[Yellow Noodle]

I recently replaced my radiator as a decently long crack appeared across the top of the old one. The car never overheated or got close to being hot. I checked the oil and there are no symptoms of a head gasket going bad. Temperature also stays steady when at optimum temp so I'm guessing the thermostat is fine. Just wondering what the cause of this could be? Someone I know thinks there may be a pressure buildup that caused the crack. Is it simply because it's a 17 year old part? I replaced it with a mishimoto radiator and would rather that not crack due to "pressure buildup" aswell.

 

[The_Evenger]

The plastic radiators will fail over time, there's no way to avoid it. I had one fail the same way and replaced it with an all aluminum eBay knock off as well. Never had any issues since.

 

[chase206]

Common issue with radiators bursting/cracking is caused by a faulty radiator cap. The cap is designed to release pressure at a specific PSI to the overflow tank. As the motor heats up, fluids expand and cause pressure in the cooling system to increase. If that pressure has nowhere to go it will break the radiator. Same thing happened to me a few years ago so I bought the ebay Mishimoto knockoff radiator made by DNA Motoring and bought a new OEM radiator cap. Never had a problem since then.

 

[Charlie-III]

Age is the main reason for "composite radiators" (plastic tanks and aluminum core) to crack. The plastic gets brittle over time with hot coolant inside.
Yes, excessive pressure could do it, but a low cause for cracking.