Guys, have a related question, although you posted over a year ago!
Have noticed my coolant level has gone below MIN mark and on motorways the engine temp just keeps rising. Can I just top up with normal 'bought in petrol station' coolant and antifreeze until it goes in for a service soon or do I need to flush and replace/test etc?
You maybe have a radiator problem, or the thermostat is stuck.
I'd top up with a branded antifreeze, but its not really going to affect the overheating if the radiator is on it's last legs. Do you see rust and white powder on the radiator fins?