Forget MPG ... Best Long Term Option 50i or 35d

[JCL]

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.

[diesaroo]

Originally Posted by JCL

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.

[radelow]

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.

[o-steve]

I hate to say it but I wouldn't even know where to purchase Diesel fuel. Its just not stocked at many local gas stations. The inconvenience of that in itself would be enough to run the other way...

[Penguin]

Originally Posted by o-steve

I hate to say it but I wouldn't even know where to purchase Diesel fuel. Its just not stocked at many local gas stations. The inconvenience of that in itself would be enough to run the other way...

The fact that the diesel typically can go 500-600 miles between fill-ups alleviates that concern somewhat. With the popularity of diesel pick-ups for many years, diesel is actually pretty easy to find. I've got 27,000 miles on mine, driving all over the Midwest and West, and only had a problem once, and that was only because I wanted a name-brand diesel fuel rather than using a small, independent generic station.

P.S. While far from 100% accuracy, the BMW Nav system can search for stations with diesel along your programmed route, or near your current location.

[diesaroo]

Originally Posted by radelow

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.

Well that was an entertaining rant but you forgot to neglect fuel mileage as part of the discussion as the OP had requested.

Also, before you start making assumptions about who has what education and job title, you may want to tread lightly as there are many engineers on this forum whose experience you know nothing about.

As a counterpoint, if you want to talk about years of diesel experience, they don't come any older than Mercedes. But really none of them have a lot of experience with common-rail, egr, dpf, and scr. It's such a new technology that nobody really knows how it will age.