Hey Guys,
+1 for Tom's approach, but I was worried about someone "fiddling" the setting on the valve, so I went to the 1/3 + 2/3 Cooling fan setup... I can "see" if the things are working or not...Also +1 with "upgrading" the pipe diameter, in my opinion, do that first...
A rule of thumb: Low Profile radiator or using heat exchanger/restrictions in the coolant path, use biggest piping you can to aid flow, High radiator, you can get away with smaller piping as the thermal mass/coolant density difference gets a bit more forgiving... Also, use the biggest radiator you can find, its easy to block fins or throttle flow to downgrade it, but its a real SOB to make a smaller system work harder, which seems to be happening in your case Bruce... Possibly, just maybe, the upgrading of your pipe size to the largest you can fit would be the easiest to do and solve a lot of your misery...It certainly wouldn't do any harm, and shouldn't be too difficult to implement either... Probably, also, the most viable from an expenditure pov too..If you can, try and get away from the thermostat for the hydronic system, while it works well when it does work, hydronic+Tstat don't like playing together and need a bit, sometimes a lot, of tweaking to get things happy...(again, just my opinion...)...
Back when digital cameras and the internet hadn't even been thought of, I bumped into a farmer who was having a problem with his Lister cooling, his case was that it was cooling too well, it had a crank driven pulley/fan system... He settled on an interesting and unique, but a little tricky solution.... His header tank on his radiator had a large opening.... It was about 4" if i remember correctly... He had a toilet cistern round float attached to a few little levers that controlled a "shutter" on the radiator air side... as the temp increased, the water level rose, the shutter opened, allowing more air through the radiator fins and vice versa... He controlled the temperature of the beast by adding water to the header tank, more water gave more opening on the shutter... Was a cute, but in my opinion, not the best solution, but he developed it and was having fun! (The downside was, if he ran low on coolant, the shutter closed up and made things worse)...
Again I ramble...
Cheers
Ed