Quote:
I will rent a pressure tester.
I didn't see this in time to offer a possible easier solution, You can buy a "tank valve" from Oreillys for less that $3 out the door & screw it into the cooling sender 1/8 NPT port & with an air chuck with shop air & a tire psi gauge pump the system up to 10 & see where it leaks from if external (hopefully not internal).

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live every 24 hour block of time like it's your last day on earth