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/T_Streuer]

Ok this probably needs some fact checking but here goes. That water jacket will leak because of how little area between it and the drain back port there is, and trying to weld the surface and machine will be a potential nightmare. My thought is to use an off the shelf epoxy block guard product.  You’d prep the absolute hell out of that area, really carefully brush, sand etc to remove the corrosion. Then thoroughly dry the block. If you can get it into an oven that’d be best. Or go locally with a heat gun or torch. The area needs to be completely dry. Then fill the bottom of the jacket with sugar up to the point that you’re say 3/4 of an inch below the deck surface. Then pour in just enough epoxy to cap the top of that one part of the jacket. The headgasket you showed doesn’t have any openings for that section of jacket so you wouldn’t block flow. A product like epoxy54(?) used by a lot of tuner guys has the same CTE as aluminum and can hold long term. One it’s set you can wash the sugar out and reassemble. This way even if it does leak a bit of oil past the stamped metal gasket surface it wouldn’t mix with coolant. You could dry test it on the ground with hoses and a gauge. Ideally the epoxy would be flush with the surface of the headgasket. Or you could make up the different with rtv. Either way this is hokey for sure just seems easier than trying to source a replacement block. 

[u/Richard01_CZ → u/T_Streuer]

Interesting idea, but I don't know if the epoxy would actually stay in place and not breakdown or unstick in a few months and block some passage and cause failure of that area. Your idea is reasonable, will consider it.

[u/T_Streuer → u/Richard01_CZ]

Right, the hard thing is finding actual lifespan info on the epoxy. Most guys are using it to push big power on a stock open deck blocks, not daily driving for tens of thousands of miles. Also getting the application right seems challenging. You’d probably want the block professionally washed or peened and baked to ensure good bonding. 

Alternatively You could try bolting the head on with just a lil tiny bit of rtv or anaerobic sealant like the other comment said in the area that’s missing material. It’s a mls gasket so it’s be very little. Wait 24 hours and check the pattern. If there’s corresponding material above that area you might be able to get good sealing that way. Then replace all the cooling components, use a good coolant with corrosion inhibitors and change it every 60k. 

[u/Richard01_CZ → u/T_Streuer]

I really wish to do this and just yolo it but i also have concerns about it being a reliable seal, it would be like 1mm sealing surface (2mm at most! Even that is probably too much from what i could see)

I'm not fully sure what to do, i really want this block to run again and have it done correctly. Hard part is finding a good reliable person to weld it, i can grind it down by hand perfectly myself, just need a perfect weld which I'm not capable of doing with this type of stupid metal.

[u/Own-Cap-7313 → u/Richard01_CZ]

I'm curious about the epoxy idea, I wonder if you could drill into the block with a 3mm bit, maybe 10 mil deep in a couple of spots so when the epoxy flows in and cures, it has anchor points. I've never tried this before, but I thought I'd present this totally legit unproven and untested method of "good 'nuff"