Old Post but want to add to the statistics of this problem. My 1997 Boxster had a freeze plug let go. Supposedly Porsche used Non-aluminum freeze plugs in the 1997 engine block where it can corrode and rust away.
I do auto cross so I run straight water. Not knowing the freeze plug can corrode. The plug corroded and I would lose coolant with no external leaks. Only symptoms the loosing of coolant was very slow. Occasionally start to get hot when sitting in traffic.
One day on the freeway the plug let go. I get the coolant warning light. Pulled over and noticed the entire coolant tank was emptied. Thinking the expansion tank might have burped all the coolant out I added water to the tank, looked under the car for leaks, but there was none and I continue to drive. In less than a minute the coolant light was on again.
I was completely puzzled, did the coolant tank burp all the coolant out again? I added more water, but this time the water completely vanishes right away. Pulled the dip stick and its milk shake.
Completely destroyed this engine thanks to internal freeze plug by the cam shaft that corroded away.
Had less than 70,000 miles.
When you thought the IMS was a concern, this unsuspecting corroding freeze plug is catastrophic failure.
Sadly my 986 Boxster has been sitting in my garage since 2019. Contemplating on Tesla Large Unit conversion ~$65,000 or just rebuilding the 2.5L. Currently getting my fix with 981 Boxster S
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