In line thermostat, I'm going to give it a try.
	
	
		I have been having trouble with over heating in my TD5 2003.
The temperature has varied from 85 deg to 130, then I am in trouble, there is certainly over pressuring that I did not think was possible.   An 18lb cap should release at that pressure but it does not seem to.
So, I have two main suspects, an overly developed ECU and no EGT gauge (yet), or a head gasket.
Any load on the vehicle causes spikes in temp, even driving through the hills on the freeway at 100KPH with no other load on the temp will spike to 120+.
Today we towed a trailer with a lot of wind resistance (portable toilet) and kept the speed under 80 KPH even down to high 60s at times going up hill and whilst the temp varied quite a lot (82 - 103) we had no problems with overheating.   The max it got up to was 103 but backing off and there was an instant drop.
Is it possible to retro fit a standard ECU to prove that (over fueling) side of things?
The third option could simply be the cooling system, I am in the middle of trying to fit up the 'American' solution, the only part of the cooling system that is unknown is the pump, but with the air bleed valve out it really sends coolant high, so it seems to me to be reasonable.
I'll report on any findings.
Regards
Mike