Hi,
Yes well if you have used the dremel tool you now know never to use again!, only hand tools/scrapers and the likes should be used, I have used a solution of Muriatic Acid and water (5
parts water to one part acid)(always add the acid to the water!!) and flush try to let sit for an hour them flush again with fresh water-careful not to spill all over the
engine, this cleans the galleries out quite well but might have to do several times followed by a good flush,
Really the cylinder head should come off(yes i know that sucks!), in future there's a product called "Salt Away"which is used by the out board
boating community to flush there engines, it not only cleans out the
salt in the system but actually helps in prevention of further build ups if done regularly,
Please do not be tempted to run with out a thermo stat as they do an important job(if they didn't need them trust me they would save $20 and not install them) it should be replaced or at least tested in a pot of water heated on the stove- it should start to open @60c and be fully open @90c,
What do you plan to do about the hole?
Cheers Steve