The thermostat is difficult to get to as it needs the timing belt removing to access behind it. I had a similar problem on mine and I simply drained off the old coolant by undoing the radiator hoses (at the rad on the n/side and at the thermostat housing on the off-side). Flush out as much as you can with a garden hose, run it through the radiator until it flows through clear. You won't get it all out cos' of the design of the engine. Reconnect the hoses. Refill with 2.8 litres of fresh anti-freeze (use the correct sort for your car) and, if it will accept any more, top up to the mark with clean water. Bleed air out through the temperature gauge sensor. Run the engine until the fan cuts in then let it cool. Top up with clean water when cool, if necessary. Mine runs without overheating after that degunging and it didn't need a new thermostat.
Ron
Chicks Fan, October 2008
