I'd say your head gasket MAY have gone..
the 1800 petrols are renown for failing head gaskets and they usually bridge across on the water galleries...you wont see emulsified oil because the water is actually being burnt off in the cylinder........in extreme cases you get water emission from the exhaust tail-pipe...but that IS extreme
any decent garage should be able to detect exhaust gas in the coolant if it has.
good luck with it
Richard
RICHARDS RESCUE & RECOVERY 07707-200-999
July 2008