Up date on my 97 C280

On a recent cold AM day ( 60*F ) the engine never got above 160. When temps rose to 80*F, engine temp was 200 ish and would rise to 220 at idle. If I brought engine speed to 1,200 RPM, temps would drop to 190 ish.

Pulled thermostat, found bridge was broken ( where the stem presses against ) the valve was off center allowing for maybe 20% coolant flow. More importantly, the bypass blocking disc was not shutting off the bypass and allowed most water to recirculate. Luckely, half of the bridge was still holding the stem off to the side, otherwise it would have snapped shut and overheated the motor quickly.

Bridge was cracked for a long time based on the brass being dull. It probably finally broke completely just after I started driving the car. ( it was sitting for a few years. ) Given air temps were low the problem was unnoticed. Changing the T stat as a precaution was on my rebuild list and just hadn't gotten that far. This is a perfect example of why I life parts when the get high hours rather than wait for them to fail.

Looking at engine temp through the HVAC on 97 system is easy and more accurate than a needle. Fan on, key in 2 run position, press and hold REST, wait for 01 and a number to flash back and forth. Use fan - + buttons to scroll through the values. Coolant temp is in the range of 05 or 06. There is a chart for the values on the net. ( heater core / evap temp / pressure, bat voltage, AC high pressure and lots of other stuff. )

Car runs at 195 / 7 when warmed up even in 92* weather, at 60 temps engine does not run below 188 and will creep to 195 after everything heat soaks.