The Nissan Path

Hi,

I've been rebuliding engine some 6 months ago, done head gasket, cleaned everything, new oil and water pump, new chains and all gasket sets.

Today I checked coolant at radiatro cap and found the light-brown film on radiator cap and inside radiator. Opened the top hose, which comes from engine, and it also has light brown film inside.
There's NO foam, and coolant is CLEAR BLUE, so I doubt it would have anything to do with ATF mixing.

I do NOT remember any such deposits to be found prior to engine repair.
Any ideas?
Should I do a few rounds of coolan flush?
Should I exchange BLUE coolant for something else?

I am also curious.. Hope one of the gurus comments

I would steer clear of any coolant flushes at all. If anything, maybe run some distilled water through it and flush that way.

I once ran a coolant flush through my 85 200sx. I was chasing leaks for the next 6 months. DO NOT use any kind of prestone flush or any other kind of snake oil. My opinion, YMMV.

What I see it normal residue. Coolant runs through your block, and over time there will be residue from the erosion and corrosion that happens inside the block passages. Looks very normal to me.

Coolant has anti-corrosive properties that decrease over time, hence the change interval for coolant. Otherwise you could run it forever!

I highly recommend Nissan Blue Premix. I've also used Honda Blue Type 1 Premix in the past with great success.