I went to a mechanic, don’t want to mention any names and after he did a flush and put a new antifreeze into my 240, my car sometimes goes 3/4 of the way up and then down to the middle. I had to take it back once to him and I guess he let the bubles and air out of the coolant. The car was fine for about one day of me testdriving it. Today, It started to overheat, it fkin goes up and down? Did he fck up something, like thermostat or what? Anybody knows where the guy from Nizztex is located, I know its somewhere aroudn Lawrence and Keele, can somebody pass me his phone number and address? You help guys is much appreciated.
Could be your rad is plugged up… happened to my silvia.
It had a higher water to antifreeze ratio so it ran fine until I flushed it and put 50/50 in, then it started to overheat like mad 
let the car cool down, open the rad cap, pour in coolant until it pours out, let it sit for a second, then do it again until the coolant no longer empties slowly, put cap back on. Grab the coolant hoses shake them … not too much so they rip off. Fill your coolant overflow tank to the top.
go for a short drive, and do it again, keep doing it until you no longer have to do it.
There is a procedure on how to bleed it properly, but this method worked for me … took a few weeks though, and coolant would mysteriously disapear from the overflow tank, but then it stopped once all the air bubbles got out.
if your car ran fine before then the mechanic must of done something wrong for sure. he never bled it properly. jusdgin by what you said that could only be the reason. make him do it right my 240 's temperature gauge goes to the middle and never moves one bit
and i did a flush about a month ago
The problem has been fixed. I let it bleed for few min, bubles came out and now the temp gage is just slightly below middle. Thanks guys for your help.