hi i need help i repaired my fiat uno 1100 motor 146 a9.000 the pistons and rings are now 76.4 everything else its standart it have brand new oil and water pump the valves are calibrated the radiator its new.... and its over heating, the radiator fan almost work all the time and it wasnt like that......i live in guayaquil ecuador its a really hot city around 38 celcius degrees in the morning... and the night its around 28 or less some time... in my country that kind of car use always oil 20w40 but i just read the manual and after the fixit i begining to use 15w40 please help i dont know what to do

I don't think the problem is the oil grade, 15/40 was the standard at the time of the Uno and other FIRE motors, it then became 10/40 semi-synthetic and then 5/40 fully synthetic. 15/40 will be a lower technology mineral oil so will deteriorate quicker but still give the correct protection in a hot climate (Italy gets hot also!).

You need to check the cooling system... air locks, water pump, thermostat, heater matrix. Also on some engines if you fit the head gasket the wrong way you can block some passages for oil and water.