Check the oil level every time you fill up with fuel. You’ll find that every 3rd fill-up or so that it is necessary to add about 1/2 a quart of oil. THIS IS NORMAL. The rotary engine utilizes a metering system that draws a small amount of oil out of the oil pan and then feeds it into the engine with the air/fuel mixture to lubricate the apex seals. This oil is not retrieved but is burned with the air/fuel mix and then expelled out the exhaust.
However, just because the oil is replenished in this manner does not mean that you can get away with never changing the oil. In fact, it is wise to change the oil and oil filter every 3000 to 5000 miles (5000 to 8000 km) at the very least. Spring for the extra couple of bucks for a decent oil filter too. Purolator, AC Delco and Wix are good filters. The cheaper ones by Fram and Champion will usually do the job, but have been known to fail and allow bits of cardboard and glue to float around in engines and plug vital oil passages. Engines have failed because of this. True, the odds of you getting one that’s this bad are less than one in 20 but why chance it?
Oil grade and type:
Mazda’s owners’ manual recommends 20W50 non-synthetic multigrade, but unless you live in an area where the outside air temps rarely drop below 70F it’s best to use 10W30. If you live in places where the winter temps go below 0F you may want to go with 5W30 during those months.
There is an ongoing debate over whether synthetic oil should or should not be used in a rotary engine. One side of the argument says that synthetic doesn’t burn as clean when ingested by the engine via the oil metering system and should therefore never be used, while the other side claims that newer synthetics are ok and provide better protection. If you are running pre-mix (pre-mix = small amount of 2-cycle oil mixed with fuel, accompanied by removing the metering system) this argument becomes a moot point since the apex seals are no longer being lubed by engine oil from the pan. Otherwise, the non-synthetic engine oil does an excellent job and costs about 1/3rd as much as synthetic. That’s what I use.
Low-cost Engine Longevity
I know I lost a few of you with the preceeding paragraph on pre-mixing oil with the fuel. First, a little history:
When Mazda designed their version of the rotary engine they knew that the best oil for lubricating the apex seals (metal seals on the apexes of each rotor that do the same job in a rotary as piston rings do in piston engines) is 2-cycle oil. It burns cleaner leaving far fewer deposits behind to clog up seals and cause pre-ignition. But the rest of the engine still needs conventional 4-cycle oil to reduce friction, lube bearings and draw away heat from the center of the engine.
The problem is that Mazda also knew that telling new owners that their new Mazda required 2-cycle oil to be added to a separate reservior would scare customers away. After all, everyone “knew” that “2-cycle engines weren’t very durable, and if this new-fangled engine was a 2-cycle it probably wouldn’t last.” The knowledge that many owners who couldn’t be bothered to top up this reservior and would therefore destroy their engines in short order from lack of proper maintenance didn’t set very well with the folks at Mazda either. So they compromised. Instead of a separate reservior for 2-cycle oil to feed the apex seals, Mazda designed an oil metering pump that supplies engine oil to the apex seals in the manner described above. This oil doesn’t burn as clean and actually keeps the engine from lasting as long as it otherwise would, but it is still good for a respectable 200,000+ miles (300,000 km) if properly maintained.
But back to the pre-mix option: The racing community has been going this route since the early ’70s, when Mazda rotary-powered cars were first exported from Japan to the rest of the world. About 1/2 cup of 2-cycle oil is poured into the fuel tank when near empty and then the tank is filled with fuel, creating a thorough mix. The metering pump and delivery lines are discarded and a block-off plate is installed where the pump used to mount on the front lower right corner of the engine. This is simple and it works.
Another option is to install a metering pump adapter that utilizes a separate reservior and the stock metering pump. This adapter acts as a block-off plate to block oil flow from the oil pan while drawing in 2-cycle oil from a separate reservior and using the stock metering system to deliver it to the intakes.