How to drive the mighty 335d Super-diesel to excellent FE. [xfloat=left]http://www.cleanmpg.com/photos/data/501/Passenger_Side_Rear_in_the_rain.jpg[/xfloat]Wayne Gerdes - CleanMPG - April 20, 2009 2009 BMW 335d – 27 mpgUS combined and worth almost 50 with a little work from you. Techniques Explained Basic accelerations - With no one following, acceleration from 0 mph can be accomplished with a light touch of the throttle and use of the paddle shifters to up shift from gears 1 and 2 when 1,450 RPM is seen on the tachometer. From gears 3 and 4 up shift via the paddle shifters at just 1,400 RPM and a light touch will maintain above 30 mpg during the acceleration. Once in fifth, shift via the paddle shifters at 43 mph and the BMW will maintain sixth gear with the iFCD holding above 50 mpg. Gentle acceleration up into the 48 mph + range during slower speed city/suburban cruise maintains this level of FE, but be ready for NICE-Ons for any slow downs. Fuel cut should only be used if a stop is required of course, and the paddle shifters can be utilized during deceleration to stay above 1,000 RPM. At speed FASing in the 335d is not only unwise per the manual (which specifies no flat towing), but impossible due to a shut down lockout at any speed other than stopped via the Push Button. As diesels utilize extreme lean-burn A/F ratios at low loads, the best practice is to get the heavy 335d rolling and maintain momentum with strict attention paid to DWL. City [xfloat=left]http://www.cleanmpg.com/photos/data/523/37_9_mpg_at_20_4_mph_-_NY_City_Rush_Hour_Commute_SMALL.jpg[/xfloat]NY City during Rush Hour FE test results - 37.9 mpgUS at 20.4 mph over 23 miles. A light touch of the throttle on any acceleration while using the paddle shifters as described above and moving to NICE-On’s for any slow down is optimal for this vehicle. If a lengthy stop is anticipated, go ahead and FAS at the light but remember that diesels burn only about a quarter the amount used by SI-ICE (gasoline engine) vehicles at idle. Additionally, it takes quite a bit of cranking power to turn the 335d’s 16.5:1 compression ratio over. Because of these factors, shutdown should only be utilized for stops longer than 20 seconds. Since you cannot FAS the 335d at anything other than a full stop, this technique was used only 3 times during the hour and 16-minute nightmare commute. There is a Neutral lockout below 3 mph until stopped so if you find yourself in this situation, open up an even larger than normal inner city buffer, accelerate to 3 + mph and than NICE-On Glide back down to 0 mph to remove the big 6-speed AT and related power losses from its TC when dealing with stop and go traffic. And it is imperative that your mindset sticks to 3-Lights out anticipatory focus. You simply have to catch more green lights in the inner city or your segment is going to be wiped out. 2009 BMW 335d - NY City during Rush Hour FE Testing ----Leaving a 7-mile FE test loop deep into NY City’s inner sanctum.-------NY City’s I-495 during the city’s afternoon Rush Hour stop and crawl. Both part of the 23-mile inner City/Interstate rush hour FE testing. Highway [xfloat=left]http://www.cleanmpg.com/photos/data/523/53_4_mpg_at_64_8_mph_SMALL.jpg[/xfloat]All highway drive on the way back from NY City. 53.4 mpg at 64.8 mph over 120 miles. Unfortunately this included a strong tailwind aid While on the way back from NY, we were experiencing strong tailwinds allowing far above normal FE results for the speeds we were traveling so I did not report the results of the entire drive back given they were very unrepresentative. We were traveling with average speeds between 65 and 70 mph including the stops to swap on both ends and still achieving FE results between 48.0 and 54.7 mpg! While on the highway in a climb, DWL to a comfortable minimum speed and hold. Once the crest is reached, a NICE-On can be used if there is a long and relatively steep descent on the backside little or no acceleration to reach an acceptable top speed for the rest of the hill or mountain. For steady state cruise, choose your desired FE per the analog iFCD and drive. Unfortunately, the steady state while DWL FE testing results occurred in 38 to 39 degree F temperatures with a 15 + mph strong side wind so the results shown will not be representative of actual unfortunately Reasonably steady state FE capability Column1Column2Column3mphmpgUSNotes 40465th Gear and ~ 1,250 RPM 54506th Gear and ~ 1,250 RPM 60416th Gear and ~ 1,500 RPM 70386th Gear and ~ 1,775 RPM There is a warm-up hit but it is not nearly as intrusive as that of a Hybrid or most conventionally powered automobiles. Just work though it and move on gently. A DPF regeneration event is much more damaging to FE. While on the way home after an overnight rest stop, only 30 to 35 mpgUS on the iFCD was achievable for close to 20 miles. The DPF regeneration event is based on DP across the filter and if it happens at lightly loaded highway cruise, it can last for upwards of 20 miles. That 100 mile segment ended up at just 43 mpgUS because of this behavior. We were fortunate not to have encountered one of these events on the drive up to NY as it likely would have prevented completion of the trip on a single tank. Max fuel tank capacity and fuel starve The BMW 335d is equipped with a 16.1 gallon tank and holds at least 16.485 gallons to near fuel starve as we discovered. With the manual stating a 2.1 gallon reserve and seeing the Low fuel light at exactly 100 miles DTE while still holding 49.0 mpgUS from the FCD, it is wise to heed the warnings. When near 0 DTE, you will see positive numbers and – (less than 0 miles DTE) depending on terrain. In either case, fill up before you get to that point!
