Spark Plug Life Expectancy
   by Mark Schroeder
   mazrx7@onramp.net

   Driving style has everything to do with plug life. On the '86-'91 models, never exceed 20,000 miles on plugs ever. The center ceramic falls apart and guess where it goes. Engine failure. Big problem in '86 when Mazda used the SD series plugs. Anyone still using them or has any, throw them out. The do not have the electrodes that surround the center one, and when they crack, falls instantly into engine. The best plugs for the '79-'85 models is likely the B7ET ('79-'80) or BR8EQ-14 '81-'85. The '86-'91 models can use the '93-'95 BUR7(9)EQP plugs for increased durability.

   As far as when to replace: 15,000 miles is the average for a vehicle driven by grandma. If driven hard, expect 7,500-10,000 miles. For high boost situations, cut that in half. I run a high RPM ported engine, 2 MSD boxes, a rich intake mixture and lots of timing [advance], and replace my plugs with every oil change, about 1,500-2,000 miles. It's cheap insurance. Cap and rotor, and wires also wear lots with MSD or similar boxes. 5,000-7,500 miles is about all I would expect if driven hard. On race cars (ITA), plan on new plugs and cap/rotor every race weekend.

   Plugs are the closest thing to the engine and should not be treated lightly. Dealers usually charge too much for plugs (ex. $98.25 per set for '93 models). There are better sources for these plugs.

[Read what David Lane has to say about the importance of maintaining your rotary's spark plugs.]