Okay so i searched for a similar problem i am having with my coupe, but didn't find any.

So here's the deal. When i drive my car it's fine, but when i stop for even 5 minutes on a stop light, or on a bumper to bumper traffic, i notice that the temp will start to go up. It stops at about 90% of the gauge (never reaches the red bar). Once I start going again for about 40MPH, the temperature will start to go back down to the middle.

I had my thermostat replaced, and the previous owner had the radiator replaced before I bought the car. She also had the water pump replaced with the timing belt. I also had a minor pipe replacement when it had a little leak on the radiator once. I also took the car once at a mechanic, he said "he THINKS" that there might be water in the engine. He started to unplug the spark plugs and check, and he put them back. The fourth spark plug was hard to take out so he told me there is definitely water there, so he didn't bother forcing it. For a while after that, I did not have the problem, but it eventually came back. With all this, I still have the same problem.

Before I spend any money, I would just like to know if the water in the engine IS the problem and would fix this problem that I've been having. Any help would be appreciated.