AU I6 cooling system

[Road_Warrior]

Gents

The Mrs' bunkie doesn't seem to like hot days now that they're here. Spews a fair amount of coolant out of the header tank overflow. Temp guage doesn't seem to go higher than the 'O' in the N O R M A L writing on the guage, but the amount of coolant coming out suggests something else is going on. Both of the thermofans appear to be working.

I may replace the radiator cap and see if that makes a difference. It has the Ford 120kPa unit on there now. Should I do the thermostat as well? Parked on a level surface with the engine running, the bleeder hose that runs from the thermostat housing to the header tank is working overtime shoving coolant into the header tank - is it supposed to be doing this?

Radiator was replaced by Natrad last year, for the previous owner. I would assume they did a flush at the same, time, the coolant colour looks very clean and blue.