A key "moment of truth" during the re-assembly of my engine is the cooling system pressure test. Following Dave Stragand's advice, I hooked up a small pump the the overflow bottle to pressurize the system. The first thing I note is that I do not have the right bottle. This was a recent discovery. Mine appears to be out of a late 80's/early 90's Mercedes Benz. I went one extra step, spraying a soapy water solution around key points (head gasket mating areas, water pump connections). I also removed the thermostat before sealing the system because it's my understanding that with the thermostat closed (cold) I'd only be testing one side of the cooling system. This test is also supposed to help me determine if I shifted a piston liner, ruining the seal underneath. The results? 1. I had 3 leaks on the water pump due to crappy clamps. Fixed. 2. One -tiny- leak at a head mating surface in the "valley" on the driver side. It leaked at a rate of 3 bubbles per second, I was able to tighten it down to a rate of 1 bubble per 2 or 3 seconds. Perhaps when the metal expands, and contracts and I perform the re-tightening procedure, it will stop entirely. 3. One leak on the passenger side head towards the front of the car. Even smaller than the other one, I watched it actually stop leaking completely on it's own. 4. The worst leaks were from micro fractures in the overflow bottle. I sprayed it down and it bubbles in several places on the top. I was unable to hear -any- hissing from inside the engine that would indicate an internal leak. It takes a considerable amount of time for the pressure to bleed off through the cracks in the overflow bottle. The rate of leakage from the bottle is consistent with the time it takes for the pressure to drop to zero. That is, the bottle doesn't just give 1 or 2 bubbles while the pressure drops quickly because of another leak elsewhere. I realize that this isn't very scientific but I don't know what else to do. I think I've done ok. I welcome any suggestions. I know I have to replace the coolant bottle. I saw one on Ebay that was pretty reasonable. The guy only wanted $400.00....;-)