Oil Temp never gets in the Green

Thanks Roger, the problem I have is that I have been told by rotax distributors that thermostats should not be used on their engines. This makes me hesitant to put one on if they have some good reason that I don't know about. Why don't they give a reason? Just saying "don't use them" leaves me hanging. 

Follow up question.  From the folks that use foil tape. Do you use the regular or high temp. The high temp stuff in the HVAC section at Lowes look like it is semi permenant.

The hardware stores usually have two types of Aluminun tape. A really thick kind and a thinner type that has a paper backing you peal off the stick it in place. Use the thinner one. It's 2" wide andplace it all the way across the radiator / cooler. Don't use Duct tape or Gorilla tape. Those two will leave a sticky residue all over.  The Aluminun tape is easy to apply and remove and it's cheap to use. I've been using it for 25 years. Used it on my Flight Drsign CTSW for 1500 hours. I know many people who use it and it works fine.

Here's what I did, see image attached. The tape itself wouldn't stick to the radiator, so I cut out a piece of cardboard and used the aluminum tape to stick it to the fuselage. In combination with my cowl flap I am now able to control the temps rather well. Getting over 100°C for water evaporation still requires some work though, I need to climb at a steep angle for a few minutes for the oil to reach 100+, so flying on days with a low ceiling makes that a bit difficult. After that, at temps around freezing, I can manage to keep the oil at around 85-95 degrees, depending on power setting.

Thanks Pascal.  I tried the Metal Tape and it seems to work for me, but I'll bet it's lots colder in your neck of the woods.