That's not quite true. You'll get blowby through the side seals which ends up bypassing the oil seals and into the "crankcase" via the center hole in the irons through which the eccentric shaft passes. Just like a piston engine the rotary has a PCV system to vent the vapours. Though Mazda's system is a bit more well designed in that it sucks fresh air deep into the center of the engine and then draws it off from the oil filler neck to really purge the engine. High power turbo engines tend to have a problem with blowby as the stock system cannot keep up when there is no vacuum present in the intake tract.Dgate said:The sump in a rotary is closed off from the engine workings and is never contaminated with blow by or contact with the combustion process.
They most certainly do need an oil change and the schedule very clear in the owners manual like any other vehicle. Especially if the car is turbocharged.Thats why they never need an oil change only topping up as the oil is metered into the intake with the fuel and is consumed.