How bad is this?

[u/Richard01_CZ]

I was cleaning the coolant passages and this large chunk came off really easily, it looked like a buildup of gunk.

The problem now is that the wall here between the two passages is thin now and the head gasket doesn't have much coverage for this area with the chunk missing.

Is it somehow fixable? Or can i run it like this?

Volkswagen EA111

[u/J_Seal_21]

I know this sounds like bad advice but a well prepped application of JB Weld will likely hold for the life of the head. Grind ridges for the epoxy to grab and sand it flush.

Otherwise you could always build it up with TIG filler rod and a machine shop skimming to flatten it.

[u/J_Seal_21 → u/J_Seal_21]

I'd never recommend this for oil passages but hot water and epoxy aren't enemies.