How to identify a mystery liquid leaked inside my car
Unknown puddles or fluid spray inside a vehicle cabin often stem from failing heater cores, clogged A/C evaporator drains, or compromised power steering lines. These leaks leave car owners trying to identify strange colored fluids to anticipate expensive repair bills and avoid unnecessary mechanic visits.
What the numbers show
Counted from the threads quoted below. How we count
- Most of it landed at once — the busiest month was September 2026, with 6 people.
- This comes up 9.1× more often in r/MechanicAdvice than across the site as a whole.
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.
- 1Using Lysol wipes and soapy water to clean the affected interior surfacesDid this help you?
- 2Crawling under the vehicle to visually inspect the leak sourceDid this help you?
- 3Bringing the vehicle to a professional mechanic for diagnosisDid this help you?
- 4Waiting until the mechanic reopens to get a professional diagnosisDid this help you?
- 5Turn off the AC and let the car run to see if the dripping stopsDid this help you?
- 6Searching online for symptomsDid this help you?
- 7Power washing the engine bayDid this help you?
- 8Asking mechanics or online communities to identify the substanceDid this help you?
- 9Inspecting vehicle parts like hinges and pipes for leaks or lubricant applicationDid this help you?
- 10Replacing components like the water pump, thermostat, and thermostat housingDid this help you?
- 11Flushing and changing the coolantDid this help you?
- 12Continually topping off lost fluid with deionized waterDid this help you?
- 13Guessing it might be rainwater, AC condensation, or wiper fluidDid 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.
“When my gf and I went to her car this morning we found this odd orange liquid in the interior.”source ↗
“Any idea what kind of fluid this is?”source ↗
“Does this look like oil or rust in the cooling system? I have had the coolant changed when i replaced the water pump and the reservoir looks the same.”source ↗
“noticed a leak from what looks like the transaxle? The fluid looks dark brown no leaks appeared from above. Any idea what it could be is it still safe to drive?”source ↗
“I just noticed what I believe to be coolant (possible power steering fluid?) leaking from the front passenger side of my JKU.”source ↗
“Crawled under and found this plastic hose to be the source of the leak.”source ↗
“I’d like to research a bit before bringing it in and know what I’m in for for possible replacement costs.”source ↗
“1985 Opel Rekord, just bought a few days ago. Drove fine before this. Did a quick Google search and it looks like it could be water trapped somewhere?”source ↗
“I have a Toyota Yaris 2014 automatic. Today I've noticed this white stuff on both doors, drivers side and front passenger side.”source ↗
“Is this the black pipe leaking or some tube that has burst? I can't think of anything else that could have caused this.”source ↗
“It’s a 2007 honda civic . The liquid is clear and doesn’t smell”source ↗
“ok thx , My ac has been broken for a while and just got it fixed so I’m just seeing this now”source ↗
“No clue what type of fluid this might be hopefully it’s just rainwater but it’s been leaking even after a 30 minute drive.”source ↗
“Leaking from couple spots of the undercarriage but it does seem to be water or wiper fluid since i have noticed my wiper fluid goes quick as well”source ↗