You guys had a great thread on this back in 2015, but thought I'd better start a new one.

I want to try the vinegar flush described by HG. I just have a couple of questions:

1) If I remove the thermostat (raw-water-cooled system) and fill up the jacket with vinegar, am I right in thinking that the jacket is a contained space, with no connection to the rest of the engine? Therefore if the hoses at the Y intake are lifted up high enough there will be no overflow even if the jacket is filled to the brim?

2) How far does the jacket extend? I gather it must run all the way to where the anode is. Does it also connect to the exhaust manifold? I've got loads of crud in there, but of course I'm nervous about the possibility of getting water in the engine. Are the water and exhaust sections of the manifold separate sealed spaces?

Last year when I opened the two drains there was a lot of crud, and I made the mistake of leaving the plugs out, with the result that I had trouble getting them to tighten sufficiently in the spring to seal the drains. Actually had to use an o ring on the manifold drain to get it to seal. Good news is they came out again no problem yesterday. This year I want to do the job properly!