Note: Even if you don’t live in New Zealand here is some useful advice!
Having checked everything people have suggested to improve my cooling with no change, I pulled the rebuilt radiator and the water pump and took them to Trevor French Radiators in Auckland (www.trevorfrenchradiators.co.nz ).
He saw nothing wrong with the water pump, so he suggested that he unsolder the radiator and check it out. First they put a hose into the top, and water flowed out the bottom, but he said that did not mean that it was travelling through the cooling fins. Not sure I understood that one, but as it turns out, he was correct.
For a fixed fee of NZ$90, he completely disassembled it and found the engine rebuild resulted in debris that had blocked the reportedly rebuilt radiator. He rodded it out and soldered it back together. He began at 2 pm and handed it back to me at 5 pm with a fresh coat of black paint. He also recommended that I take a woman’s nylon stocking and put it over the entry of the upper hose to catch any more debris.
He also said that the radiator design was quite good… more sophisticated in construction and should last another 30 years before needing attention.
On reinstalling it, I hooked up a second capillary temperature gauge and discovered that the Smith’s gauge was reading 140 C while the aftermarket gauge was about 93. Without that second opinion, I probably would have presumed I had not cured the problem. Unlike previous runs, the engine was not making those noises related to high temperature, so I am more comfortable that it is running in the 90’s. The fans going off and on seem to agree,
After a few runs up and down the hill, I pulled the upper hose off to inspect the nylon stocking. I found significant debris, blue engine paint and other junk that would have contributed to the need for a 3rd disassembly of the radiator.
Advice to others in the future…
1. When you install a newly rebuilt or cleaned radiator, or if your car has been sitting and may have built up scale in the engine block, use the nylon stocking trick to protect the radiator.
2. If the car overheats, it is easy enough to remove the Bristol radiator and have a shop take off the top to check for any obstructions to water flow. Even if it was just rebuilt, it could be blocked again.
3. Do not rely on the Smiths temperature gauge. The engine block has nearby places to add a second temperature gauge, which costs less and is more reliable than an infrared gun.
4. Other advice they gave was to never use a water blaster that comes near the radiator fins. It flattens and does damage. I’d never given it much thought, but it makes sense. He showed me an example.
Finally, anyone in NZ needing radiator work, these guys are highly recommend. Three older fellows, all white hair, the oldest radiator in the shop was from a 1927 Alvis. Good prices, great service, super knowledgeable.