Northstar Engines and System Technical Discussion Discussion, 160* Thermostat? in Cadillac Engine Technical Discussion; I put 160* thermostats in my other cars with great results.
I've heard the N* is supposed to run hot. ...
Your OEM thermostat is set to begin opening at 188 and fully open at 206. The engine sensors are all calibrated to "assume" a running temperature of about 195-200 degrees. Your cooling fans run in slow whenever any A/C function is set, and if the A/C is turned OFF fans go to SLOW at 224 degrees and FAST at 236 degrees.
A 160 degree thermostat forces the sensors to compensate for a "low temperature" engine fault which gives longer cat lightoff times, slightly richer fuel mixtures and cool oil (which is detrimental to efficiency and oil cleansing through evaporation of contaminants/acids).
The Northstar does not run hot. It runs right in the design temperature band, and if we had better coolants, engines would benefit from running up in the 225-240 degree range due to higher efficiency.
Click the pic to enlarge and see where the engine is running with the gauge at 12:00, its normal reading. In heavy traffic a Northstar FWD will easily go to 225 and back down as the fans cycle.