Low Oil Temperature after decent and Burning Smell with Rotax 912uls

No idea about the burning smell but your oil temperatures are below Rotax advised minimum of 50C

I've also been having an issue with too-cold temps.  Takes several minutes to get up to 50C (120F) and even then it sometimes slightly dips down below that point in flight and certainly after landing.

I think my oil thermostat is simply not functioning.  I put covers over parts of the oil cooler and radiator and it doesn't seem to make much difference.  Personally, I think this is a flaw in the Rotax design.

I'm glad the weather is starting to warm up...

Sorry ! Cant help you, lack of experience - in my part of Australia, we think the one or two frosts we have per year is REALY COLD!

If you’re blanking off the oil cooler when you have a thermostat it would probably be safe to say that it’s not functioning correctly and probably stuck open. If’s it’s working properly then you shouldn’t be blanking off the cooler.