running the 300E cold

I notice that my 1989 300E gets warm very quickly. In about a half mile the temp gauge is already passed 40 but it does stabilize around 80 or alittle above that. Is that normal? Can I get a thermastat that opens at a lower temp so it runs cooler. I'm not familiar with import cars but I know that heat kills an engine. Would running the 300E cooler be wise?
The coolant is blue, can I used green antifreeze with it? Whats the difference between blue and green antifreeze?

That is normal operating temperature and must be at that temperature. As
long it doesn't go past 100 degree... you are good.