Losing coolant but oil is fine and no visible puddles
The fluid is escaping in a place that leaves no external trace, even when a pressure test confirms a rapid drop in PSI. Owners rule out the oil and replace accessible caps, but still see no puddles or bubbles when testing. This invisible drain leaves them unable to repair the system and struggling to find professionals willing to spend the time to properly locate it.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
Losing coolant but oil is fine and no visible puddles
- 1Replacing the radiator cap and coolant filler neck in hopes of a cheap fixDid this help you?
- 2Running a pressure test with soapy water to hunt for escaping air/fluidDid this help you?
- 3Pressurizing the system with dry nitrogen to observe pressure dropsDid this help you?
- 4Spraying soapy solutions on accessible connections to look for bubblesDid this help you?
- 5Putting UV dye in the refrigerant to find leaks with a UV lightDid this help you?
- 6Topping off the system with refrigerant and hoping it lasts the seasonDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Sprayed Big Blu all over the accessible refrigerant connections, brazed joints, service ports, reversing valve connections, and coil areas, no bubbles or foaming anywhere.”source ↗
“Right now I can’t justify $7,000 for a new pool heater that gets used 10 times a year and would REALLY like to find the leak to maybe get a few more seasons out of this heater.”source ↗
“am struggling to find someone willing (or able) to take the time to do a proper leak test.”source ↗
“I’ve refilled my coolant reservoir to F and in a month it was slowly dropped 1/4 way from L to F. Does anyone know where the heck the coolant could be going?”source ↗
“Oil looks good, no visible puddles, radiator cap and coolant filler neck was replaced.”source ↗
“I got a pressure test kit from Autozone, pumped it up to 15psi, and within a minute it dropped to 10psi. I kept pumping it back up and kept dropping. Wouldnt that suggest a MAJOR leak? I didn’t see any puddles during the test.”source ↗
Where this came up
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