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  #41  
Old 11-27-2011, 09:40 AM
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I posted this before in a previous thread on here--this is from late last year.

Class Action Suit On BMW N54 Turbo Engine For Defective High Pressure Fuel Pumps and Turbo Chargers
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  #42  
Old 11-27-2011, 03:24 PM
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Originally Posted by Penguin View Post
I'm surprise no one has mentioned the diesel's SCR exhaust fluid injection system. This is rather new, and was introduced first for the U.S. market, e.g., no long term real life experience at all, unlike the basic diesel engine design where BMW has been selling many diesels in Europe for many years.

I expect that the newly-designed SCR system introduced for the first time with the U.S. diesel has the most risk for long-term problems vs. the V8.
very true. But to play devils advocate, the diesel has cast iron cylinder liners and only simple angles on the timing chains (3). Not sure about the V8 per se, but most bimmer gas engines have nikasil/alusil coated cylinders (not as durable as iron) with the V8 having one long convoluted chain which may be more susceptible to stretch than a simple 2 pulley arrangement.
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  #43  
Old 11-27-2011, 09:33 PM
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Originally Posted by BGM View Post
I posted this before in a previous thread on here--this is from late last year.

Class Action Suit On BMW N54 Turbo Engine For Defective High Pressure Fuel Pumps and Turbo Chargers
Neither 50i nor 35d uses the N54 engine. How is this class action relevant to this discussion?
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  #44  
Old 11-28-2011, 11:36 PM
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Originally Posted by Armand View Post
Neither 50i nor 35d uses the N54 engine. How is this class action relevant to this discussion?
BMW Defective Turbocharger & Fuel Pump Class Action
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  #45  
Old 12-06-2011, 02:47 PM
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I think both engines will last a long time but everything that's bolted to them will more like be the points of failure.

on the diesel you have high pressure fuel pump(s) and turbos...

on the V8 you have less parts to fail.
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  #46  
Old 12-09-2011, 04:20 PM
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I think all things being equal, cylinder bore to piston ring wear on a diesel would always be lower than gas because max torque arrives at a much lower rpm. In other words, over the same amount of miles the engine will have rotated much less on a diesel than a gas.
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  #47  
Old 12-09-2011, 07:22 PM
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But other things aren't equal. I agree that a lower speed engine will have potentially less cylinder bore wear, but recall that the gasoline version is now turbocharged and gets its peak torque at a similar rpm to the diesel. My 535i reached peak torque at 1300 rpm, and I would expect the V8 to be somewhat similar.

Now add in the peak cylinder pressures from the diesel compared to the gasoline version. This will impact block fatigue, bearing loads, and thust loads on the piston and cylinder wall.

I know that piston loads increase with the square of engine speed, and only linearly with increased cylinder pressures, but the diesel always has higher cylinder pressures, and the gasoline engine is only occasionally at higher rpm.

All in all, I would call it a wash. There is no logic to the diesel lasting longer, but it shouldn't last any less time, either. And it isn't like the transmission, ancillaries, and electronics are still going to be working as new when the engine finally does give out.
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  #48  
Old 12-09-2011, 09:20 PM
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  #49  
Old 12-09-2011, 10:10 PM
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Originally Posted by JCL View Post
But other things aren't equal. I agree that a lower speed engine will have potentially less cylinder bore wear, but recall that the gasoline version is now turbocharged and gets its peak torque at a similar rpm to the diesel. My 535i reached peak torque at 1300 rpm, and I would expect the V8 to be somewhat similar.

Now add in the peak cylinder pressures from the diesel compared to the gasoline version. This will impact block fatigue, bearing loads, and thust loads on the piston and cylinder wall.

I know that piston loads increase with the square of engine speed, and only linearly with increased cylinder pressures, but the diesel always has higher cylinder pressures, and the gasoline engine is only occasionally at higher rpm.

All in all, I would call it a wash. There is no logic to the diesel lasting longer, but it shouldn't last any less time, either. And it isn't like the transmission, ancillaries, and electronics are still going to be working as new when the engine finally does give out.
One would expect that both the gas and diesel blocks, bearings, etc, would be designed accordingly with those cylinder pressures in mind. But even if the new tubocharged gas engine reaches its torque peak at a similar rpm to the diesel, the fact remains that the siliconized cylinder liners (gas) have historically had lower durability than cast iron (diesel).

Another mark against the gas is the trouble BMW has had with ethanol blended fuel when used in direct injected gas engines (335i). At least in the US, that 10% blend will likely become 25% incrementally in the next 10 to 15 years. A blown HPFP with other collateral damage at higher mileages may send it the junkyard.

The biodiesel OTOH has better fuel properties (cetane, lubricity) than regular D2 so that looks like a plus for future diesel use.

This argument really is academic though in that most BMW owners will not keep their car past 4-5 years, much less 10-15. And those that do will likely have their pocketbook lightened by something else than an engine failure.
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  #50  
Old 12-12-2011, 05:42 PM
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Unless any of you are engineer's that work in the field of internal combustion engines everything you say is based on your best guess and has no basis in the real world.

As I am NOT an engineer I am not going to opine on cylinder pressures, engine speed, or any of the other factors that impact the longevity of an internal combustion engine. All I will say is this, I had the 4.4i V8 X5 before I have the diesel now and I much prefer the diesel for day to day driving. The torque arrives sooner, the power is more than enough and the fuel mileage is heads and tails better. BMW has been building diesel engines for almost thirty years...and have been using turbocharging since the beginning. It is a tried and tested technology and overall diesel engines have been shown to last longer than equivalent gas engines.
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