As others are telling you, remove the filter canister and clean it out, retorque the head, and install a t-stat. The purpose of the t-stat is to quickly get the engine to itís optimum operating temp and keep it there. Do use a thermostat. If you don't the engine heats unevenly, which means it wears unevenly. A cool-running engine does not heat the oil sufficiently and you will get sludge build-up in the pan as a result. Further, water will remain in the oil because the oil never gets hot enough to evaporate the water; that creates acids in the oil leading to bearing corrosion. N tractors came from the factory in 1939 with a 160-degree thermostat. Ford added t-stats to cars in 1933. If you want to use a 180* t-stat (which I use on all 4 of my 8N's) try A&I part # A-11C15, Gates 33108, Beck/Arnley part # 143-0024, Auto Zone part # 3518 or NAPA part number THM 184 for 180* in hose t-stats.
The car parts store folks are helpless w/o vehicle make/model/year info. Some can/will actually search on the number & cross reference, but more often than not, you will just get a dumb look. HINT: find a clerk near the age of your tractor..... ;) Try telling them that the t-stat is for your 1977 Renault R12 1.6L L4.
All of my 180* t-stats are A&I A-11C15's or AZ-3518's. They are a very tight fit in an N hose, but they will fit. I've never used the Gates, Beck/Arnley or NAPA t-stats so I can't help you w/ anything there but the part numbers.
All that being said.....if you do not consistently run the tractor to operating temp, you will get condensation & sludge as a result even w/ a t-stat installed.