Water Jacket Clean Out Project

[Borrowed Time]

Thanks Neil, I agree that the open RWC system needs very little pressure to confirm no leaks. One thing I did learn during this process is that even a tiny bit of gasket or even glue on flange face of the thermostat housing will cause a leak. Will update after I fire it up this weekend. Thanks again to everyone for the encouragement and advice!

[Borrowed Time]

HI All! The update is SUCCESS! Fired up the A4 this past Saturday evening and it ran like usual with a little white smoke in the exhaust from the MMO that I had squirted into the cylinders when I took it apart a month or so ago. It has the normal flow rate coming out the back end, and after it warmed up and the white smoke cleared up, I noted no steam either. During warm up, engine temp climbed to 180 degrees and slowly settled back to 175.

Prior to my recent clogged up difficulties, the thermostat (original dual action in a newer Moyer housing) kept the engine temp right around 175 degrees. I ran a temperature experiment when I took the boat out on Sunday and closed the bypass loop valve completely. This reduced engine temperature 20 degrees rather quickly but having read that the A4 is happiest at 175-180, I decided warmer is better and so removed the valve from the bypass loop in favor of the simple hose between the T-fitting and the thermostat housing. I also found that with my newly cleaned out water jacket, I had the same volume of waste water with the valve in any position. Before I cleaned the mud and gunk from the jacket, the water flow in the closed position was reduced to a trickle. Fascinating thing is that the mud and the trickle together managed to cool down the block, but the steam in the exhaust was a flag not to be ignored and started me down this path.

So another success story thanks to the confidence and skills gleaned from all the helpful folks on this forum. Thanks!

[Borrowed Time]

Attached is a picture of my thermostat, taken within a minute of when I plucked it out of the pot while it was being tested. I can't recall the temperature of the water at the time, probably 200 or so, really just confirming that it would open and close normally. It seemed like it open a bit late, hotter than I thought it should, but seems to functions correctly best I can tell. Most importantly, it keeps the engine temperature within a few degrees of 175.

Can anyone identify this thermostat?