Porsche Repair: Porche 944 Cuts out, porche 944, head gasket

Question
Hi there Dave , I have a problem with my 1988 944 turbo,it has run perfectly since i bought her but 6months ago needed the head gasket replaced. The car has now developed a strange problem, it starts perfectly well every time but within half an hour cuts out completly and no spark present. After cooling down the car will again start with no problems.,run for half an hour then cut out again , I have changed the complete ECU Computer to no avail. Any ideas would be appreciated Dave

Answer
Hi Ewan,

Could you help me out a bit...by the way you've described the problem, I doubt it's time related (the half hour increments) but it definitely sounds heat related.  Are you saying when the water temp gets to XXX degrees it quits?  

Don't know if you have an oil temp gauge, but if so, do you think the oil temp could be the trigger?

Dave