engine problem again overheating this time !!!!

[filh]

I was rallying this sunday with my newly rebuild engine (600km done before race) .
Everything went well and the engine was really pleasant BUT......
2 stages before end of race, The heating gauge went in the red area , and oil was near 120°C as I was on the start line .
I started ans stop 500m further . The coolant in the expansion bottle was boiling and both up and down hoses were hard as concrete.

I manage to get the pressure out of cooling system , wait a little and poured about 2 1/2 liter of water in radiator . I restarted the engine and finished the stage without any overheating problem . I also achieved the last stage (14km) without any problem.

So what do you think : could a blocked thermostat be the cause ?
The cooling ventilator is well functional .
I forget to mention I stopped near a cemetary, and the water I added came from there Holy water ????? : :idea:

Phil