March 2

Plastic Engine Parts

Auto Repair, Car Costs, Cars and the Environment


While modern cars keep getting more reliable with many of the parts that once failed on a frequent basis no longer doing so, there is a new whole new group of part’s failures thanks to plastic. Plastics have come a long way and because of their light weight, moldability, low cost and durability they are used in many vehicle components. When comparing a 1960’s vehicle to a 2011 model the change under hood is phenomenal: under the old vehicle’s hood almost everything is metal while the new cars hood is 40 to 50% plastic.

While plastic is very durable it creates much of today’s repair and breakdown work. Some of the problems that we see are water pump impellers breaking, thermostat housings leaking, plastic pipes snapping and intake manifolds cracking. Frequently there are metal replacement parts available and that is what we use when available.

Which cars are prone to these concerns: a few that come to mind are VW, Audi, BMW and Jaguar water pumps; various Ford cars and trucks with plastic intake manifolds and plastic thermostat housings and  VW plastic thermostat housings. This is by no means an extensive list, there are many more.

The use of a plastic water pump impeller seems strange because, while the manufacturer is obviously saving weight, the part is so small and the cost of failure so high that it seems a silly trade off. Oh well, we don’t build the cars we just fix what comes along and to be positive (and somewhat cynical), the manufacturers have created work for us!

Water pump with broken plastic impeller
Water pump with broken plastic impeller

Plastic Intake Manifold
Plastic intake manifold: Ford 4.6L

About the author 

Bernie Pawlik

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