Alarming use of plastic for engine parts = probable premature failure

There is a rather alarming (IMO) trend in the automotive industry toward using plastic for certain engine parts. To be fair, it's not just BMW following this trend, but many others as well. Plastic instead of metal is being used for things like oil pans, intake manifolds and valve covers to name a few. However, in general, plastic and heat don't mix. I don't care what flavor of plastic is used, it's going to fail far earlier that a metal counterpart. The OEM's motivation is more than likely cost, as the tooling and materials for a plastic part are much cheaper than a metal one. But, are they passing those savings onto the consumer? Doesn't look like it; looks more like they are cutting their own costs while increasing the cost of ownership through more frequent repair needs.
My '05 545i had very few problems during the 4 year maintenance contract period, but shortly thereafter things went sour. With only about 70k miles on it, the plastic bit of the radiator failed, resulting in a leak, and necessitating the replacement of the whole thing. The Mechatronics sleeve (in the transmission) sprung a leak (this I understand is common on the 5), the active sway bar pump sprung a leak, the alternator went on the fritz, the plastic transmission pan itself warped and sprang a leak at the drain plug, and finally the engine oil pan has a leak as well. $6000 to repair all of the critical bits; both the oil pan and active sway motor still leak. Wow, what's next? I have worked in electronics high-tech industry for over 20 years and many of my colleagues have owned BMWs of one sort or another. It's very common to hear how happy so-in-so was about getting rid of their Beemer after the maintenance contract expired.

Very common in all vehicles.I work in the auto industry for Toyota and this is being done for weight reduction also.We currently use a steel fuel tank but many have gone to plastic fuel tanks.Cafe standards are pushing manufactures for better and better fuel mileage while the consumer wants better safety features power etc etc.

Actually plastic does a better job at dissipating heat a bit better that metal for certain functions. It's cheaper to use, safer and lighter as you say.
That's generally the reason more lives are spares during high speed crashes. If you look at cars built prior to the turn of the century you'll see they are heavy and just a tap to the knee can kill you. I don't think we are using the best components for cars right now in terms of perfection, but as time passes by we will definitely get there. It does however meet the criteria for today's standards in terms of pedestrian safety, efficiency etc...

Originally Posted by boramkiv

Actually plastic does a better job at dissipating heat a bit better that metal for certain functions. It's cheaper to use, safer and lighter as you say.
That's generally the reason more lives are spares during high speed crashes. If you look at cars built prior to the turn of the century you'll see they are heavy and just a tap to the knee can kill you. I don't think we are using the best components for cars right now in terms of perfection, but as time passes by we will definitely get there. It does however meet the criteria for today's standards in terms of pedestrian safety, efficiency etc...

While I might agree that today's cars are safer than they were years ago, you can't be serious in saying they are lighter in weight. I just read a study that showed that, due to the sale of so many gargantuan sized SUV's, crossovers, and minivans, the weight of the average vehicle on the road today is actually heavier than it was in 1970!

I was thinking along the lines of like a Cadillac Eldorado and such. Also there were virtually no SUV's back then. Thing is everyone wants a safe car and many think bigger (SUV or similar) is safest. You're right cars on the road are heavier than they were back then, but they are filled with more electronics and gadgets. An SUV today weighs what a big car did back then. There are also many, many more cars on the road today than ever before.

1970's cars are death traps on wheels . . .

Yes true cars are still very heavy but manufactures are still fighting weight savings more than ever.1970s cars didn't have 8 or more air bags,Multiple computer modules,Dual zone climate that requires 2,3,4 evaps,catalytic converters with more room for the same size car.Also some of these plastic cars last for many uneventful miles.My 70s car were ready for the scrap heap at 100,000 miles.I mean ragged out.

Originally Posted by boramkiv

Actually plastic does a better job at dissipating heat a bit better that metal for certain functions.

