I've attached two pics.
The first one with the yellow arrow shows where my thermostat housing is leaking - coolant is bubbling through the top of the bolt where the arrow is. The area around the gasket itself is fine.
The second photo shows the mating surface on the cylinder head - i.e. not very good. I bought the engine newly reconditioned a couple of years ago but the build quality in some areas leaves something to be desired (the supplier shall remain nameless).
The mating surface on the thermostat housing itself is fine so I haven't bothered attaching a pic of that.
The last couple of times I've had the thermostat housing off I've noticed how bad the surface of the head seems to be in this area, but fingers crossed, it sealed ok both times so I've just left it alone.
This time though I've been through three gaskets in one day and just can't stop coolant from finding it's way up that one bolt nearest the rad.
Look closely at the photo and see that the gap between the bolt hole and the channel is tiny - looking at it, it's difficult to believe the gasket could be sealing properly in this area.
Am I right in thinking this is the likely cause of the leak?
It's never leaked before but I'm thinking if the material near that bolt hole was marginal to begin with it could have very recently chipped off.
How would I go about rectifying it? Would a garage have the tools to be able to machine it down a bit to give a new flat surface, with the head in situ (I really don't want to be taking the head out)?
I could use no. 120 sandpaper at home but I'm guessing that's far too much to ask of sandpaper, and it would be difficult to keep the surface even?
Quite why the surface is in this sort of condition I don't know - I've never used metal implements on it and only ever cleaned it with plastic scrapers. I also never figured out how bits of engine paint ended up in the middle of it.
I have just realised I have some spare housing studs and nuts in a bag (brand new), so I could try using those, but I really can't see how different studs would help if there's a leak in the first place.
I also read somewhere that in some heads the holes are drilled straight through to the coolant channels, and need a bit of thread sealant at the bottom, but if this wasn't the case then the leak would have been happening right from the beginning.
On a side note, what is the semi-circular indent for on the gaskets? It doesn't seem to do anything. I've been assuming the gaskets can go in any orientation.
Also, I have gaskets from two different suppliers and on both of them the third hole is quite a way out. Why is this? They're both specified for 998cc heads.
Thanks in advance,