Why might a 1998 Fiat Punto S60 keep overheating?

Answer 1

The first thing you should do is check for an airlock in the cooling system, this is easy to do and costs you nothing, a severe airlock can stop the temperature sensor from allowing the cooling fan to kick in when its needed. I have found most puntos airlock in and around the heater matrix, one tell tale sign is if the engine is overheating and you switch the interior heater on the air blows luke warm for a few seconds then blows cold. Most people including alot of garages would then tell you the head gasket has gone and and charge a fortune to replace it.
The procedure:
Make sure the engine is cold or the car has been standing for at least 3/4 of an hour.
Follow the top hose from the radiator back towards the bulkhead, you will see two 25mm dia rubber pipes going into the bulkhead these are the hoses for the heater, Just before they go into the bulkhead there is one bleed s***w on each hose. Undo both screws, you maybe able to do this by hand otherwise use a flat screwdriver.
Remove the filler cap from water tank on the side of the radiator. Does water trickle from the bleed holes?
If not replace the filler cap and start the engine allow to warm up this may take a few minutes. do you see any water coming from the bleed holes, if you see no water when the temperature gauge is just above half way or if steam is coming from the holes, you have a sever airlock.
Switch off the engine. and allow to cool.
Remove the filler cap from the water tank and fill to top using either a hose or watering can. Start the engine again with the filler cap off the water should be sucked from the filler tank around the system forcing the airlock out of the bleed s***w holes. Top up The filler tank as this happens. Once you see water squirting (not trickling) from both bleed holes. Stop the engine and replace on bleed s***w. Restart the engine allow water to kepp coming out of the second bleed s***w until the water in the filler tank is at the normal level.
Stop the engine and replace the other bleed s***w. Replace the cap on the filler tank.
Start engine and allow to warm up if the problem was an airlock the temperature will rise slowly and the fan will kick in when required. Turn the heater on when the car is at normal running temperature the air should now be constantly warm.
Hopefully thats the problem cured and you still have £350 in your pocket rather than the garage till.
This is my experience only, don't attempt any of the above if you are a complete numpty, I wouldn't want to see anyone get hurt.  Regards Average Joe.