It may be fixed.
Last Monday night I drove the car 26 miles to my good friend Stewart's garage
http://autotech-garage.co.uk/ because I had run out of time (holiday was the next day) and patience. I managed it because I kept at 40mph and 70C - easy as most of the trip is motorway. As soon as I parked up at his garage the temperature rose to 90C and it cut out.
He has found the problem!! The large multi-wire round plug behind the distributor was soaked in oil when the high oil pressure switch previously failed. When I changed the switch I then gunked the whole area down - but I didn't (couldn't) take off the plug and clean it out. He disconnected and cleaned the plug and socket and has had it running for hours with no problem. He has also been using the car without it cutting out. He's using it again tonight, and then if all's well tomorrow I'll take the Porsche up for some work to be done on it and bring the GTi back here at normal speed and temperature.
I cannot recommend
http://autotech-garage.co.uk/ enough - he has looked after our family cars for 13 years and does a great job for a reasonable cost. He also doesn't take offence if I try to fix it myself and is always willing to give advice.
The problem is we've now got a spare GTi with all the new bits on it. We'll probably sell it because we don't need it anymore - we have a spare car so my son has now moved up to a Mini Cooper..... and I don't think he'll want to change back.
Thanks for all the tips I've received.
John.
