7 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHBig Coolant Loss Unexplained
Leading reported evidence
Fill expansion tank
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
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Discussions that performed work without a confirmed outcome
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Performed · outcome unconfirmed · Original poster
Took a chance and filled the expansion tank with distilled water while the car was running.
Leading evidence: 'Fill expansion tank' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check until the next day' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
Everything was too hot to poke around with so I couldn't check until the next day.
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Suggestion · Original poster
I know hoses, clamps and pumps don't self repair after this volume of fluid loss.
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Suggestion
I had a similar thing happen after replacing my coolant tank driving on a hot summer day for hours.
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Suggestion
I would run the car very close to your house up to temp and see what happens.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
7 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T133652Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Drove my 2002 996 with 75k to the store. Temp was normal, I parked and got out of the car to watch a quart of coolant gush out of the left rear area near the expansion tank. No hissing, no steam just heard glug glug as I watched and heard the coolant drain from the expansion tank. Took a chance and filled the expansion tank with distilled water while the car was running. NO LEAK. Still normal temp. Drove 20 minutes home, perfect temp, no leak. Parked in garage overnight, not a drop on the floor. Expansion tank still at full level. Could I have had a one time expansion tank pressure relief valve failure that self corrected after pressure normalized? I know hoses, clamps and pumps don't self repair after this volume of fluid loss. Does anything? Any thoughts? Tests?
The pressure relief on the coolant system is the cap. Maybe the cap wasn't tight and by filling up the system you got the cap on tight? Is your cap blue and ending with a part number 04? The old style black caps were updated several times over for simply this reason.
Thanks for responding. The cap has been untouched for at least a year, The cap is blue and ends in 001. I watched the coolant flow from the bottom of the engine somewhere and watched the air gulping inside the expansion tank as it puked at the bottom. Nothing came out at the top near the cap (if that matters). If a new cap is the fix for this exact problem can I get an amen and thank you again!
A leaky cap will most often generate steam (as well as liquid) because the caps leak when the pressure in the tank overcomes cap's ability to keep the coolant in. Unless the cap was really really loose, I doubt a leak out of the cap would cause glug glug. But hey, there's no other explanation I can think of, either. I would run the car very close to your house up to temp and see what happens. The tank could look full to you, but not up to the level where the leak is, either.
It could be the coolant tank. Some hairline cracks only open when there is a lot of pressure. I recently had a similar experience. Everything was too hot to poke around with so I couldn't check until the next day. The bottom of the tank towards the front of the car was still wet. It doesn't leak unless I take it on a fairly long/aggressive drive.I have a new tank on order.
I had a similar thing happen after replacing my coolant tank driving on a hot summer day for hours. It puked out coolant after shutting off the engine to refuel.
After quite a bit of investigation it turned out that it was an air bubble in the system.
A possibility for you?
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