Located directly on the cylinder head, a valve cover is a critical component that prevents oil from escaping from the top of an engine. Oil keeps temperatures down and reduces friction between moving metal components. That’s why any damage to your valve cover – which can result in an oil leak – can mean serious problems under the hood. Considering its importance, you might wonder why automakers have largely moved away from relying on metal. In some cases, the engine bay of a car has become a mess of plastic today, and this is because plastic is cheaper and lighter than traditional materials.
Ever since the 1970s, when the Energy Conservation and Policy Act ordered automakers to readily display fuel economy figures on window stickers, brands have been looking for ways to improve efficiency. At the same time, corporate average fuel economy standards were also introduced, essentially setting the bar for what automakers were required to provide in terms of miles per gallon to avoid fines. According to a report published on Springer, for every 10% reduction in a car’s weight, fuel economy improves by up to 8%. Replacing heavier metal parts with plastic helps vehicles shed pounds, and improves gas mileage.
While the automotive industry has eagerly entered the world of plastic as a substitute for metal, it is not the only industry making this change. Overall, moving from metal to plastic can provide a potential cost reduction of up to 50%, according to KAYSUN. This is because there are not as many stages involved in manufacturing plastic parts versus metal, essentially meaning more parts can be made faster.
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Metal valve covers are much more durable and perhaps look much better
Classic 426 Hemi Head V8 engine in a car – Kosoff/Shutterstock
Enormous strides have been made to make plastics stronger and more able to withstand the rigors of a hard-working engine. However, as they relate to valve covers, they present some issues. One of the problems with plastic is that it is more prone to flexing, bending, or twisting over time than metal. As mentioned before, the valve cover is basically the engine cover, which keeps its oil inside. Unfortunately, plastic valve covers can develop small cracks, which can sometimes be impossible to find without careful examination. These hairline cracks can even occur during routine maintenance. If you need to replace your gaskets, some mechanics simply recommend getting a new valve cover, as simply working to remove the old plastic one can cause damage, leading to oil leaks.
While it’s clear why automakers switched to plastic, some argue that those coatings detract from the look of an engine. When lifting the hood (especially on a vehicle with a more robust engine), being greeted with large plastic covers does not provide the same experience for enthusiasts compared to vintage models with metal components. Look at some of the best production machines ever made; while there are some exceptions, most aren’t sporting large chunks of plastic instead of metal. Granted, you can always follow guides on how to paint your valve cover to offer a better look regardless of the material.
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