My dads mk3 escort with a 1.6 auto cvh on carb has developed a problem with the coolant.

Fill up the system, let the water reach all round the engine, thermostat opens, water reaches a good level, fan comes on and woooosh back to step one.

I have flushed the system, blown through the pipes and all is clear, no water on dipstick and no oil in the water... Even with the cap on the expansion it leakes through the overflow tube.

Getting a nightmare now