Great work, Wayne and Ken! I'm also a little jealous that you got to drive such a fine automobile Is there an indicator that the DPF regen is taking place, or was your only clue the reduced fuel economy?
Hi Mike: ___Nothing but the iFCD hanging in the low to mid 30's no matter what speed or load I was driving. This also occurred in the flats of Ohio and we had a tail wind too so it was definitely a DPF regeneration. ___We spoke with the Tech lead for BMW at the NY Auto Show Press Event about a DPF regeneration and he said when the DP rises to the setpoint, the Regeneration will go on "for quite some time." And it did too! ___And we were truly fortunate that it happened on our way home instead of on our way out as we needed every drop ___By the way, what did you think of the 335d’s overall review? ___Good Luck ___Wayne
I thought both the review and this FE technique description are very good, it's probably the most useful information I've seen on the car to date. The conclusion in the review is almost spot on with my feelings on the car. I have one question about the review though, why does the incorrect fueling protection system need improvement? Do some diesel nozzles not work in the car? If so, I would be tempted to try to remove that system if it ever came installed on my car. The new cars can't use truck pumps and that is bad enough, but to make the car incompatible with some regular diesel pumps would be a definite annoyance to me. One last useless detail, I flinched a little when I saw the fuel filler cap hanging against the side of the car. If it's dusty, I often end up with a little dark spot on the side of my car from dust sticking to the oily residue left behind if I let my filler cap dangle. I was much happier to see the next picture with the filler cap in its proper storage location. Just some silly little diesel quirk that the other 99% of people would never worry about
The note about regen got me thinking. Different manufacturers probably have a variety of ways to trigger and modulate the regen cycle, but I'm under the impression that DPF's plug faster when the engine isn't working very hard and isn't putting as much heat into the exhaust. So what would happen if you picked a long uphill stretch and ran up it with the intention of making some heat? You could run the engine closer to optimum BSFC (near peak torque, maybe 3/4 load) I'm sure this would use more fuel than the usual hypermiling tricks, but might pay off in less fuel used in regen, and the hill gives you a chance to "store" some of that extra power in both kinetic (keeping your speed up) and potential (going up hill) energy. What do you think? Do modern (2007 and newer) diesels present an opportunity to come up with some new hypermiling tricks to minimize the impact of regen?
Perhaps. Though managing PM is tricky. The light throttle urban stop/go driving probably contributed most to DPF plugging. Fuel/air mix is not as complete and combustion temps drop resulting in increased PM. But there is a balance to be struck: improving fuel/air mix increases NOx emissions, especially in low rpm/ high torque demand situations. Running the vehicle hard up hills may help, but I'm guessing the temp won't remain high long enough to undo the impact of low speed driving. I've read about Volvo diesels in the UK that have to go in to the dealer for manual regen, as the cars' run solely in urban environs, and the computer generated regens aren't enough to clear the DPF. Wayne- curious about the higher rpm for 1st to 2nd than for the rest of theshifts. Is the first step that much higher? This is different than big diesel progressive shifting recommendations. Keith
Wayne, I recall hearing that newer BMWs with automatic transmissions can only be started if they're in PARK, with the brake depressed - no start-ups from neutral. Did you notice this at all while you were doing city driving? Is that what you meant by neutral lock-out?
Wayne, For what it's worth, I found the write up very informative. Thank you for conducting the test drive and providing the subsequent write up!
Thanks for the great writeup! I too am curious about the shift from 1 to 2 recommendation. Many BMW people are saying that even for speed 0-60, starting in 2nd gear is the best way to go. Would it possibly also be the most efficient for MPG to start in M2?
One of the main questions I have is whether I should be pulsing and then gliding in neutral or should I leave it in 6th gear and let the fuel auto cut off? Which is more efficient for my 335d diesel engine? What about a 1 mile long dowhill? Neutral or in-gear? My car will not allow FAS. Thanks!
As a general rule , you need to determine/guess WHEN you will need to slow/stop in the next 30-45 seconds. If you can , try to glide in neutral. If you think you will need engine braking , stay in gear. Keep alert and look for opportunities to glide.
