Using stock Mazda coolant “O” rings and exceeding those temperatures would indeed compromise the “O” rings and you end up with coolant in your combustion chamber and/or combustion gases in your coolant galleys – I know - as it happened to me as well as others when first sorting out  my installation back over 10 years ago.

 

However, once we found and  substituted TES (Teflon Encapsulate Silicon) coolant  “O” rings with a much higher temperature rating, and Viton seals for the oil ring seals,  it became quickly apparent that a lot of the problem with elevated temperatures had been the “O” rings and somewhat  higher temperatures could now be sustained without any apparent damage or problems.  Not to say, higher temperatures are recommended, but many of us have found brief excursions above 200F do not cause any detectable problems.

 

 

My normal cruise coolant and oil temps are within 5F of each other and normally range from 160F to 185F at cruise depending on power levels and OAT.  So as a percentage of operating time, my temperature excursions are on the order of 1.6% of my total engine operating time.  On a hot 90+ day, I will exceed 200F during climbout until I hit 120 MPH IAS – usually a brief period of from 2-3 minutes before airflow catches up with heat being produced. 

 

Numerous rotary installations now fly with red lines above what would have been  prudent if using the older stock Mazda “O” rings.  I have over 8 years on my installation with TES “O” rings, Tracy Crook over 15 years the vast majority of it with the TES  “O” rings.  So until we get some aircraft with over 2000 hours on an engine (and set of TES O rings), we really won’t know whether these brief excursions are resulting in accumulated ill effects or not.  If it takes 2000 + hour to manifest itself – then I am not concerned.

 

There is no question that the rotary can not, for the reasons mentioned by several, with stand the temperature ranges of most piston engines – however, we are not quite as bound by earlier limits (at least for limited time periods) as we once were.  Thanks to sturdier seals.

 

We had 8 rotary powered aircraft at the Texas Rotary Round up and it would be interesting to know how many have exceeded 200F and any heat associated problems.  Although most have less than 500 hours, so not a true indication of what to expect one way or the other

 

Time changes, technology advances and improvements are found.

 

Ed