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Discussion summary
YOUR RESEARCH996 Dumped Coolant? Twice.
Leading reported evidence
Replace cap too
Performed · outcome unconfirmed
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Read evidence and context
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Performed · outcome unconfirmed
I replaced my cap too with a new one, although I did have the blue updated cap already.
Leading evidence: 'Replace cap too' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check top of the tank' (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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Performed · outcome unconfirmed
Once removed and replaced with a new tank, I was determined to finding out where the leak was on the old tank.
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Suggestion
Check the top of the tank near the cap to see if it's wet or has a white residue.
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Suggestion · Original poster
I pressurized to 18 psi and everything held just fine, but if it basically only leaks under normal operating conditions and not under a normal pressure test, is replacing the tank my only option?
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I am somewhat mechanically inclined, but new to Porsche ownership. Looking for tips and suggestions on where to start with this issue.
I was sitting in traffic when my �01 996 dumped (purged?) a lot of coolant. Seemed like maybe a half gallon or so. Temps were still ok and traffic was stop and go, so I shut off the engine. I had to shut off and restart maybe 4 times before traffic started moving and I nursed it back home just 7 minutes away. As soon as I pulled into my garage, it dumped a bunch more coolant, about the same amount as before. Both occasions lost coolant from the rear, near or around the reservoir. As far as I can tell, there are no leaks, so it seems like it just built up too much pressure and then blew it off.
Where should I begin? Pressure test?
Yep, always start with pressure testing the cap first, then the system..
The cap should hold up 19psi then release down to 14psi then hold.....If it doesn't it can release/dump coolent as soon as the pressure start to rise...
That's how my cracked coolant reservoir behaved. The crack was not visible and couldn't be felt. The genuine Porsche tanks are insanely expensive for MK-I cars, but it's the only way to go, unless you want to do the job again every year or so. Trust me, you don't. Check the top of the tank near the cap to see if it's wet or has a white residue. That might indicate that the cap is bad or not the recommended one. But based on what you described I'm guessing its the tank.
My car arrived with low coolant, which I was unaware of. Drove around like that for 3 months and than put distilled water in my tank, was good for a week and than back below the min level. I had a crack and it finally broke and dumped the coolant all over the left exhaust side. Had it towed to the shop and yup it was a crack in the plastic tank, replace it asap
My car dumped coolant after losing a few ounces every season.
I changed the coolant tank - all good.
Once removed and replaced with a new tank, I was determined to finding out where the leak was on the old tank. I had to pressure the old tank with over 30 psi of air before I noticed a quarter inch crack close to the seam.
My guess, your tank is cracked, but only leaks under pressure AND when the plastic get hot from coolant and exhaust.
Pressurized the reservoir, and it is holding pressure just fine. I don't have the right adapter for the cap, but it is the blue one. Do you know what size I need or where to get an adapter? I am guessing it would be cheaper to just buy a new cap, but then I am risking dumping a bunch of coolant again if it is a different problem...
I was feeling ok about my tank until this comment. I pressurized to 18 psi and everything held just fine, but if it basically only leaks under normal operating conditions and not under a normal pressure test, is replacing the tank my only option?
Could this problem arise from a bad thermostat or water pump?
I rarely drive my car unfortunately.
I purchased my car in November 2018 - went in right away for IMS solution, clutch, flywheel, RMS, AOS, water pump/thermostat. Car had 45000 miles on it. In July 2022, it was a hot day (90*), went to a Porsche event, took a drive by Drake's house and stopped for a coffee. After the coffee, I went out to car and saw the coolant puddle. I never saw a drop of coolant before this. Prior to this, I would add a couple ounces of coolant annually. My car is parked on a lift so a coolant drop would be very noticeable.
I replaced my coolant tank (
Starting Coolant Tank Replacement 996.2 C2 - Rennlist - Porsche Discussion Forums
) Now I never add any coolant, no more coolant drop. So, my guess is that it is your coolant tank. Only way to know for sure is to remove tank and inspect. At that point, might as well replace it. I think yours is a C1, so the coolant tank is way more expensive unfortunately.
I would doubt that it is your water pump or thermostat. I replaced my cap too with a new one, although I did have the blue updated cap already.
My parts came directly from the Porsche dealer - yes expensive.
Just a bit of information. Genuine Porsche tanks don't come with a cap, you have to purchase that separately. If you get a tank that comes with a tank, it's not Genuine Porsche. I paid for a Genuine Porsche tank from AutoHaus AZ but they sent me an aftermarket tank that came with a black cap. Don't fall for that.
The part number is what's important on the top of the cap. If it does not end in 04, replace it regardless of color. My sister-in-law has a blue cap with the old part number and design. And yes, she just replaced it with the 04. Both are blue.
Originally posted "temps where still ok" not sure exactly what that means would be good to know an actual temp reading from temp gauge I mean it had to be some what elevated in order to purge coolant...no
I do not agree with this statement. The 996 and most modern cooling systems are closed systems. They will only dump coolant through the coolant cap or, if something like the expansion tank is compromised.
Cooling system is pressurized to stop the coolant from boiling - every PSI increases boiling point by 3* and a pressurized cooling systems ensures batter contact with coolant.
Although this car dumped coolant, the cooling system still remained under pressure hence why no real increase in pressure.
When I dumped coolant, I drove 45 minutes home. Temp gauge remained normal AND it didn't dump coolant again.
