The 2.2 has a known weak spot around no.4 cylinder & this is where the majority of HG failures occur. With the engine running, check for bubbles appearing in the coolant expansion bottle, also take the cap off & smell the coolant, does it smell of exhaust gas? Are your radiator hoses rock hard when the engine is up to temperature? Does the temperature gauge indicate the car is running hotter than usual, or has it/is it overheating (red warning light on?)
Are there any signs of emulsified oil (mayonaisse) on the dipstick, or
large amounts on the oil filler cap?
For a definitive check, Run the engine upto normal temperature or take it for a run before going to bed, let the car stand overnight then remove the Dis pack & no.4 plug (the one nearest the cabin). Then either shine a small bright torch into the combustion chamber & see if you can see any liquid there or firmly fasten a piece of absorbant material (cotton bud etc.) to something like a kebab stick or pencil & lower it into the combustion chamber making sure it reaches the deepest part of the piston head & move it across from side to side before removing it & checking by sight & smell for signs of coolant. Repeat on the other cylinders if necessary.
