Hi guys (again) If anyone's been keeping track I'm having some trouble with the cooling system on my Ibiza. I had the water pump replaced as I was loosing coolant and it turned out that was the culprit. NOW for the new issue! When driving home today the heater was blowing out lovely tropical air but all of a sudden it turned Arctic. Checked the temp gauge and I was running at about 100 but slowly went back to 90. I had this for about 15 mins (10 miles) then I got my heater back and the temp settled. No coolant has been lost (quickly checked when I got home) but I could hear a slight hiss/bubble coming from the expansion tank. Could I have a faulty thermostat?