Quote Originally Posted by IanY View Post
Yes, that is an Apogee GTX, and no the top is not copper, and no that is not corrosion. That white gunk is from your radiator. Clean it properly and re-install.
The stuff in that photo looks the same as the stuff that I found in a customer's block a few weeks ago... except, his block was caked with it to the point of killing coolant flow and performance. Below is a quick photo of the inside of that GTX's aluminum top after a thorough cleaning. According to the customer, there was no other aluminum in the loop and he was running straight tap water (which wasn't the brightest idea, but is beside the point).



...and the unnecessarily high-resolution version

From a quick inspection, the deepest pits in the top are around 0.3mm...

Now, I'm not saying that everybody should panic or anything like that because, really, how many of us run straight tap water in our loops? My point is that these blocks can and do corrode, despite the elaborate plating. So, in the future, perhaps we shouldn't be so quick to write off people's claims of corrosion (assuming, of course, that they can provide decent photos).