cooling system?

Hi my friend has a M reg, 1.4 Automatic, Vauxhall corsa which is over heating, I tested the fan wiring it directly to the battery, to which it worked. Replaced the radiator thermostat fan switch too. The fan still isnt coming on. The pressure seems to be building up in the expansion tank. I think its either the rad is block air or debris or the water pump is duff.
I have heard a couple of people say that the plastic impella starts to slip on the water pump too.. therefore can not provide enough pressue to circulate the water round the cooling system and engine.. what is the best thing to do and test.

any solutions and ideas would be highly appericated..

Rick
January 2009

Proably need to put pressure tester on it .........look for leaks after car is hot ......can put down cardboad and drive car on it and look for anti freezw spots in morning
There is a coolant dye they make but to use it you will need a black lite

bg
May 2007