Plastic Radiator Fill on 2001 Aurora 4.0 bursts

My 2001 Aurora 4.0 has a plastic fill box which is under pressure and where you add antifreeze. The other day I smelled antifreeze, opened the hood and found a hole the size of a bullet in the back middle of the box and antifreeze was pouring out. I was able to replace the unit and am back in business. I am wondering if I had a defect in the box, or is there some sort of soft plug design to force this to happen if pressure builds up. As you look at the new box, there is no noticible spot from the top which would indicate some sort of a soft plug, but perhaps it is from inside. Or, was it just a defect in the old box. I would question that, as I have put 92,000 miles on the car since new.

Finally, since that happened, it always says "low coolant", and now suddenly the "check gas cap" alert is also on. I can't reset them permantly. Also, check engine light is on.

Any ideas?

Thanks

Andy

double check to make sure you have reconnected the coolant level sensor to the harness with out that plugged in or fully plugged in it will tell you low coolant and if the check gas cap warning came on instantly when you changed out the tank i find that quite odd but it could be time for a new vented gas cap....

Thanks for your response. These things are such fun! After running for a couple of weeks, the low coolant went out, the gas cap message as well. Even the check engine light went out.

This week, they both came back on. Someone mentioned that I might need to bleed the antifreeze line, which I was going to do, but it went out. I try that, and also what you have suggested and will let you know what happens.

Again, thanks for your reply.