Agree with Bimmer_boy (yeah I know some Gaelic) ............torque is really the reason to go with diesel or not. With increased cost of the X and increased cost of diesel you would need to be doing crazy miles to break even.
If towing is very important to you than the torque of a diesel is a no-brainer.

That torque will help you climb the hills while towing, but the lack of engine braking with the diesel will make descending less of a pleasure. If BMW want to make the diesel X5 a real tow vehicle, they will have to think about an engine exhaust brake.

The increased brake rotor size (if true) is likely a nod to the reduced engine braking, to result in the same effective braking power. That doesn't plan for a trailer, which will need increased trailer braking compared to a gasoline model.

I imagine that they may not offer an engine brake for NVH reasons.

Btw, don't diesel engines (at least on-highway) have throttle these days for egr?

They may be using a throttle for EGR, but not necessarily. Haven't seen any design details on that. Would be interested in what the engine braking is like on a current BMW X5 diesel while towing.

Just poking at the thought that the only thing that matters is accelerating up a hill. We all have to go down those hills as well. Jake Brakes and other designs all existed for a reason. They are even recommending exhaust brakes on diesel pickups these days for heavy towing.

Any bets that BMW finds problems with the Urea injection system, particularly in cold climates, after they start selling them in the U.S.?

I do like BMWs, but BMW's record with their inital usage of new technology isn't the best in the automotive World.

Not disagreeing that an engine brake is very important in a lot of towing diesel applications. I believe the Cummins light-duty engines even have a Jake Brake option from the dealer.

Thinking back, I'm pretty sure almost all the newer diesel engines (since whenever egr started becoming used in diesel for emissions) come with some form of throttle at the mainfold entry. Not sure exactly why a throttle is needed. I think there needs to be a vacuum situation in the manifold to get the egr system to flow, and that's not going to happen with a turbocharged engine. Even looking at the current BMW diesel, there's a throttle right before the manifold. #3 is the throttle, #1 the egr valve.

If a gasoline engine X5 can tow 6,000lbs and be ok with just the axle brake and the throttle, the diesel version should be fine too with the same setup. Compression and Exhaust brakes are mainly used when the towing capacity is so great that large enough axle brakes can't be feasably fitted, enough to slow down the load. I don't think such a situation would occur with the X5 unless the diesel model can tow substantially more. The larger brakes on the SD diesel model might be because of a greater towing capacity, but I thought it was primarily for Efficient Dynamics?

Sorry if I'm a newb to this, but what's the matter with diesels and engine braking? I notice that the automatic transmissions on busses just lock the torque converter and utilise the engine braking. :dunno: So how is this any different from normal vehicles?

Diesel engines don't normally have throttles (just an open inlet), so there's no way for the piston to create mechanical loss.

Vin covered it, but essentially since there is no throttle on a diesel engine (air just flows straight in), when you lift your foot off the accelerator you will not notice any particular retardation. It can be disconcerting to drivers accustomed to gasoline engines, since gearing down doesn't do much. Not very important on a passenger car, but if we start to think of the diesel X5 as "the ultimate towing BMW" as was proposed earlier in this thread, then engine braking could become an issue.

Heavy duty diesels have one of two forms of additional braking: A compression brake (ie a Jake Brake) uses another lobe on the camshaft to lift a valve when activated, releasing the compressed air at the top of the power stroke, and venting it to atmosphere. You will notice this on a dump truck near the city, when you hear a loud machine-gun like noise on deceleration (these brakes are usually banned within city limits). Another form of engine brake is an exhaust brake, which essentially closes the exhaust system after the turbocharger, letting the restriction back up to the engine and resulting in a retarding force. That type of system is more popular on diesels for pickups, etc, and may be used on a bus.

I haven't driven a diesel X5, so I would be interested in comments from those who have towed 5000+ lbs with a diesel BMW, how the engine braking is in practice.

weird, this is the complete opposite to my experience in every diesel I've driven, which exhibit far greater engine breaking than gasoline engines I've driven. I'd always assumed it was due to the compression ratio


in my nissan patrol for example, I can drive 60k's from my house to the office in normal traffic and only use the brakes 5 times in total where an intersection or traffic lights require it - this is because when I stop accelerating there's a LOT of engine braking. I can't even come close to the same type of low brake useage in my wife's jeep wrangler. both vehicles are manual transmissions.


even in my X5 which is a 3.0sd which obviously has an auto transmission, there's quite a bit of engine braking going on because the transmission is often smart enough to change down for me on descents and even flats under certain conditions. I noticed the difference quite starkly between both the 3.0d/3.0sd and the gasoline 4.8 when I took them for test drives.


another example with the nissan again - I have 85% reduction gears in it (low range only) and my friend with the gasoline engine has the same gears, along with the same transmission and diffs. on really steep declines, the type where you need the seatbelt to stop you sliding into the dashboard, his vehicle will gather more speed than mine despite mine weighing far more.