For many years there has been much debate about whether synthetic oil should be used in Mazda rotary engines. The unique rotary or wankel engine has powered the Mazda RX-7 and later the RX-8 for a generation. The main concerns were seal compatibility and carbon deposit buildup. Modern synthetics are completely compatible with the seals and elastomers in rotary engines. This issue may or may not have been valid during the early days of synthetics, but today’s formulations have long laid that canard to rest.
As for the carbon concern, let’s quickly touch on the fashion in which engine oil is used to lubricate a rotary engine. A typical rotary engine has a three-lobed rotor that rotates inside an oval-shaped chamber to create combustion rather than reciprocating pistons. A metering pump injects a small amount of oil into the combustion chamber. A small portion of this oil is meant to burn by design and it must burn cleanly. The common concern was that synthetic oil did not burn cleanly enough and would therefore leave carbon deposits that would lead to poor performance and ultimately engine failure.
AMSOIL has recently published a Technical Service Bulletin addressing these questions. The TSB: Using AMSOIL in Mazda RENESIS Rotary Engines shows how AMSOIL synthetic engine oils actually burn at similar temperatures to competing conventional and synthetic oils. The bulletin charts the flash points of 13 different motor oils which could be used in the late model RENESIS engines. Another concern is that higher ash content oils can form more carbon deposits than lower ash content oils. Today’s conventional and synthetic 5W-20 or 0W-20 formulations (the weight Maxda recommends for RENESIS engines) have a reduced ash content. AMSOIL recommends AMSOIL 0W-20 Synthetic Motor Oil (ASM) and 5W-20 XL Synthetic Motor Oil (XLM) for the Mazda RENESIS engines. AMSOIL also recommends their motor oils in older Mazda rotary models.
Keep in mind that AMSOIL is very conservative when it comes to making product suggestions. If they have concerns about recommending a product for a particular application, they simply don’t until their Technical Department has completed exhaustive research. Check out our Online Application Guide for more details on your model. For more information on this engine concept, check out the Wikipedia article on Wankel or Rotary Engines.