Rotax four stroke aircraft engines have proven themselves as reliable pieces of machinery. They can be bought as experimental (UL) or certified (A and F) engine and there are four main models (injected too) to date. The original engine is the 80 hp 912, from which the 100 hp 912S was developed and Rotax also has a 115 hp turbocharged 914 engine. In 2015 Rotax announced the 135 hp fuel injected turbocharged 915iS.
Field experience has led to the conclusion that without any temperature control the oil of the Rotax engine sometimes does not get to specifications in certain circumstances.
This service letter recommends a thermostat to be used in these engines.
SL-912-011 SL-914-009, Oil Thermostat
Excerpt from the document:
Field reports say that different aircraft with ROTAX engines type 912 and 914 have oil temperatures too low during engine installation because of unsatisfactory installation.
In my opinion Rotax has build an engine without any temperature control in the coolant or oil system which is rather strange to say the least. Their engines operate from Canada into the tropics and did they really think that the OAT temperature did not have any influence at all? Anyway, install such a device and be done with it.
To continue reading see the pdf below: