My car temp gauge starts to go up to the overheating area when I sit in traffic for a while or stuck at a long stop light. When I start to move again it seems to go back down to the normal range. What can be causing this to happen?
First thing I do in any overheating situation is check the coolant/antifreeze level in the radiator or the overflow bottle if you can not see inside the radiator or have an old fashioned radiator cap on the radiator itself.
Low coolant levels can cause this type of overheating so rule that out first. Now, if you have to add a good amount (say anything more than a cup of water/coolant) then I would be suspicious of a coolant leak somewhere. If you can not see any coolant leaks with your naked eyes, then I would get a cooling system pressure test which will help you locate the leak.
If the coolant level is full, and you are sure there are no leaks then check the electric cooling fan motor located on or near the radiator. That fan should cycle on and off as the engine temp heats up. So if you are sitting at idle and the temp gauge starts to move past the half way normal mark the fan should kick on.
If the fan does not come on, it can be a problem with the fan motor itself (usually is), of the fan temperature sensor or relay or a fuse that is not sending power or the proper temp signal to the fan motor to engage and come on.
I made a video talking about the different types of engine overheating and how you can determine the source of the problem yourself, take a watch now and see what you can rule out.