there is some strange problem occured in my car during the last two days. the radiator fan works fine the temprature seems to be normal but the temprature gauge goes up. and even when i swith the lights on it goes more up. the temprature usually goes up at night time when the lights are on. i came to office in the morning with a drive of almost 20KM mainly on 4th and 5th gear with 80 plus speed and the temprature remains normal the whole way. but within city in traffice it goes a bit up in the day time as well and in nights it goes way up. turning the lights off it comes down aroung 3-4 mm. the mechaninc said its the problem with the some earth wire?? could it be the problem?? or something with the cooling system?