Coolant Expansion Leak - OK to Drive?

[911monty]

Originally Posted by xhifer

Right after I gave the 986 to a family member to drive 800 miles home, he told me the coolant temp light was blinking.

After diagnosing it, it seems like there is a small crack on the seams between the black and clear plastic part of the coolant expansion tank.

If I keep the coolant level below the Low line, nothing leaks out, but when I refill it to the Full mark, coolant would leak out of the crack and then settle at below the Low mark after the car cools down completely.

He wants to just drive it home and take his time to fix it. I think he should be fine since it's essentially like driving with the coolant bleeder valve open right? Or am I completely wrong?

Absolutely not! The tank will not hold pressure with a crack. There needs to be pressure in the system to prevent localized hot spots in the water jackets that will boil forming vapor and preventing proper heat transfer especially along cylinder jackets and heads.

Oh and do not use an aftermarket to replace, that is a common problem area even with the OEM German tank.

And to answer about the bleeder. The bleeder does not vent to atmosphere. It is a high point bleed from the front radiators and the oil cooler to eliminate air in the system.