I haven't been good about looking for petcocks. This is easy - few seconds with a screwdriver on 6 hoses. Of course the potential exists for hose to break, but not really a big deal if it does - hoses are cheap.
No overheating issues yet (thankfully). For the boat, my general philosophy is "if it ain't broke, don't fix it. If it is broke, maybe fix it." Not taking this thing to Europe.
You want to open the petcocks. There should be one at the center-bottom of the block water jacket, and typically there is at least one, and often 2, on each exhaust manifold/ riser set. This is as much to protect the petcock itself as anything else.