It is also possible crud has built up on the back side of your number 6 cylinder. This is pretty common. It can be helped, but it takes some work and you'll probably have to remove your water pump. Sadly you can't buy the chemicals that used to dissolve this stuff very well any longer. I would suggest opening the drain cock at the far rear of your engine (manifold side) to see if anything runs out there. If it doesn't, you're plugged up. If you have the original mechanical temperature gauge, it will be located at the rear part of the head and this is where the heat from that sort of situation will be located (at the rear of the engine). Occasionally you can remove the drain cock at the rear of the engine and work a straightened coat hanger with a small hook bent into it up and behind the number 6 cylinder to get the engine to drain. Sometimes you just won't be able to solve a lot of this problem with, though. I have managed to get all the coolant out of the block and then remove the water pump and fill the block up to the water pump opening bottom line with CLR and let it sit overnight. You can also make a strong solution of citric acid. You would drain either of these out the rear hole where the drain cock was and repeat every day for about a week. The fact you had no thermostat suggests to me a prior owner was trying to keep the engine cooler because he had the same problem. In a perfect situation, you'd remove the engine, remove the large access piece at the back and clean it that way, but this isn't always convenient. Good luck.
Edit...also the 1/8 inch hole you've heard about (actually most folks use a slightly smaller drill bit) is a "burp" hole. It allows air to escape preventing a trapped pocket which will also make your engine run hot. But most thermostats are now built this way or they have a "jiggle pin" which does the same thing.
Last edited by Jon G; 12/02/2025 12:52 AM. Reason: forgot to answer
