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BMW Diesel Owners / Enthusiasts
Do you own a diesel powered BMW? Maybe a 335d or a BMW x35d? Come and talk about what makes your car great!

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  #1  
Old 11-03-2014, 02:09 PM
sirbikes sirbikes is offline
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Crazy fuel saving tips for diesels...

I was on fuelly.com today poking around and I checked out the fuel saving tips page. It is one big unorganized list, from sensible to contradictory to downright ridiculous. These two related to diesels caught my eye in particular. The first one probably falls in the ridiculous category. Anyone heard of either of these?

Quote:
Partially Block Off Your Radiator Grill.

This especially applies to diesel vehicles. The sooner your engine gets up to temperature the more efficient it will be. For example my (diesel) car gets almost half the MPGs it would get when up to temperature. I have blocked off the lower grill (with black duct tape) which allows my car to warm up faster and keep a sturdy temperature. This also improves aerodynamics of your vehicle (if done correctly). I am doing this in about 6-15 Celsius weather and see a decent increase in MPG and I can also use my heaters earlier. IMPORTANT Be sure not to block off your intercooler (if fitted) as this helps MPG and keeps intake air temps low and intake air density higher. It is extremely unlikely your vehicle will overheat but for the first few journeys keep an eye on your coolant temp.

posted by Swiftkick on October 26, 2014

this tip works for 43% of voting Fuelly members.



Keep that diesel fuel tank full

Diesel fuel is highly hygroscopic. That means it sucks moisture and water out of the air, on a daily adiabatic cycle. The more air stored in the fuel tank, the more moisture is drawn into the fuel tank, condensing on the inside walls of the fuel tank, as the tank breathes in and out with the daily heat cycle. Keeping your diesel fuel tank fuel limits the amount of moist air drawn into your fuel tank, and into your fuel during humid seasons. This is less a problem in the arid SouthWest seasons with relative humidity below 20%

posted by Magalicious on October 16, 2014

this tip works for 40% of voting Fuelly members
http://www.fuelly.com/tips?page=1
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  #2  
Old 11-03-2014, 02:12 PM
Michael47 Michael47 is offline
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As regards the first one, I'd say the guy is right. He is also very much in need of a new (functioning) thermostat. If your thermostat is stuck open, which is the usual failure mode for them to prevent overheating damage, then blocking off part of the radiator is good advice. If your thermostat is working properly, not so much.
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  #3  
Old 11-03-2014, 04:14 PM
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floydarogers floydarogers is offline
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Quote:
Originally Posted by sirbikes View Post
I was on fuelly.com today poking around and I checked out the fuel saving tips page. It is one big unorganized list, from sensible to contradictory to downright ridiculous. These two related to diesels caught my eye in particular. The first one probably falls in the ridiculous category. Anyone heard of either of these?
TDIWyse has posted a couple things on grill blocking. He lives up in the Great Lakes area (MI, WI?) and it was clear his car never warmed up during the winter on his commute. Getting it operating temp should make it a bit more fuel efficient. Trucks, especially those driving in cold weather do this all the time - it also reduces wind resistance a bit.

I wouldn't worry too much about condensation; no-one has complained about water in their fuel - it gets trapped in our fuel filter, as we don't have a separator.
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Old 11-03-2014, 05:52 PM
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dunderhi dunderhi is offline
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My best tip is to try different fuel stations and keep track of you mileage. There's quite a of variation in CETANE levels. The local Highs Dairy Store chain (Shell or Citgo gas) consistently gave me an additional 2 mpgs. A different Shell station just down the road, but with locally sourced diesel, did not perform as well.
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  #5  
Old 11-04-2014, 06:06 AM
Hoooper Hoooper is offline
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The first one is 100% true on both counts. Blocking off openings to the engine bay will get you better mileage, even regardless of engine temp. The engine temp thing is true from a mileage standpoint, but if your system is working properly it shouldn't make a huge difference. If its REALLY cold out then blocking the radiator is a legitimate need since the thermostat might not be able to properly control at the low amount it can be open and still keep warm. This is not unusual to see in cold climates.
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  #6  
Old 11-04-2014, 11:07 AM
Pierre Louis Pierre Louis is offline
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Quote:
Originally Posted by dunderhi View Post
My best tip is to try different fuel stations and keep track of you mileage. There's quite a of variation in CETANE levels. The local Highs Dairy Store chain (Shell or Citgo gas) consistently gave me an additional 2 mpgs. A different Shell station just down the road, but with locally sourced diesel, did not perform as well.
Impressive mpg with your departed 335d. Most studies don't support the efficiency theory of "better" cetane but it may apply to our engine.

