Q: I discovered a leak in my car's coolant reservoir (radiator expansion tank) from a crack that has developed. Tank is plastic and temperatures where car is parked at nite are about 10 deg. F.
A: It depends, if the car is old and is subjected to extremes in temps, very cold, very hot, etc then yes, the plastic can degrade and develop a leak, I've seen this before on an old car that I had years ago