1968 Dart cooling system & gauge Questions
Like Dana said there must be a small leak somewhere. Dont see any fluid leaks though
Keywords in what I wrote is "The other possibility..." I was not saying that you did have a leak and if you run your system like the OEM intended with a 1" air gap at the top of the tank you may never see a drop of fluid if it did have a leak. BUT I suspect its just the cap functioning as intended
You can have your cooling system pressure tested for leaks if you are worried.
I run a pressurized 16 lb cap because I don't want the coolant to ever get to the boiling point. I also run the 1" air gap in the top of the tank and I DO NOT have an overflow. I have not dropped a drop since 2017. I bracket raced the car once and got to the 3rd round. I had to have a catch can for coolant. I was assured I would puke out some coolant but NOT A DROP. Stock 7 blade fixed fan, stock no fan shroud, stock HD cooling Copper Brass radiator, 273 2bbl, automatic, 180 deg thermostat, 16 lb constant pressure rad cap.
The average person can blow between 1.5 and 3psi so the difference between 13 and 16 is nominal but the difference between 212 and 219 (9 additional degrees due to the lack of those 3 psi) is substantial
(AND yes I know the boiling point of coolant is much higher then the boiling point of water - numbers just used for the example)
That's where I have seen the REALLY good list of videos and booklets, Thanks Matt!