Sorry, but plastic is not a better heat conductor vs. Metal. What business do you work in, engineering? Perhaps you might convince me of plastics embedded with bits of metal throughout could draw heat away from the source. If your theory is correct, then why didn't they just go all out with a full polymer coolant, oil, and tranny radiator. The reason being is that Aluminum fins are more durable, light weight and they dissipate heat much more efficiently that wood, plastic, glass, or rubber. Our magnesium/Aluminum engines are very efficient at sucking away a high level of heat from the core of the enginges friction areas, ie. pistons, crank, valves, camshaft, bearings, etc. The cooling radiators help carry that excess heat even further away from the mechanical systems. Polystyrene doesn't make a good engine block my fellow Bimmer enthusiast.

Originally Posted by boramkiv

Actually plastic does a better job at dissipating heat a bit better that metal for certain functions. ...snip

Can you explain that statement. I like to learn new things.

Originally Posted by UltimateDriving

1970's cars are death traps on wheels . . .

Not surprising since they are 40 years old.

Well lets see, there's a plastic air box, plastic intake tubing all the way to the intake manifold which is also hard plastic. There's plastic battery box covers on (not our fives) but modern cars that still have the battery under the hood. Valley pan covers. There is hard plastics for coolant connecting joints and elbows. The majority of the heat a car generates is under the hood, and that's where most of the plastics reside.

http://www.dailytech.com/Plastics+En...ticle16684.htm

The car is also able to cool down somewhat faster because of these pieces. Yes metal is definitely a better option for heat transfer and conductivity, but you don't necessarily want the slightest amount of heat to cause your intake manifold to reach high temps quickly. So I used the word dissipate wrong up above. It doesn't heat up as much to be able to transfer that heat which is why I used dissipation. Plastics will be used wherever possible as to reduce weight and minimize heat buildup. Carbon fiber is on the way in now.

http://www.assemblymag.com/articles/...under-the-hood

Originally Posted by DanaWDavis

There is a rather alarming (IMO) trend in the automotive industry toward using plastic for certain engine parts. To be fair, it's not just BMW following this trend, but many others as well. Plastic instead of metal is being used for things like oil pans, intake manifolds and valve covers to name a few. However, in general, plastic and heat don't mix. I don't care what flavor of plastic is used, it's going to fail far earlier that a metal counterpart. The OEM's motivation is more than likely cost, as the tooling and materials for a plastic part are much cheaper than a metal one. But, are they passing those savings onto the consumer? Doesn't look like it; looks more like they are cutting their own costs while increasing the cost of ownership through more frequent repair needs.
My '05 545i had very few problems during the 4 year maintenance contract period, but shortly thereafter things went sour. With only about 70k miles on it, the plastic bit of the radiator failed, resulting in a leak, and necessitating the replacement of the whole thing. The Mechatronics sleeve (in the transmission) sprung a leak (this I understand is common on the 5), the active sway bar pump sprung a leak, the alternator went on the fritz, the plastic transmission pan itself warped and sprang a leak at the drain plug, and finally the engine oil pan has a leak as well. $6000 to repair all of the critical bits; both the oil pan and active sway motor still leak. Wow, what's next? I have worked in electronics high-tech industry for over 20 years and many of my colleagues have owned BMWs of one sort or another. It's very common to hear how happy so-in-so was about getting rid of their Beemer after the maintenance contract expired.

Yes it's really bad I was surprised to find in early model Audi S4 (V8) has plastic valve cover that in the time chipped by layers. Remember it's v8 in the very small engine bay where there is no airflow what so ever.

About dissipations; Yes the aluminum dissipated faster then plastic, but it's produce some composite material that do as good as ceramic.
Ex: thermal conductivity for aluminum : around 180 W/mK
thermal conductivity for copper : around 360 W/mK
thermal conductivity for steel : around 16 W/mK
thermal conductivity for composite : around 5-30 W/mK
thermal conductivity for plastic : around ~ .5 W/mK max