Plastic for cooling sucks.

My daughter's 2007 Taurus has the tank with the rad cap on it.

For some reason the plastic started to desintargrate in one spot, like what happens to plastic that has been in the sun for 50 years. It was about 1/2 as thick as the rest of the plastic.
Rather then wait till it blows I replaced the tank.
My 2002 Taurus has the plastic expansion tank too, so far it's in good shape.