Interesting Eric, as I am playing around with my cooling system now as well. It's hell hot here in Texas, and on one of those 102-degree days, I noticed my temp gauge hitting 105 while idling for a long time at the house. My aux fans are working properly, and maybe I'm just a little too anal, but I am used to seeing the gauge read about 85 or so when idling.
Temp is just below 85 when driving around town and on the highway, but it gets to just over 85 when I am stuck at a long light. In a hot afternoon, it creeps up to 100 at a long idle, and then over that if I am idling for more than 10 minutes. I don't remember what is normal for these cars, but I want to be safe than sorry.
I decided to do the boil test, and too, found that the thermostat was snug. I believe this is due to the fact that the system is pressurized, and there is a bit of a vacuum to contend with when removing it. I gently pried around the thermostat with a flat tipped screwdriver until I heard the seal release the pressure. Then it came out easily.
It opened up when the water came to a boil, but I don't know what is considered normal. I put the thermostat back on since I had to go to work a few hours later, but I guess for the price, I might as well replace it. My service receipt for the new water pump install made no mention of replacing the thermostat as well, so I guess it's about due. Make sure you top off with additional coolant, as you will lose several ounces of coolant mixture after removing the part...
[Edited by G-Benz on 07-17-2001 at 01:52 AM]
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car