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Old 03-27-2011, 10:34 AM   #1
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Loosing water through coolant overflow

I have 10 year old boxster s which i have owned 4mths. Just discovered that even when filled to minimum level, the water level in my coolant tank rises (under pressure?) and flows out of the coolant tank overflow. Engine smells hot but gauge shows appx 85 rises to around 90 and fans kick in. just lost gallon of water in 20 miles. advice appreciated, Best! Glen

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Old 03-27-2011, 04:16 PM   #2
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you need to replace your coolant breather valve.

Changing the coolant breather valve
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Old 03-27-2011, 05:25 PM   #3
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Are you sure it's coming out of the over flow? There is a know problem with the tank cap, that leaks from the cap down the drain pipe. I your number on the cap is not 04 or higher , replace it. It's realy inexpensive
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Old 03-27-2011, 05:47 PM   #4
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Yeah, maybe the bleeder, maybe the cap. Can you see where the overflow is coming from? I'd start with a new cap and I'd take the 8 screws out and look at the bleeder valve top but I wouldn't replace it unless I saw something obvious. Also I'd fill the tank and bleed the system with the valve until the temp came up enough to run the fans. Then I'd close the bleeder and see what happens.

Do the radiators get hot? If not you'll need to fix that first, either air in the system, a bad water pump (the plastic impeller can break) or something else that is keeping the coolant from flowing. If the radiators get hot it probably something with the cap or valve. On my 2000 S (bought it in December) I replaced both the tank cap and the bleeder valve cap only to find my leak was actually coming from the o-rings under the bleeder valve housing, but mine wasn't leaking as much as yours so they might not be the same issue for you. Here are a couple of pictures of my bleeder valve and the o-rings in the event you find a need to go that far.

The bleeder valve cap after removing the 8 screws.

The bleeder valve housing under the cap. This piece lifts straight up but it's very tight and you'll need to wiggle it with some big pliers to get it loose. You can see my new pressure cap with the suffix "04" signifying the latest design revision.

Underneath are 2 o-rings. They are laying loose in the picture but in real life they fit over the respective openings. New ones fixed my leak.
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Old 03-27-2011, 06:57 PM   #5
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All the prev post are very sound advise....

If you check all the prev mentioned and the leakage is not solved... you will need to have a closer look at the coolant tank itself....

Mine was originally leaking at the O rings... but as I made the mistake (or fortune ?) of re-installing the valve a second time and probably used too much force the 2nd time around and ended up leaking at the coolant tank itself....

The leakage from the coolant tank can be very difficult to find... Mine was leaking below the breather valve and on close inspection, it looks like 3 little scratches on the plastic of top of the coolant tank... But leak it did (very very slowly and u can hear hissing everytime the temp reaches 85 degrees or so).

So... if you hear the hissing noise, don't assume it's the breather valve working... (I did and was wondering why it vented so early, until I saw drips of coolant bubbling from the bottom of the valve housing).

Last edited by shlim8; 03-27-2011 at 07:04 PM.
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Old 03-28-2011, 04:43 AM   #6
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the bleed valve is a $40 part. if you remove the old one to inspect it, just put a new one in.
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Old 07-16-2012, 04:43 PM   #7
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If the bleeder valve o-ring is bad, where will the leak show? around the bleeder valve or out the overflow tube?

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