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boxsterd
I have a slow coolant leak on my '01 base and it's from the coolant reservoir tank.
Pull back the felt covering in the trunk, passenger side, and you can check for dampness yourself.
I seem to be adding about 1 gallon of coolant/distilled water mixture per month.
Based on my experience with my Boxster that could very well be a coolant cap leak.
With no signs of any leaks the low coolant level light came on. I added nearly a gallon of distilled water and brought the level up to where it should be.
I checked as best I could and found no signs of a leaking coolant tank. I removed the cap and cleaned it in the sink under hot water and then cleaned the tank threads to which the cap threads onto.
In around a month of almost daily use the light came on again. Still no leak sign but I kind of remember seeing some water condensation on the underside of the trunk lid or maybe on the rubber seal that circles the fluid service bay.
On a hunch I used aluminum foil to tent the bay with the engine up to temperature and in a few minutes there were drops of water on the foil. On another hunch I bought a new cap. Leak solved.
The coolant tenk did eventually leak but in my car's case it never leaked enough to drop the level enough to cause the low level warning light to come on.
The only real sign I got of a coolant tank leak was an odor of anti-freeze once in a while when the engine was up to temperature.
I kind of found the coolant tank leak by accident. A test to confirm both radiators were running when the coolant got too hot turned into a "hot" coolant pressure test which after just a few moments after shutting off the hot engine when the fans were running had hot coolant gushing out of what proved to be the bottom of the coolant tank.
To show you how the lack of heat and pressure can have the tank leak heal itself, I let the car cool down over night then the next morning using distilled water brought the coolant level back up to where it should be. Seeing no signs of leaks under the car I started the engine and drove it a couple of miles to the dealer. At no time did the coolant leak and at the dealer even after I parked the car no leak sign appeared.
In the case of your car regardless of the leak source you need to find it and fix it. The inability of the system to hold pressure can result in localized overheatring which can cause collateral damage to the engine. A seemingly live with it leak can be an engine killer if the leak results in a cracked head. Wtih these older cars a few thousand dollar repair bill can be the last straw and results in the car being lost.