coolant thermostat question
 

My 190 is running hotter than normal. In day time running on the freeway with temps from 70's- to 80's the car is running at around 105C. When I get into stop and go is can climb a bit higher. Normally it has run at about 90 winter 95 summer.

I took out the thermostat as that is the easiest to get to and figured it was as good a starting point as any.

I put it in a pot of water with a thermostat to see when it would pop. I am looking at a pop of boiling water (212F right?) and it has still not popped. Does the pressure of the cooling system affect how/when it opens?

I took it out of the water and ran it under cold to see if I could push it open and I could. There was a decent about of resistance.

The bottom of the therm says 87C on it so it should have opened at 188F right? Or am I missing something.

I'm running MB coolant with a 50/50 mix distilled water. Both the main fan and secondary fan work. Primary is magnetic and it turns free with out resistance when not engaged and I have heard the secondary kick in when the A/C turns on or the engine temp gets about 106/7 or so.

Is the therm bad?

I was just looking at a conversion chart and assuming the car temp gauge is accurate, the therm is popping at about 223C or so. Since the system is under pressure, I guess that makes sense. Seems like a safe bet that the thermostat is broken.

Yes, that's hot. With a good thermostat and water pump you should stay a little over the 80 mark while driving and near the 100 mark sitting or alot of stop and go. Those are without a/c running so no auxiliary fans going. With a/c on, they may be a little different, but not much.