Noticed this hole forming. I'm thinking I'll fill it with JB Weld.
Any other suggestions?

 

it might be prudent to drill the corrosion out then fill it .
I would put some tape on the backside to hold the JB.
Then mix it up,
Then put the JB in the microwave for 5 seconds,
then it will pour into the hole

 

Is there something I can put on it to clean it out??

Like fluoride Looks like a mean cavity.

 

Any chance you can get a sharper close up photo of the cavity clearly illuminated rather than in shade?

Inspection of the internals around that ocation tells me there was no general corrosion taking place so that rules out the usual mindless mantra of "it was spent coolant that caused it".

I certainly agree with Stan in that you need to de-burr the surfaces to prepare for any recovery work and you need to do this immediately before doing what you choose to do. If I had that problem I would use a Belzona product if was to go the two pack epoxy route- it is not a cheap product but nothing compares performance wise- I have used it to repair pump casings that operate at way higher pressure than the few psi this system sees. Tghere is one specific Belzona product that is specifically suited to this type of repair where the site may be contaminated somewhat.

My best guess as to what has caused this would be a casting defect. When I had my motor apart some 16 years ago following the loss of my late 90 S4 the heads and everything else were in perfect condition but there was something similar going on about the size of a dime wherein some material about 1mm in depth was missing from the internal surface of the water jacket outer wall. There was no bovious signs of corrosion and I figured the issue was due to a casting defect- the surface looked a bit like what I see on your photo but in your case it appears to have gone through completely. I you do use a deburring tool you may see more of the "metal" disappear if indeed it is contaminated with some kind of defect. I get the impression that the surface of the damaged area may be "blackened"= is that a correct observation or is it just a shade type of thing?

 

Personally I would just replace it with a good used or new bridge.

 

Newbie alert*
Why not weld it up?
Cheers

* meaning me, certainly not anyone on this thread... I just re-read and thought someone might interpret that differently...

 

IMHO, it's always been there. Thats just the raw alloy surface exposed and oxidized. If you wanna stop and hide, it, grind it out and around it the best you can, seal it. But its hard to really stop this alloy once exposed from spreading under your existing coating.

If it's dry, ignore it.

It's a casting void...this isn't a 1,000psi application.

 

Yes, replace it - I'm sure they're inexpensive.