Life gets in the way, so it's been a long time between updates.
Got the radiator flow tested. It has good tanks and a modern core. Factory spec is 28-32 gpm; my radiator flow tested at 12 gpm. Thought I had my smoking gun.
Installed a different radiator, along with a freshly rebuilt waterpump, same symptoms: the car is happy and operates at 160-165F at any and all speeds below 45mph. Any increase in speed, and it starts to get hot.
For my load test, in 55F ambient weather, a 15 minute sustained run at 50-55 mph (on the freeway so couldn't go much slower!) resulted in a car that got up to about 200F, and stayed warm until I could park and let it cool off.
I know that one solution would be to never exceed 35mph, but that seems ridiculous, and the car is designed to go faster. Plus, where I live now, and where I am about to move, not exceeding 35mph means getting run over/in an accident or never driving. Not acceptable!
Currently away from home again for work, and getting ready to travel some more, but I have three lines of thought.
1. The car didn't overheat before I fixed the rich running condition. Edit: went back and found this from the summer of 2019 - "Drove to a friend's house, with the whole family (and hood back on!) and she ran just a nudge above 180 the whole way. The drive was in the mid-afternoon with a heat index of 117 and lots of idling at traffic lots. Very pleased. On the way home, nearly the same conditions, except had the headlights on."
This was with the heat riser wired open and the car still running rather rich. Fixing several exhaust leaks, which I suspect acted as a sort of "bootleg" heat riser system fixed the rich running condition. Now it overheats in cooler temps at sustained speed. Is it possible that at high speed (i.e. high load) the car is running too lean? Might see if I can get some sort of exhaust gas analyzer setup to test this, or just new plugs and an immediate speed run? Maybe the main jets are the wrong size? The carb was rebuilt a few years ago, and the main jets are sized per the book (looked when I was running too rich, see here: https://packardinfo.com/xoops/html/mod ... &order=ASC&status=&mode=0
) The plugs are a "normal" rich chocolate brown, but my thinking is that the darker color could be from idle time.
2. The new to me radiator also doesn't flow the right amount. It's a new core, but the core is a crossflow type designed for service in heavy and/or stationary equipment. It was built as an experiment to try and obtain better performance than the stock radiator at slow speed/idle conditions, i.e. a parade. No hot weather for stress testing right now, but initial indications are good. To test the incorrect radiator theory requires throwing my checkbook at the old radiator for a re-core, which I need to do anyway, and then re-installing a radiator with the correct core.
3. Something else on the car is causing the engine to work too hard, thus building too much heat. I don't even know where to start here. The oil pressure is fine, no sign of heat on the brakes/hubs/etc, the exhaust system is new within the last five years.... I have no ideas on this line of effort!
... obviously if anyone has any brilliant ideas, or wants to just spitball with me, I'm all ears! ...
In other news, I also replaced the generator bearing (it was original, and started howling) and installed new brushes. The generator bearing is a National 203FF, $8 from my local autoparts store, and I believe may fit most generators. Updated the parts cross reference accordingly. Also put in new brushes, but they weren't exactly a factory fit. The terminal post insulating block failed; I have a temporary repair installed but will need to find a permanent solution. I may re-brush the generator with NOS brushes when I do that, but it's charging just fine for now and the car overheats anyways.
If anyone needs me, when I'm not busy with work, I'll be over in the corner, hitting my head into the wall.
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