370z overheating please help

[David86]

Hi to all, Hope somebody can please help me this one is driving me crazy. I have purchased this 370z with an overheating problem, I have replaced the thermostat and now removed It just for test purposes, I have drained and refilled the system múltiple times using all the bleed processes I could find (bleed screw on radiator, very slow filling, high burp funnel and vaccum filling), every time I refill I have bubbles coming out of the system mainly after light reving of the engine (run for nearly 3 hours and still have bubbles), assuming It was going to be a head gasket I have done 3 chemical tests all negative (one on the expansión tank, one on the main cap, and one with little coolant in the system on the main cap) Also tested the tester by putting It in the end of the exhaust and It changes colour instantly) Also disconnectd all pipes etc and blown through with compressed air in case of a blockage. Any help would be much apreciated and I apologize if this posted in the wrong section. Many thanks.