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‘02 Boxster S loss of coolant. Reservoir replaced, new cap, continues to loose coolant. No puddles.

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02 986 S. Replaced coolant reservoir due to age and stripped threads 6 months ago. Loosing coolant at about a quart every 200 miles.

No puddles noticed, car will occasionally heat up and discharge steam. Have bled the cooling system, however I am not certain that I have it completely bled. Puzzled!

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Thanks for the response.
The steam is coming from the right rear wheel well. When I replaced the coolant reservoir (OEM $400+ !!!), I replaced all of the coolant hoses as well as the transmission coolant valve.
There are no obvious leaks and oil is clean. No loss of power.

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The first thing I would do is a coolant system pressure test to see if the system hold pressure over time (15-30 min.).  If it does not hold pressure, your problem may lie deeper in the engine.


If it does hold pressure, I would do cooling system atmosphere evacuation, basically pulling a vacuum on the cooling system to see if there are any air pockets trapped in the system.  If there are, recharge the cooling system under vacuum and you should be good to go.

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1 minute ago, Slainte336 said:

Thanks, I will do just that. I followed (religiously) the process for bleeding out air pockets, but it is likely that without pressure testing, one is never certain.

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Manually bleeding out these cooling systems is a best a band aid which often does not work completely, we only refill these system under vacuum using the factory Airlift system.

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Had the same issue with my 1999 which also had a new tank. After doing a pressure test on the cap, found it was defective which was the reason for the steam discharge.

Bleeding the tank properly took me about 8 - 10 hours. After replacing the cap, and properly bleeding the system my problem was solved.

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