Can we talk (capillary) temp gauges? I mean both the VDO 444, and the VDO 544/120 kind. My '57K has been showing a serious overheat, but the car doesn't actually boil over. I may have a silted up (early honeycomb) radiator, and I'm dealing with it as if that were the problem (plus checking valves, resetting the carbs, timing, backflushing the block, etc.).
But, I have a suspicion that the gauges may not be "binary" i.e. on/off/good/bad.
Can they also gradually go bad, and misread? I know that if the delicate capillary tube is compromised, then the stuff inside escapes, and instant no go. BUT, does it sort of (mal)function if, say, the car did actually seriously overheat? This is the early white background 444 type, but this has also happened in the later types.
One of my symptoms is a rapid needle climb to the right, but an occasional drop to about 3/4, but then it surges back to the red. Oh, after a vigorous drive, the radiator is too hot to touch at the upper tank and hose, but a lot cooler in the area of the lower hose. I boiled out the radiator and the heater core in the hot tank overnight, but this problem still persists. My next move was to have the radiator rodded out. I've removed the heater from the loop, and have also considered the cup of muriatic acid in the coolant trick. Hmmmm?