Many automotive engines now feature an array of “plastic” components (not merely plastic, but various polymer/composite formulations and constructions.) This is no secret. The move, from metals to composites, saves weight, something that automakers continually strive to accomplish in their ongoing quest for improved fuel economy.
The use of composite materials also provides a manufacturing cost savings, in terms of less costly injection molding as opposed to metals that require more extensive machining operations to achieve a finished product.
However, as we all know through the school of hard knocks, sometimes plastic components warp or crack due to thermal changes, age, stress or mishandling. One example is plastic thermostat housings/water necks, which sometimes warp at the base, preventing a seal; or they crack. Either problem can result in coolant leaks.
Another example is plastic molded intake manifolds. A case in point is the manifold for the Ford 4.6L engine, which is sometimes prone to cracking, allowing coolant to leak directly into a coil-on-plug well, migrating and causing an intermittent misfire. While plastics are lighter and won’t rust or corrode, they’re not impervious to wear and tear or just plain aging.
Whenever servicing an engine where composite components are found, be sure to inspect for signs of damage, especially warping or cracking. Even though such issues may or may not present a current problem, catching any concerns early can save headaches for both you and the customer.
“Plastics” have their use and are often wonderful alternatives to metals, but they’re not bullet-proof. Never assume that just because a part isn’t rusted or corroded that it’s good to go.
