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Boxster Recurring Coolant Dump Problem

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I have a 2002 Boxster that enjoys dumping the entire contents of the engine coolant on a regular basis. The entire coolant tank seems to be dumped from the emergency overflow whenever this happens.  No warning lights appear on the dash either before or after this occurs.  


The dump happens only when I turn the engine off after driving.  After turning the engine off I hear rapid running liquid coming out of the back of the car, and can see the coolant fluid flooding over the pavement.  It completely empties the tank and takes about 30 seconds.  


There does not appear to be a leak in the system.  The first time it happened I called roadside assistance they pressure tested the tank without issue.  I subsequently took it to a garage which also pressure tested the tank and did not find an issue.  The level does not gradually decline: it is either fine or it dumps the whole thing on power-down.


A few months ago the car started dumping the coolant very frequently (almost every time I drove).  I took it back to the garage which decided to replace the coolant overflow reservoir which apparently had a crack.  This seemed to improve the situation, but in the last few weeks the problem has returned and the coolant is dumped after most trips when I turn-off the engine.


The engine temperature shown on the dash is normal, no warning-lights come on, and the fans work normally.  At least one of the times this has happened in the past I did not notice it immediately and ended up driving around for some time before realising there was no coolant.  


I have owned the car for about 2 years, and the issue first occurred about a year ago.


Has anyone come across this before?  I don't really want to take the car back to the garage for them to do yet another random "fix", charge me a fortune and not actually address the problem.  

Edited by DrivingQuant

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Welcome to RennTech :welcome:


This is obviously not normal behavior.  When all this work was being done on the car, did they refill the system using the recommended vacuum filling system, or did they just fill and "burp" it?


Reason I ask is that we often see cars with air pockets in the cooling system behaving this way.

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Agree with JFP, make sure system is properly bled. On that note, have had a problem with the bleeder valve and older version reservoir caps that both caused coolant leaks.

I've also had some similar issues and it was the heater valve causing problems. Pn 928-574-573-03. I'm not suggesting you throw parts at it though. Just my experience.

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If the part number on your coolant reservoir cap does not end in 04, then replacing it with one that does might be a start to narrowing down the problem.

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I am having issues with my heater warming up. I have changed the thermostat and flushed the system. All signs are pointing to a heater valve but I can't find its location on my 97 Boxster. Any ideas or diagrams you can refer me to? Thanks in advance.

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You have the PET available for free here. Move down on the page and enter your model type "Boxster" and year "1997-2004" and it will offer a download of the parts manual with cut away diagrams.

Edited by mikefocke

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Same problem.  Mine was a faulty coolant cap.  If its a steady stream from the right rear area there is a good chance this is your issue

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I had a similar problem with my 02 boxster, turned out to be the O ring in the bleeder valve on the reseviour. I found out when I took the cover of the reseviour off, drove around, and parked it. When it started dripping on the ground I looked and saw it was from there. Dealership had the 2 o rings (one big, one small) for less than $4. Took it apart and turns out that the big O ring was tightened so much it ripped. Replaced and drove fine for a year. Leak happened again and it was the same o ring. This time I put a thin layer of silicone on it and it's been fine ever since!

Sent from my iPhone using Tapatalk

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