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Discussion summary
YOUR RESEARCHPossible cause of split coolant tank?
Leading reported evidence
Check coolant level without removing the blue top and noticed
Performed · outcome unconfirmed
No successful repair reported for this finding.
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0
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1
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Read evidence and context
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Performed · outcome unconfirmed · Original poster
The reason I ask this question is after completing a spirited drive today (which brought the coolant temp to about 190F) I checked my coolant level without removing the blue top and noticed that the relief valve was then in the open position.
Leading evidence: 'Check coolant level without removing the blue top and noticed' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'design fault or stress or the combination of both' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check coolant level without removing the blue top and noticed' (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
Just replaced my coolant tank due to leaking on a '99 996.
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Performed · outcome unconfirmed
Replaced expansion tank which had small split down the side.
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Performed · outcome unconfirmed
Given my experiences with both brands and my 996, I think I've replaced four tanks in the past 6-7 years.
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Discussions that suspect a cause
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Suspected cause
If it leaks after a long service life it is due to a design fault or stress or the combination of both.
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Check coolant level without removing the blue top and noticed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
The reason I ask this question is after completing a spirited drive today (which brought the coolant temp to about 190F) I checked my coolant level without removing the blue top and noticed that the relief valve was then in the open position.
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.
18 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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I have read that many times the coolant tank can split requiring a new tank and cap installment. Could this be caused by the pressure relief valve on the top of the tank, not lifting at high temps and the pressure consequently splitting the white plastic tank???. In other words the tank having a faulty relief valve? The reason I ask this question is after completing a spirited drive today (which brought the coolant temp to about 190F) I checked my coolant level without removing the blue top and noticed that the relief valve was then in the open position. Has anyone else noticed this happening to their car? I tried to close it but it went back up again to the open position.
where did it dump it from? What part of the sytem?
I just went into the garage and tried again and it went down and stayed down 20 mins after I arrived home. So my question remains:- if a valve (berp weir) is stuck down for some reason, would that be enough to split a plastic tank? I think just maybe... If so, then its worth us checking that the blurp weir is working correctly. Yes? It would appear that mine is.
I was not aware that it lifted on its own. This thread on 986forum suggests that this is not normal:
http://986forum.com/forums/general-d...olant-hot.html
Unless the car is so hot that the coolant is boiling, the system should not leak, and coolant levels should be consistent unless one of the know suspects (radiator cap, water pump shaft bearing, coolant tank) are misbehaving.
The 996 cool tanks are known to need replacing,its one of the known issues with the 996 series. At some point they wear out(crack or split) and start to leak.you will notice this way before it becomes a real problem.mine lasted 76.000 miles. Just part of maintaining the car in my view.
. Plastic generally does not wear out, at least in several lifetimes. I believe the tank is made of polypropylene or nylon. If it leaks after a long service life it is due to a design fault or stress or the combination of both. Where do they develop a leak at most of the time? Reason for the question is I have a tiny bit of pink coolant under my C4S.
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The burp weir thingy on mine too is up whenever I drive and get the engine to operating temp. Interesting to know if this is normal. I paid attention to this sometime ago in relationship with burping the coolant system with coolant change. It says to position the metal tab so that the pressure relief valve is in open/up position to burp the system of air. It's a head scratcher for me because mine is always in open position whenever I drive. Btw, I haven't change my coolant yet.
Some are talking 986 and Boxsters. I have the 996 car which has the plain white tank with blue cap which looks nothing like the boxster. At least not the photo I saw on the link. Maybe the pop up valve only lets out pressure and not the coolant. Could be a non return type valve. However, if the cap was not on properly or damaged then the water when at high enough temps expands and would get out that way. Around the side of the cap. If the cap was good and the valve was not lifting because that was bad, then the pressure built in the system had no where to go only to crack the weakest part of the system -; ie the plastic tank. That makes sense to me.
The "burp" valve goes up when there is pressure (heat) in the system. This is normal. It does not release pressure, it is not meant to release pressure.
The valve in the removable blue cap (hopefully -04 or newer part suffix) releases the pressure..
The burp valve, when the is bail manually snapped up, is to break the vacuum allowing air bubbles in the system to escape, IE migrate to the tank, when the engine cools off.
As far as tanks failing. Look at what lives below the tank. A HOT muffler that cooks the tank making it brittle. That is why older tanks look yellow. I think that is also one of the reasons Porsche put the engine fan near the tank. When the engine fan comes on it blows cool air into the engine compartment at the tank.
no arguments here
Which why the recommendation to replace the tank/cap/pump/t-stat around every 60K miles as a preventive measure is a good idea for me.
Small amounts of coolant, especially on the passenger side of the engine (US) can also be the coolant O-rings in the oil cooler. Also common failure items, and potentially worse than a leaking coolant tank.
FWIW, coolant tanks are also a common problem, the leaks that is, with BMWs and Mercedes. Given my experiences with both brands and my 996, I think I've replaced four tanks in the past 6-7 years. Geez...what's so hard about manu'ing a long life plastic tank?
relinuca
IIRC the pressure relief is in the cap.
The tank fails because of material fatigue and based on my second hand info along the bottom seam. This is a weak point.
There is no conspiracy.
The tank (indeed the entire cooling system) wants to maintain pressure for it is the pressure that keeps the coolant from boiling.
If the valve on top of the tank is open that's a problem.
BTW, 190F is not hot... The fans on my Boxster do not even turn on until the coolant temp reaches 212F and do not switch to high speed until the temp reaches 216F. I've seen the coolant temperature reach 226F and stay there, once in southern AZ in 116F ambient heat and another time more recently -- last summer -- when pushing the car hard in the twisties on a 90F day.
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