What is this? Should I be concerned?

[bligh]

I started a new thread for this as I am hoping to get as much input on it as possible. Or more precisely, I would like really accurate information about this.
I have been cleaning the core of my aftercooler for the last couple of days. I have used soap and hot water, vinegar and brake cleaner on it. This is what it looks like.;

But notice that on one end the is some sort of material in the first half inch or so of the top of the copper fins. De-greaser didn't take it off, vinegar didn't take it off, and hot soapy water pumping across it didn't work either. At first I thought it was hardened grease from the original install (it may be that) but I thought that the hot soapy water would loosen it up..Does anyone know what the white substance is and how concerned should I be about it?
Thanks
Scott

 

[caltexflanc]

Looks like it is at a place where the cooler fit into the housing. Have you tested it? A good radiator or diesel shop could have saved you time and heartache on this project, BTW.

 

[bligh]

Looks like it is at a place where the cooler fit into the housing. Have you tested it? A good radiator or diesel shop could have saved you time and heartache on this project, BTW.

Well, it is near where it mounts to the housing. But what is it?
There is only love in this project, Caltex. No heartache here. And really not that much time as I have my pump set up to wash it without me being there.

 

[Nomad Willy]

Looks like where the tubes are soldered on to the ends.

The white stuff (silvery looking) is solder.

 

[Northern Spy]

Yup. Tubes brazed to tube sheet.