Why are valve covers made of plastic if they warp?

Question

I just brought my 2016 Honda CRV into the mechanic for an oil change and transmission fluid flush. The mechanic did some other checks and told me that my valve cover has warped and needs to be replaced. I asked some questions (I don't remember everything I asked) and he said the cover is plastic. He also said all other car manufacturers do the same too; make their valve covers out of plastic.

I'm wondering why the cover is made of plastic if heat will warp it. I'm not a car enthusiast but the only reason I can think of to make it plastic is weight. However, couldn't the car companies use aluminum or some other light weight metal to make the cover out of? I assume aluminum is less likely to be warped due to heat than plastic.

Answer 1

While the valve cover is technically "plastic", it's actually a polymer which stands up to heat pretty well. While they don't usually warp, they can warp depending on how hot they get. Why do most car manufacturers make them this way? The absolute answer is cost. You can injection mold a 100 (or more) of them in the time it would take you to machine an aluminum valve cover. The material is cheaper than metal and a lot easier to work with.