heater blowing cold air

[KENC]

If it's not your rad, it could be pushing out water under boost through the expansion bottle. If you haven't any heaters that means you have been running it low or with very little coolant.
Problem can be if it's dropped a good bit in coolant the temp gauge will not read high as no fluid will pass the temp sensor in cross over pipe, and it's only when the engine casing gets extremely hot to the point of it going to lock up that the temp sensor will start to read high...

 

[gsr owner]

Thanks folks for all inputs, left car down today in garage, hopefully just the rad, as it would have pi**ed me off if the head gasket was gone, as there are only 83000kms on the car.
Alan