There is running cool and there is running
too cool, for both water temp and oil temp. When you say it's running cooler than your last GTT, I'm guessing you're looking at the water temp gauge in the dash, which obviously wont tell you the temp of the oil...
Read this before going any further:
http://www.tuneruniversity.com/blog/...l-temperature/
The car will run best if it's allowed to get into the temperature range Renault intended. In respect to your oil temp, look at the OE oil cooler; a thin pipe down the side of the radiator. Now look at your oil radiator set-up. You're cooling your oil much more. Without an oil temp gauge or a thermostat in the sandwich plate, how do you know it's
ever reaching the intended operating temperature? That's why I said it's not ideal to run without one.
Like you say, you might be fine. It has been to this point. It's up to you whether you're bothered enough to be certain.