Hi Phil, if you have the original timing chain extension “water pump spacer” there is an internal flaw in its design that diminishes water pump flow and contributes to overheating at idle. As was mentioned by 55blacktie Chris Ames did formal thermal dynamics testing on a prototype he developed, and proved his theory. Chris published the results of coolant flow tests at specific engine RPMs, comparing the original spacer with his design, the results are quite impressive. I was one of the early purchasers of his replacement and met him in person at a regional in New Jersey a couple years back. I have it installed in my 312 and it’s all he says it is. I have a six blade clutch fan, Griffen aluminum radiator and a 170 degree thermostat. With Chris’s spacer I don’t run over 170 degrees which is approximately 4 fifths of the way to the end of the solid white line, the end of which is 190 degrees while in motion. In heavy stop and go traffic it can get to 190 or slightly over, but 190 is nothing and when moving again the temperature quickly drops back to normal. I would recommend sticking with your water pump as a “high flow” pump will mask but not correct the design flaw in the spacer. While there are a number of things that can contribute to our Y blocks overheating Chris’s spacer hits one right on the nose. I highly recommend it 🚗.

If he ever gets around to casting them in aluminum, I will order one.  In the meantime, the orig. CASCO modified pump I bought years ago solved all my overheating issues (and I run zero coolant pressure).