As I have mentioned before, I think I have a bad thermostat and so I am told by others, as my car (85' 380SE) was running very cool on the highway when it is cool out... the cars gauge is like @ 60°C. Now that it is warming up, I have noticed the gauge is going much higher than it did last summer when idling. Tonight, I was setting in a drive-thru and had to idle for about 5 minutes. It was 58° outside. When I looked at the gauge, it was up to about 105°C! It was not in the danger zone, as I would not have allowed that, but I "revved" up the engine to about 1500 RPMs (to get the fan to speed up) and the temp gauge went down almost instantly down to 85°C, which seemed odd it went down so quickly. With that, does it sound like the water pump getting weak, or will a faulty thermostat also make an engine run too hot when idling, when at the same time run too cool when cold out? Today, when I was driving when it was 67° outside, it was around 80°C, which seems normal, but it goes up and down quite a bit as I stop and go. Last summer, it never went above 95°C, even in 97°F weather, but seems like it may be worse this year.

I would like to add this info and be sure before I replace the thermostat.

Thanks in advance!