Engine block housing for thermostat unit.

[Frank3]

I am having replaced a corroded thermostat unit but in the curved housing in the engine block there is a small hole. This hole is about 3mm diameter located underneath and at the top of the housing. It appears to have been brazed/filled at some time, and now the piece of filling has fallen out.
Is this normal as I cannot see the function of it. Any ideas please.

[hands_aus]

Hey Frank,
If you took a pic, please post it.

There are places on the block that have threaded holes all the way through.
They are usually holding components like the water pump, timing chain adjuster etc to the engine.
The threads need to be sealed with a sealing compound.

Do a search for 'leaks'

There has been many discussions about fluid leaks on this site.

[Frank3]

Thanks Bob, will do as you suggest.