The Rotax 912iS engine has very detailed and specific design requirements regarding the installation on an airframe.
A huge amount of engineering effort was invested to assure the RV-12iS meets all of the installation requirements stipulated by Rotax, and then compliance of the installation was proven with detailed testing.
One of the tests required by Rotax is related to flow resistance within the oil cooler circuit. Testing showed that a thermostasis oil thermostat added enough flow resistance that the test requirements couldn't be met, regardless of the fitting and hose configuration.
Rotax has periodically updated the installation requirements for their engines over the years and this test was at some point added to the ULS engine installation manual as well. Anyone installing an oil thermostat should do these checks or ask the vendor that is providing the installation kit, if the can certify that the checks have been done (particularly if you engine is still under factory warranty).
One of the few differences in the core engine between the ULS and the iS is that the iS has a higher flow volume oil pump. All of this info should be taken into consideration when contemplating installation of an oil thermostat.
BTW, for reasons not entirely understood at this point, the iS version of the engine warms up during ground operations much faster than the ULS version does (even with the redesigned cowling and both heat exchangers located directly in the prop blast).
A huge amount of engineering effort was invested to assure the RV-12iS meets all of the installation requirements stipulated by Rotax, and then compliance of the installation was proven with detailed testing.
One of the tests required by Rotax is related to flow resistance within the oil cooler circuit. Testing showed that a thermostasis oil thermostat added enough flow resistance that the test requirements couldn't be met, regardless of the fitting and hose configuration.
Rotax has periodically updated the installation requirements for their engines over the years and this test was at some point added to the ULS engine installation manual as well. Anyone installing an oil thermostat should do these checks or ask the vendor that is providing the installation kit, if the can certify that the checks have been done (particularly if you engine is still under factory warranty).
One of the few differences in the core engine between the ULS and the iS is that the iS has a higher flow volume oil pump. All of this info should be taken into consideration when contemplating installation of an oil thermostat.
BTW, for reasons not entirely understood at this point, the iS version of the engine warms up during ground operations much faster than the ULS version does (even with the redesigned cowling and both heat exchangers located directly in the prop blast).