused 21 to 25 MPG ratings. Changing the timing belt, which also accompanied a spark plug change, did not result in a noticeable difference
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