Start the car with the expansion tank lid off. Let the car get up to temperature then refit the cap. Keep the engine running say at 2000 rpm for 2 minutes. Stop the engine and check f the coolant pipes are not hard. If they have pressurised it is a sign that the HG is away.

Take it to a garage and have the header tank fumes checked for combustion gasses. If your car has an oil cooler this may also be a potential problem area.

Regards Peter

It could be, but before you leap to this conclusion check carefully and be methodical about reaching a diagnosis

It is possible on a car of this age that you could have 2 problems:
1. Could be mayo under the oil cap due to cool running in cold weather
2. could be corrosion in the coolant 'cos it's never had a coolant change

Have a garage dip the coolant to check for combustion product as a first step and carry out a compression test.