[XutvJet]

In most cases, no, it's not a problem. Plastic these days is pretty robust. Though, there are some parts that shouldn't be plastic, especially those in high heat, high stress areas, and/or not easily accessible areas. Engineers should know better.

The old mechanics that bitch about this stuff and talk about the glory days of when everything was "metal" seem to forget that cars back in the 50s, 60s, and 70s were generally looked upon as disposable. People bought new cars every 1 to 5 years and most cars rusted out within 7-8 years if they lived in an area with salt treated roads. In general, people own their cars far longer longer and cars in stay on the road longer as well. Cars are also far more reliable than they've ever been, all things considered.

I have little sympathy when people bitch that their 10+ year old car has developed a rash of issues. Stuff wears out over time, regardless of mileage. The reality is people have gotten used to how reliable their cars are and tend to loose their mind when they actually have to make some repairs. Cooling systems, regardless if they are metal, plastic, rubber, etc. are under a ton of stress. It's not odd that a lot of cooling system parts may need to be replaced at 10-15 years. No manufacturer is immune to this. It was like this in the 1950-1990s too.