Ok, when it is evening the temp stays normal. But during the day when it is hot outside the engine gets hot. Is it possible to be the thermostat?? Why doesn't it get hot at night then? I know the cool air is the reason, but could this be anything else?? Does anyone have an idea or experienced this?? Let me know please and thank you. I think I will change the thermostat anyways and see if that works.

 

It is not the thermostat in water pump or you would heat up high at night. You are right at some edge in cooling efficiency depending on how big this day and night difference is but since you don't go out of control during the day I would mark it down to age showing.

If the radiator fans are switching on at the same temperature day and night, that should be OK. If you are running the A/C during the day that would explain it as the condenser is dumping heat into a big chunk of the radiator.

Otherwise, you could try a system flush and chemical cleaner to get efficiency back up and use Water Wetter in the coolant afterwards.