Geoff,
you may find that the 'Temperature Sender'
& the 'Temperature Gauge' (Tdi) are a mismatch.
Is the engine actually getting as hot as the Temperature gauge indicates?
Originally when i first got it & was concerned i used 'Water Wetter' in the coolant system as a quick temporary measure,
Then i found that the temperature in the system wasnt actually that high,
certainly not what the gauge showed when going into the red..
(so drained it & used it elsewhere
)
A better gearbox oil cooler might also be worth while.
george