[Robby]

OP?

You are describing the buildup that occurs on the relatively cool walls of the plastic surge tank. Called 'Phase Separation' it is the visual of the coolant breaking down.
The ideal approach, if you are concerned, is to disconnect the hoses, remove the surge tank, and wash and rinse a few times....I have found Simple Green works ok.....so does a bit of dish detergent.....shaken, not stirred heh heh.

Some coolant will be lost if you take this path.

You have no real problem taking place.....more of a annoyance.

Rob

 

[Robby]

In that case, I'd think a drain and replace would be a good idea. The 2012 owner's manual says to "Drain, flush, and fill engine cooling system" every 5 years. The 2015 says "Drain and fill engine cooling system", every 5 years. Either way, for a 2012, there's a good chance that it's due.

Since the OP indicates a water pump replacement has taken place it can be reasonably assumed new coolant was installed in conjunction.
However, even with a chemical flushing process, the coolant in the surge tank gets changed but there is no actual 'flushing' action.

So, back to a formal remove and washout..........BTW....I have to do this to cars that I show about every two years. Surge type or overflow, both designs build this 'mung' on the tank walls.

Rob

 

[Robby]

Oh my!
That is a lot more evil appearing than I expected.

In general, a failed head gasket near a water passage will show as coolant intermixed with oil....known as a chocolate shake.
Rather rare failure though.....typically four bangers fail the gasket between adjoining cylinders....usually between #'s 2 and three.
It can happen where a high oil pressure passage going through the gasket (think cam bearing feed passage) could fail near a water port but this is highly unlikely. All other oil passage ways are for return and are not under pressure.
So, although not impossible, I'm doubting a head gasket failure.

I have seen coolant intermix with trans fluid in the radiator though and, if you have never changed the trans fluid it becomes rather dark.
This can occur if the trans cooler, built into the side of the radiator, fractures. Because the trans operates at much higher pressure than the cooling system, trans fluid gets forced into the coolant.

With this in mind, DO NOT pressure test the radiator unless the cooler lines are removed from the connections. Otherwise, you will force coolant into the trans.
Under pressure, lines removed, you may find coolant (takes a few minutes) begins to drip from the cooler outlets.

This would require a new radiator (obviously) and a immediate trans flush (since you can be assured a bit of coolant is in there).
The adhesive that is used to hold the friction material to the clutch plates is water soluble and you are hoping the water that may have made it in there has yet to cause damage.

Not intending to freak you out, but the photos indicate the need for immediate attention.

Rob