The radiator cap is on top of the expansion bottle, under the bonnet. Renault antifreeze is yellow in colour and this should guide you. Radweld is ok to use in the radiator but it should be a temporary fix - it can gum other things up such as the thermostat. Look for crusty deposits where you suspect the leak to be - popular areas are the heater matrix and water pump, if yours aren't obvious.
John, December 2007
