open the bonnet, its a plastic round bottle at the top right hand side of the bay. If its empty, most likely to be hgf. fill the bottle up to the centre (maximum) mark and check for any oil slicks on the surface. Check the underneth of the oil filler cap for any yellish slime (usually reffered to as mayo) and also dipstick for mayo. If you have any of these symptoms get a pressure check done at a garage to check for head gasket failure.