Engine running hot

caltrip

My 308 Hornet wants to run hot. This problem just started suddenly.  160 thermostat and car runs at 190. New thermostat, radiator overflow tank loses water. Engine sounds ok. Problem happened suddenly. Prior to problem car ran at 160-175. No noticeable external leaks. Coolant tests negative for combustion gases. Any suggestions?

Ol racer

First suggest Double Check the temperature using a cheap Cooking Thermometer to validate your reading. Sometimes a radiator will throw out a little coolant if filled right to top. If Thermometer verifies actually running warmer, there are things to check that we on this Forum can suggest.

Jon B

Thermostat, even if new, might be defective.  This happened to me suddenly, in my Terraplane several decades ago.  One minute...ran cool.  Suddenly the needle went all the way to the top and steam poured out from under the hood.  When it cooled down I removed and examined the thermostat.  It was "stuck shut".  I removed it from the car, and the car ran fine.  I replaced it as soon as I got home from the trip.