oil purge with oil cooler thermostat question

I just did an oil system line change and an oil purge since all the oil was drained from all systems. I got to thinking that the oil thermostat bypasses the oil cooler and opens when the temperature reaches 120 or so F to open. If I did an oil purge with the engine cold, is air trapped behind the oil thermostat, in the oil radiator/cooler, and after it opens when temperature reaches 120 F or so flying, does this allow air to get into the oil system making the oil purge void? Although I have the 912iS this question should be applicable to ALL ROTAX engines with an oil thermostat.