Like Cees, what I am about to relate is not about my Pagoda, but germane to the conversation.
I thought I had some kind of coolant leak in my '56 Dodge V8 pickup with only 13K miles, as I was constantly topping up the radiator. I would notice the gauge would read higher when going up the mountain but settle down a bit going down and stay down on the flatter roads. However it was a pain to restart when fully warmed up unless I raised the hood when I parked it. Even though I had drained and replaced the brown coolant last spring it was brown again. Last fall it overheated on a longer run on fairly level ground. Once it cooled down I pulled the thermostat, refilled with water supplied by a passing neighbor and started to drive the remaining five miles home. It overheated again barely half way home! Another neighbor passing by on his way to the dump came back with more water. I let it cool down again, refilled it and got it the rest of the way home before it got too hot, drained the remaining (brownish) water once it cooled off and parked it for the winter.
After talking with a couple of locals who knew the truck before I bought it, the consensus was the culprit was a silted up radiator. Sixty-five year old Dodge pickups do not have quite the same broad parts availability as Ford or Chevy pickups of that era. Going on-line, I found a place down in Alabama that makes custom and reproduction radiators, and had a new one made (made in the USA!) and UPS delivered it 10 days after the order. Last weekend Lucy and I pulled the original honeycomb radiator and installed the new one, which was a perfect fit, and a new thermostat. The gauge reads rock steady up and down the mountain, it starts up right away after coming out of the Post office or the store without having to raise the hood when parking it, and the coolant level has not dropped or changed color after a week of constant use.
Low mileage vehicles that have spent most of their decades sitting in wait of the next occasional drive can have problems, too!