Check for any immediate leaks when you fill up the water. If these aren't visible, check your oil filler cap and check if the oil looks like mayonnaise, if it does then it will be the head gasket that has failed and you may find signs of white smoke from the exhaust. Failing that the water system could be over pressurising and boiling/blowing the water out of the water filler neck this can be identified by rusy water marks around the filler. It is easier to explain how to repair once the fault has been located.
Moz, January 2007
