range rover overheating

hi i have a range rover 4.6 v8 vogue on a 97 plate. it is overheating. i was told by a friend that the head gasket may have gone. so i am at the moment going through the process of alimination. i have just put a new therostat cannister on the car. i have run the car to operating temp. all was fine, left it running for ten minutes and the temp started to go up. i put my foot on gas pedal and the temp started to come down. can anyone help me out as to what it may be if it is not the head gasket. i dont know much about cars but know a little. could it be that the water pump may have gone. thanks

how high did the temperature go up before you put your foot on the gas pedal and it came down again?

you can have a test done on the coolant to see if hydrocarbons are present, this will confirm head gasket or liner/cracked block.

Are you losing water, either out the exhaust or in to the sump??
Bear in mind that the radiators are prone to causing overheating problems on motors with a good few miles under the belt and especially the water/anti freeze quality history is unknown