High oil temp with Franz oil thermostat

It sounds like the thermostat is not Closing and is continuously bypassing the Cooler.
Remove the Thermal Cartridge and place it in a pan of water on a stove.
Does it close as expected when you heat up the water?

Any chance the Flow direction is reversed?
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Roberto,
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While you're checking the thermostat make sure no oil hose makes such a sharp turn like a 180 degrees where the hose at the bend is collapsing and slowing the oil flow. I have seen many like this and I put a spring inside to keep the hose fulling open. It usually drops the higher temps by around 20F. I'm not bending the hose in the picture. It's the way I found it.

Roger's idea of a kinked hose is a good call.
Are you also seeing unusually low Oil pressure? (<2 bar?)

I am not sure if there is a wrong way to install the Thermostat.
Most installations appear to have the flow coming IN the Large Diameter end and OUT the smaller pipe end.
Is there any chance that the Thermal Element is mis-installed or missing?

Here is a hose that will not collapse at 266 deg under a full vacuum while tied in a knot, it is teflon and should last the life of the aircraft.

https://www.pegasusautoracing.com/group.asp?GroupID=PLUMANFLEX

I take a picture of the lower part of the thermostat, the tube is bend 180° do you think could be a problem? the pressure still in the green arc.