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The coolant that I used was Valeo Protectiv40 which is green colour.
I changed the engine coolant some weeks ago and the colour that came out was brownish (photo)
Also now the car has the same brand coolant.
But I see in the radiator that the colour is becoming similar to this on the photo at the new coolant too .
I am suspecting the water pump or the rear tube that goes from water-pump to thermostat housing to has rust.
What you say? What can be the problem?

maybe the previous owner was using tap water?I think this will diminish with some regular coolant changes

Was it a full flush or just the radiator you changed? I am thinking along the same lines, tap water or something. I never noticed this color using any green or blue coolants (ethane-diol?). I have only seen rust when using red colored coolant ... and that was no Honda engine.

But darn, if tap water was used you might indeed have started corrosion, probably the metal tube on the back of the block? Can't really imagine the thermos or pump will rust that hard, I assume these use steel with some rust protection... but that is just an assumption.

There was no tap water.
I had used Valeo Protectiv40 Coolant (green collour) for 2 years and now few weeks ago I changed the coolant and put again the same coolant (Valeo Protectiv40).
When I changed the coolant I flashed completely the system from old coolant.
I notice that the fresh coolant becomes brownish colour too
Can it be the radiator rusted?

check for any corrosion on the outer side.

Well, today I changed the coolant.
I put again the same coolant Valeo Protectiv40 to see want will happen.


*ps: the old coolant had brownish colour but there were no flakes of rust or other foreign particles
So let's see what will be the evolution of the new coolant in the next days.

Update:
The new coolant colour was becoming to change again
Today I checked the water pump but it doesn't have rust.

So other possibilities for the problem might be:
1) Rusty radiator or
2) Rusty water-pump to thermostat housing connection pipe or
3) Head-gasket
4) Rusty Interior Heater Core


I want to hope that is not head-gasket!
Now the next check processes will be the connection pipe
Then if it is OK I plan to check the head-gasket with special fluid for this purpose
and unfortunately there is no method to check the rusty radiator or heater

Was your car imported from Germany or so?

Yes, it is imported from Germany.
But I can't relate your question with the coolant issue.
I don't think that's matters because the radiator doesn't leaking.
If there is rust in radiator it is inside but it is unpossible for me to check it somehow

Maybe the guy was using plain water instead of coolant and now you have corrosion in your engine (worst case scenario). If you wash the radiator? In this was you could understand if this dirt comes from there. In any case change coolant as frequently as possible so as to wash away the leftovers. Buy cheap coolants for this purpose