Well this is my first post seeking advice.....
Today my car (A4 1.8T Quattro AVANT) overheated, has never done it before. The temperature guage sped up to 130 and the coolant warning came on, I had just sat in a traffic jam for 15 minutes but was well clear of it when it happened. I limped to a petrol station and took a look. The coolant was all where it should have been so I slowly cracked the cap open and let the pressure out, it seemed like quite a lot of air came out. I let it cool a bit and turned home, as soon as there was any strain on the engine the temperature was creeping up again and then dropping when idling. Stopped and looked at it again and noticed that the radiator was cold. I left the pressure cap cracked open and carefully limped home, the temperature was better with the cap undone but as soon as revs went over 2500 it started to come back up only to go down again when idling. When idling the temp was showing nice and stable in the middle of the guage as it should. Also the heating was on and off, would blow 'hottish' one minute then be stone cold......I'm thinking thermostat but that only got changed about 6 weeks ago so unless the new one is faulty it shouldn't be, only other thing I can think of would be trapped air but again I ran it with the pressure cap off so surely it should have cleared out......I'm stumped so would be very grateful for any advice