Home › Forums › Stay Dirty Lounge › Service and Repair Questions Answered Here › Coolant pressure tester "adapter" › Reply To: Coolant pressure tester "adapter" May 25, 2021 at 3:06 pm #990706 Richard KirshyParticipant My guess: It is for the purpose of testing your radiator cap. This reply was modified 2 years, 4 months ago by Richard Kirshy.