Cooling bypass help C5 II 2008 HDI overheating

[Cittotraang]

Hi.
I have a Citroen C5 II 2.0 HDI sedan from 2008 that Ive done some work on.

The radiator, thermostat, timing belt, water pump and all sensors for timing was exchanged during the winter.
When the cooling system was filled up again it was bleeded with success, heater on High and warmth coming slowly.
So, the strange begins. I´m driving the car up to 6 dots on the gauge and it works fine until I put load or going up a hill it overheats instantly with a grand red stop sign appearing.
The I just pull over and hear the fans coming to, seeing that it pushing out coolant thru the lid as the engine is clearly overheated.
With the engine shut off and the thermostat open I can fill the system again and bleed it to proceed to drive normally without any overheating problems at all.
So I have tried to find any kind of bypass that might have to be checked but there are so many small hoses and pipes that I wanted to check here first.
I have searched the archive with no luck and since I do not have a webasto, I do not see a matrix that might clog up.
My vin is VF7**************[VIN obfuscated, can be read by forum staff]
Have a great weekend.
Best regards
Andreas

[Cittotraang]

*Update* So, I have removed EVERY hose, one by one to flush and there is no clogs etc anywhere.
The heater has free flow. I can see that there is a circulation etc thru the engine.......
Any suggestions are welcome, it is quite odd to start, drive 10km so it overheats, refill it and bleed it so it works for the rest of the trip.....

[penners11]

You need to plug in lexia to see if the coolant mag valves are working/faulty. There is a a modified stat housing that dispensers with these (2 off), one in the stat and one o/s front of engine bay (follow the pipe from the header tank.)
Post replacement, lexia will show 2 faults for open circuit, ignore them, but the car will not show the eng mal lt.

[penners11]

p. s. I forgot to mention to modify the coolant return pipe to the header tank, I believe you can purchase this but I never found one. Or join the 2 Pipes together from the engine bay side.