merc5555

Hello everyone, i am new to this forum/site. So back in July i bought my first Merc, its a used 2011 C300 4matic sport, with currently 113k miles. Its a dream, its fast, its flashy, etc. Hasn't giving me any traumatic issues, yet. I reside in NY where it has gotten much colder this time of year. Today and yesterday i've noticed that my coolant temperature guage in the dash tends to go up as i drive on a cold start, which is fine, but during this time that it is warming up and waiting to reach operating temperatures (87-90 celsius) i've noticed that if its not at operating temperature and i come to a complete stop due to traffic, it will go down slightly, and it continues to go down depending on how long i'm waiting there, but as i get back to driving and give it gas, the temperature continues rising until it reaches operating temperatures/driving for about 15 minutes.

It has never overheated on me and when it reaches the operating temperature, i can sit parked/idleing and/or in traffic without the guage moving down or up.... What do you guys think this could be? My interior heat works fine. Coolant levels seem fine the last time i checked, no engine lights.

Could it be because of outside temperature change? Today and yesterday have been warmer at around 40-55 degrees Fahrenheit outside, it has also rained pretty hard though, when last week we we're at dry upper 20's to 30s-35 Fahrenheit.

Also what is the time a mercedes or any car should take to reach operating temperatures? Does it depend on the temperature outside? Or does it have to be around 5 mins as i read?

Any input would be appreciative.