Roger, Rob, Mike and all,
You have convinced me. After thinking about what all of you are saying, I do believe it is an unacceptable critical reduction in reliability to Rotax 912 aircraft engines to add (“currently available”) thermostats to either oil or coolant systems. The problem, as you put it, is that if the thermostats fail to send adequate hot liquid to a cooler, destructive high temperatures will occur.
I also want to thank everyone who is running thermostats for your responses as well. Very helpful.
Just for discussion:
Perhaps on the coolant side this might not do damage if quickly recognized and countered by reduction to very low power until an airport can be reached. I say this but I don’t know if this is the case, if that is what would happen, e.g. if the ThermoBob were to only route all coolant via the 3/8” bypass while blocking off the cooler. The resultant hot coolant might raise pressure enough to blow by the pressure cap even at low power settings until it becomes a case of no coolant, which Rotax seems able to handle even if it is not something we want to have happen.
But on the oil side, both Thermostasis and PermaCool continue to send some oil through the cooler in all configurations and temperatures (and failure modes). The questions here might be: is this enough cooling to proceed on reduced power (as with the loss of coolant) to an airport, and how quickly and how high would oil temperatures rise with 90% reduction of oil going through the heat exchanger?
Wouldn’t our engines benefit from truly reliable (or fail-safe – which needs to be defined based on our Rotax engine needs) thermostats. I do not know what is inside the Thermostasis, but I do know an automotive waxstat is inside the PermaCool as well as the Thermo-Bob. I suspect all coolant thermostats have a waxstats. I have not seen very many automotive thermostats fail, but my stock Permacool waxstat failed. Did I make this happen by placing the room temperature 170 degree waxstat directly into boiling water? My oil in summer will get hotter than 212, but it would do so more gradually than when I tossed that room temperature waxstat into the boiling water.
In absence of knowing if any ‘truly reliable (or fail-safe)’ thermostats exist, I think it is better to tape over heat exchangers. What I would like to know is what is happening inside the engine when running at too-cold take-off power or during sustained too-cold cruise – and this goes for both coolant and oil. I would also like to know how many people are running thermostats and what have been their experiences; how many have had failures and what happened.
In summary, after all the time I spent researching thermostats, and the money spent on parts and miscellaneous fittings and new hoses, as well as effort to cut into lines and neatly configure and locate automatic temperature controls on my Rotax (and being proud of the results), I am now concluding that I need to tear all that crap off and go to taping over heat exchangers. Oh well. What is safest = what is best.
Thanks for the help,
Dennis Urban
