After running the engine for about 10 min the engine temp needle will slowly begin to creep up. I've checked to see that the fan is op and it is. Replaced the engine coolant temperature sensor thinking that may have been the issue (no reading on the multimeter when tested) and I still have the same problem. When it begins to overheat sitting at idle I can place it in park, step on the gas, and the gauge needle begins to move down. Is this a thermostat issue? Thanks.