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2010 2011 BMW 5 Series Forum F10 BIMMERPOST Universal Forums General Automotive (non-BMW) Talk + Photos/Videos Are composite or plastic engine parts that bad?
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      02-06-2024, 06:46 PM   #1
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Are composite or plastic engine parts that bad?

Nearly every automaker (not just BMW!) is using composite materials (fiberglass reinforced thermoset plastic) instead of cast aluminum for certain parts, especially valve covers and cooling system parts.

VW/Audi cars are known for those composite oil pans that crack easily, BMWs are known for composite cooling system parts that leak, even Toyota, a brand known for reliable cars, is using composite valve covers and cooling system parts.

In infrastructure, plastic and composite materials are used for everything from water and gas mains to high voltage utility pole insulators (instead of ceramic). Modern materials can be strong, lightweight, flexible, and corrosion resistant.

So, are plastic auto parts a bad thing? Or is it just another "they don't build them like they used to" thing from boomers?
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      02-06-2024, 08:58 PM   #2
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Your question is about 35 years past due.
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      02-06-2024, 10:33 PM   #3
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Quote:
Originally Posted by spicyB48 View Post
So, are plastic auto parts a bad thing? Or is it just another "they don't build them like they used to" thing from boomers?
Both. They are mostly fine except when they aren't, and that's the only problem.
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      02-07-2024, 05:49 AM   #4
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      02-07-2024, 08:01 AM   #5
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For the consumer; yes, they're junk, and don't hold up over heat/time.

For the manufacturer; no, they're junk, and don't hold up over heat/time.

Always remember that cars are engineered to be a multi-year source of income for a brand through parts, and labor. The vehicle needs to survive, but it has to nickel and dime you as it gets older. In the case of brands like BMW, Merc, Aston, etc, they need to cause the 3rd owner to become a mechanic to be able to afford to keep it on the road.
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      02-07-2024, 11:26 AM   #6
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Quote:
Originally Posted by ///MPhatic View Post
For the consumer; yes, they're junk, and don't hold up over heat/time.

For the manufacturer; no, they're junk, and don't hold up over heat/time.

Always remember that cars are engineered to be a multi-year source of income for a brand through parts, and labor. The vehicle needs to survive, but it has to nickel and dime you as it gets older. In the case of brands like BMW, Merc, Aston, etc, they need to cause the 3rd owner to become a mechanic to be able to afford to keep it on the road.
Well, considering that Toyota is also switching to plastic parts (a few years ago they started using plastic valve covers) and they are known to be very reliable, plastic can't be too bad.
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      02-07-2024, 12:38 PM   #7
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I needed a new palstic gas tank and valve cover for my 2018 M3. I've never had to replace either of those parts in any of my previous 70 cars. Luckily I have a 3rd party extended warranty as it has covered almost $7k in these repairs the past five months.

This plastic shit is crap.
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      02-07-2024, 01:02 PM   #8
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      02-07-2024, 01:25 PM   #9
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Quote:
Originally Posted by spicyB48 View Post
Well, considering that Toyota is also switching to plastic parts (a few years ago they started using plastic valve covers) and they are known to be very reliable, plastic can't be too bad.
Is it now that I should remind you that Toyota isn't infallible? That they have many engine oil issues causing the need for rebuilds at 90-150K? Do a little research, they make mistakes.
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      02-07-2024, 01:31 PM   #10
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I don't think in most cases they are bad but some manufactures struggle with sealing the plastic parts to metal surfaces. Honda hasn't been able to design a plastic valve cover that doesn't leak oil on their turbo 4 cylinder engines. VAG hasn't been able to make a plastic water pump or thermostat housing that doesn't leak coolant for a good decade. I think they work better on parts like intakes as with 3D printing they can now make intakes that are lighter and flow much better than cast aluminum. In general most engine bays today are filled with plastic and cars today are as reliable as they have ever been so I don't think it's much to get concerned about.
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      02-07-2024, 02:35 PM   #11
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In most cases, no, it's not a problem. Plastic these days is pretty robust. Though, there are some parts that shouldn't be plastic, especially those in high heat, high stress areas, and/or not easily accessible areas. Engineers should know better.

The old mechanics that bitch about this stuff and talk about the glory days of when everything was "metal" seem to forget that cars back in the 50s, 60s, and 70s were generally looked upon as disposable. People bought new cars every 1 to 5 years and most cars rusted out within 7-8 years if they lived in an area with salt treated roads. In general, people own their cars far longer longer and cars in stay on the road longer as well. Cars are also far more reliable than they've ever been, all things considered.

I have little sympathy when people bitch that their 10+ year old car has developed a rash of issues. Stuff wears out over time, regardless of mileage. The reality is people have gotten used to how reliable their cars are and tend to loose their mind when they actually have to make some repairs. Cooling systems, regardless if they are metal, plastic, rubber, etc. are under a ton of stress. It's not odd that a lot of cooling system parts may need to be replaced at 10-15 years. No manufacturer is immune to this. It was like this in the 1950-1990s too.
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      02-07-2024, 02:52 PM   #12
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Quote:
Originally Posted by XutvJet View Post
In most cases, no, it's not a problem. Plastic these days is pretty robust. Though, there are some parts that shouldn't be plastic, especially those in high heat, high stress areas, and/or not easily accessible areas. Engineers should know better.

