Some people think that pressure caps don't wear. Some people say the Lotus OE radiators with plastic side caps are no good.

Every pressurized system needs a protection mechanism to prevent it from building up too much pressure. If the system builds up too much pressure (or even when the cap gets stuck) something has to go. The weakest part will be the plastic side caps, so they will blow. You can't really blaim that on the design of the radiator if you're not sure about the pressure in the system!

Our rule of thumb for a Coolant Resevoir Pressure Cap is two years. From there, it will either start to get loose (boiling, temperature going up manically) or it'll get stuck (radiator blowing).

Think about it, this cap is easy to replace, it's cheap. It simply is disaster prevention!