For years, vehicle manufacturers have been replacing parts that were traditionally made from metal with plastic and composite components.
Thermostat housings. Water pump assemblies. Coolant flanges. Oil filter housings. Valve covers. Intake components. Fittings, pipes and connectors.
And after repairing these vehicles every day, we have formed a pretty strong opinion about it:
When the same component can reasonably be made from either metal or plastic, we believe metal is the superior material for long-term durability.
That doesn't mean every plastic component on a vehicle needs to be made from metal. Modern plastics have their place, and there are plenty of applications where they work perfectly well.
But when you're talking about components exposed to engine heat, cooling-system pressure, vibration, oil, chemicals and thousands of heating and cooling cycles, we would rather see a quality metal component every time.
And increasingly, the repair industry is proving why.
Why Are Manufacturers Using Plastic?
There are several reasons.
Plastic is lighter.
It's less expensive to manufacture.
It can be moulded into complicated shapes that may otherwise require several metal components to manufacture.
Most importantly, manufacturers are under enormous pressure to make vehicles lighter and more efficient in order to meet increasingly strict fuel economy and emissions requirements.
Every little bit of weight matters.
Saving a few hundred grams on one component might not sound important, but multiply those savings across hundreds of components and millions of vehicles and it becomes significant.
From the manufacturer's point of view, it makes sense.
From the vehicle owner's point of view 8, 10 or 15 years later, it can be a very different story.
Our Opinion: Durability Is Being Sacrificed
This is where we believe the industry has gone too far.
We believe manufacturers know there is a durability tradeoff when some of these components are changed from metal to plastic.
They're designing vehicles to meet emissions, fuel-economy, weight and manufacturing-cost targets.
Long-term durability is only one part of that equation.
And unfortunately, the person who eventually pays for that compromise isn't usually the manufacturer.
It's the vehicle owner.
A plastic cooling-system housing can perform perfectly for years.
Then repeated heat cycles make the material brittle.
A hose connection cracks.
A sealing surface warps.
A fitting snaps off.
Suddenly a relatively inexpensive piece of plastic can result in hundreds or thousands of dollars in repair costs because of where the component is located and how much labour is required to replace it.
We see it all the time.
Metal Is Simply a Better Material for Many of These Applications
Again, we're not saying plastic should disappear from automobiles.
But if you gave us two otherwise identical parts — one made from a quality engineered plastic and one properly manufactured from aluminum or another suitable metal — we're choosing the metal component for long-term durability.
Metal generally handles heat, pressure and repeated temperature cycling better.
It doesn't become brittle in the same way an aging plastic housing can.
Threads are generally stronger.
Hose connections are harder to snap.
Flanges are less prone to cracking.
And when the part is buried underneath an intake manifold or requires hours of labour to access, that matters.
The cost of the component is often the smallest part of the repair.
The Aftermarket Has Been Fixing This Problem for Years
The aftermarket recognized this a long time ago.
For many common vehicle problems, aftermarket manufacturers began producing metal replacements for plastic factory components.
We've seen aluminum thermostat housings replace plastic housings.
Metal coolant fittings replace plastic ones.
Upgraded aluminum oil filter housings replace plastic assemblies.
Metal water pump components replace plastic versions.
And when there's a proven, high-quality metal upgrade available, we generally recommend it.
Why install the same design that just failed when there is a better option available?
Our goal isn't simply to get the vehicle out the door.
We want the repair to last.
Now the Vehicle Manufacturers Are Doing It Too
This is the part that really gets our attention.
We're now seeing situations where the vehicle manufacturer originally installed a plastic component — but the replacement or updated component they supply later is made from metal.
Think about what that tells you.
The vehicle was originally engineered with a lightweight plastic component when weight, emissions and production cost were major considerations.
Years later, when that component needs replacement, suddenly a heavier and more durable metal version is acceptable.
In our opinion, that's pretty telling.
Manufacturers understand material properties just as well as anyone.
They know metal is more durable in many of these applications.
We believe they're making a calculated compromise when the vehicle is manufactured: save weight, meet efficiency and emissions targets, control manufacturing costs and accept that some components may not last as long as they would if they were made from metal.
Then, once the vehicle is already on the road and the original component fails, those same restrictions aren't nearly as important.
And now a metal replacement can become the solution.
The unfortunate part is that the customer gets to pay for the upgrade.
The Mercedes Example ---Facebook Video Link---
The Mercedes technician in the video we're sharing demonstrates exactly why this subject has become so frustrating for people in the automotive repair industry.
You can have a component originally manufactured from plastic, and when the repair becomes necessary, there's now a much more substantial metal solution available.
From our perspective, it raises an obvious question:
If metal is good enough to be the improved replacement, why wasn't it good enough when the vehicle was built?
We think vehicle owners are justified in asking that question.
Manufacturers Have Different Priorities Than Vehicle Owners
Vehicle manufacturers have an incredibly difficult job.
They need to meet safety regulations, emissions standards, fuel-economy requirements, production targets, warranty expectations and a price point customers are willing to pay.
We understand that.
But the manufacturer's priorities when producing a new vehicle aren't necessarily the same priorities you have when you want to keep that vehicle reliable for 10 or 15 years.
The manufacturer benefits from saving weight and production costs.
The owner benefits from durability.
Sometimes those goals conflict.
And we believe the increasing use of plastic in high-temperature, high-stress engine components is one of the clearest examples of that compromise.
What We Recommend at POCO NAPA AUTOPRO
When we're repairing one of these components, we don't simply look for the cheapest replacement.
We look at why it failed.
We look for updated designs.
We look at the quality of the available parts.
And when there is a reputable metal upgrade available for a known plastic failure point, we will almost always recommend the metal option.
It may cost a little more for the part.
But if you're paying several hours of labour to get to it, spending a little more for a more durable component makes sense.
We'd rather fix the weak point than reinstall it.
Building a Vehicle and Keeping One Are Two Different Things
Modern vehicles are lighter, safer, cleaner and more efficient than ever.
Those are real accomplishments.
But efficiency doesn't automatically mean durability.
Sometimes making a vehicle lighter means compromises have to be made somewhere else.
And based on what we've seen repairing vehicles over the years, we believe consumers are increasingly being asked to absorb the long-term repair costs of some of those compromises.
What's especially interesting now is that the manufacturers themselves are beginning to offer metal replacements for some components that originally came in plastic.
To us, that says a lot.
The engineers already know how to make the part more durable.
The question is why the more durable version wasn't installed from the beginning.
At POCO NAPA AUTOPRO, when we have the choice between replacing a known plastic failure point with another plastic component or installing a proven quality metal upgrade, we'll recommend the metal upgrade.
Because our priority isn't getting the vehicle through its first few years.
It's helping you keep it reliable for the years that come after.