1stly many thanks to the suggestions posted previously about the problem with my Valmet combine harvester engine smoking and over heating.
Right we've had time to investigate some things (rain stopped play again )
We took the thermostat assembly out and found that it has 2. 1 is a std type rated to operate at 82 degrees C that was working OK but the 2nd is a double acting affair that not only opens to allow water to the top of the rad but also seals a gallery to the pump at the same time. This is rated to operate at 83.5 and when we tested it it actually only started to open at 96 which is a degree or so over the automatic shutdown system - doh! We managed to get it to start the shut down process in the hot weather and found that the top hose had collapsed under suction and that the rad cap could be safely removed cos it was so cool with no water circulating in the top of the rad.
Hopefully this should sort the overheating bit out.
As for the smoking bit my suspicions are turning to the turbo. It has occurred to me that if there was **** being blown thru it it could be worn resulting in it being down on boost. Its s'posed to run at 21 psi and I'm in the process of making up a tester to check it out - could explain some of it don't you think?
Cheers again, your comments were very helpful to uz ol farmer boyz