The old mechanics that bitch about this stuff and talk about the glory days of when everything was "metal" seem to forget that cars back in the 50s, 60s, and 70s were generally looked upon as disposable. People bought new cars every 1 to 5 years and most cars rusted out within 7-8 years if they lived in an area with salt treated roads. In general, people own their cars far longer longer and cars in stay on the road longer as well. Cars are also far more reliable than they've ever been, all things considered.

I have little sympathy when people bitch that their 10+ year old car has developed a rash of issues. Stuff wears out over time, regardless of mileage. The reality is people have gotten used to how reliable their cars are and tend to loose their mind when they actually have to make some repairs. Cooling systems, regardless if they are metal, plastic, rubber, etc. are under a ton of stress. It's not odd that a lot of cooling system parts may need to be replaced at 10-15 years. No manufacturer is immune to this. It was like this in the 1950-1990s too.
I agree. Cars are harder and more expensive to repair nowadays, but repairs are needed far less often. A 10-15 year old car will likely need some parts to be replaced, but your engine probably won't need a full teardown and rebuild until 300k or more. Unless you have a Volvo, then the engine will fail before 100k.
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      02-07-2024, 02:53 PM   #13
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Quote:
Originally Posted by heavyD^2 View Post
I don't think in most cases they are bad but some manufactures struggle with sealing the plastic parts to metal surfaces. Honda hasn't been able to design a plastic valve cover that doesn't leak oil on their turbo 4 cylinder engines. VAG hasn't been able to make a plastic water pump or thermostat housing that doesn't leak coolant for a good decade. I think they work better on parts like intakes as with 3D printing they can now make intakes that are lighter and flow much better than cast aluminum. In general most engine bays today are filled with plastic and cars today are as reliable as they have ever been so I don't think it's much to get concerned about.
Doesn't VAG use plastic oil pans that are notorious for cracking when hit by debris?
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      02-07-2024, 02:54 PM   #14
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Quote:
Originally Posted by ///MPhatic View Post
Is it now that I should remind you that Toyota isn't infallible? That they have many engine oil issues causing the need for rebuilds at 90-150K? Do a little research, they make mistakes.
Nope, I know that Toyotas have plenty of problems too. I think their reputation for reliability came from a few models that have that "refuse to die" reputation, but they will need maintenance and repairs just like any other car.
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      02-07-2024, 03:18 PM   #15
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Quote:
Originally Posted by XutvJet View Post
I have little sympathy when people bitch that their 10+ year old car has developed a rash of issues.
I'm the opposite, I lose my mind when manufacturers SELL you the dream of extended life and reliability only to have their product need a transmission or engine at 100K miles when in the 70's they could make an engine that lasted a million miles.

If they're going to sell me their products that way, I'm going to hold them to it. Now, if they didn't sell it that way, if they didn't play the reliability/longevity card it'd be different, but they do, and are therefore responsible for negative outcomes if I've done all my service.
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      02-07-2024, 03:23 PM   #16
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The problem isn’t the plastic, it’s designing that same plastic part in the same way we built aluminum products.

Plastic is soft, ages and distorts over time and generally needs far more ribs/gussets and additional material for it to compete with metal.

Trying to save weight where you shouldn’t is the engineering issue, I should never have to replace a $500 valve cover because it cracked or warped from age.

End of story.
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      02-07-2024, 03:28 PM   #17
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Don't get me started. Nowadays cars manufactures are switching to soy based insulation wire to wiring their cars. Easy to say from the car manufactures to keep our planet green. Very expensive repair for car owners to fix the damage from rodents chewing through the insulation of the wiring.
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      02-07-2024, 03:38 PM   #18
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Quote:
Originally Posted by eugenebmw View Post
Don't get me started. Nowadays cars manufactures are switching to soy based insulation wire to wiring their cars. Easy to say from the car manufactures to keep our planet green. Very expensive repair for car owners to fix the damage from rodents chewing through the insulation of the wiring.
That sounds a lot like start stop systems - reduced battery and starter lifespan, no real benefit to the consumer. Except it is far more expensive to fix.

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      02-07-2024, 03:55 PM   #19
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Quote:
Originally Posted by spicyB48 View Post
That sounds a lot like start stop systems - reduced battery and starter lifespan, no real benefit to the consumer. Except it is far more expensive to fix.

Grüne? Nein danke!
Exactly. End up we are producing more wastes to our planet and we have less money in our pockets.
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      02-07-2024, 05:54 PM   #20
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Quote:
Originally Posted by spicyB48 View Post
Doesn't VAG use plastic oil pans that are notorious for cracking when hit by debris?
All the Germans use plastic oil pans.
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      02-07-2024, 07:46 PM   #21
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The plastic crap on my E90 335xi was a joke. Plastic is bad & doesn't belong in a lot of places.
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      02-07-2024, 10:36 PM   #22
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Quote:
Originally Posted by ///MPhatic View Post
I'm the opposite, I lose my mind when manufacturers SELL you the dream of extended life and reliability only to have their product need a transmission or engine at 100K miles when in the 70's they could make an engine that lasted a million miles.

If they're going to sell me their products that way, I'm going to hold them to it. Now, if they didn't sell it that way, if they didn't play the reliability/longevity card it'd be different, but they do, and are therefore responsible for negative outcomes if I've done all my service.
Motors back in the 70s rarely made it to 150k miles, especially domestics.
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