What brands of diesel did the best for you? Around here there is only Shell, Chevron, and BP.

Thanks.

PL
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Old 11-04-2014, 08:23 PM
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dunderhi dunderhi is offline
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Quote:
Originally Posted by Pierre Louis View Post
Impressive mpg with your departed 335d. Most studies don't support the efficiency theory of "better" cetane but it may apply to our engine.

What brands of diesel did the best for you? Around here there is only Shell, Chevron, and BP.

Thanks.

PL
I thought a higher Cetane level resulting in higher mpgs was a given. A quick internet search for Cetane tests seems to support this relationship. For example: http://www.hindawi.com/journals/jc/2012/738940/ I'm curious what tests show otherwise.

Anyway, my experience is that the brand of gas does not correlate to the source of the diesel. There are two Shell Stations near my home. The Shell two miles to the West is owned by a local fuel distributor. They sell Shell, BP, and their own brand of gas at their stations. I got similar mpg performance at several of their stations. Now the other Shell station, which is about two miles to the East of me, is owned by High's Dairy Stores, which is a larger, but primarily a Maryland chain. They sell Shell or Citgo gas at their various stores. The performance that I got from their diesel was consistently better than all of the other stations in my area, so I suspect they only have one source of diesel. Since all of the pumps in my area only state >40 Cetane , one doesn't know if it is 40 or 50. I strongly suspect High's Cetane level is higher than the others, but improved lubricity could also be a part of the mpg improvement.

BTW, I don't work for or own any part of High's.
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  #8  
Old 11-05-2014, 06:30 AM
Pierre Louis Pierre Louis is offline
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Quote:
Originally Posted by dunderhi View Post
I thought a higher Cetane level resulting in higher mpgs was a given. A quick internet search for Cetane tests seems to support this relationship. For example: http://www.hindawi.com/journals/jc/2012/738940/ I'm curious what tests show otherwise.
Thanks for your response.

From the article you mentioned, it is a little disingenuous with its statement about fuel economy as they had several statements implying that fuel composition was related to both CN and fuel economy. That is correlation, not causation. i.e. whatever improved fuel consumption also happened to increase the CN.

The engine used was a bit different from common rail direct injected engines:
Quote:
The tests to evaluate the ignition delay time, specific fuel consumption, and PM and unburned HC's emissions were performed in a Toyama 7.0 Hp single cylinder engine, 250***8201;cm3, operating at 80% of maximum power, with mechanical fuel injection at 13.5 before TDC, average injection pressure of 150 bar, compression ratio of 21***8201;:***8201;1, 3600***8201;rpm, and 10% of O2 in the exhaust gases.
They contradict the later fuel economy results with this statement:
Quote:
The tests performed in this study used the same excess air with all the fuels (same load and very similar specific fuel consumption)
and:
Quote:
In general, it was found that an increase of five units in CN leads to an increase of approximately 40% in PM emissions.
But:
Quote:
In general, it was found that increasing the CN by five numbers leads to a reduction of approximately 20% in HC's emissions.
They did measure "specific" fuel consumption and found under the conditions that were present, fuel with a higher CN did better, but didn't ascribe anything to absolute energy content of each fuel, since the CN varied according to the amount of paraffins etc.:
Quote:
The main indicator is the source of the fuel S1400_51, which, because it is paraffinic, has a higher CN and therefore shows higher emissions of PM and HC's. In general, as the CN increases, the specific consumption shows a clear tendency to decline. In this range of CN (4550), for each additional number in CN, the specific consumption in g kWh***8722;1 decreases in the same proportion.
In the real world, with DDE and different additive packages, the specific fuel consumption in each engine has a varied response to fuel composition as far as fuel economy and is generally thought of as negligible. The 2% or so improvement in fuel economy this study found between CN 45 and CN 50 is entirely consistent with differing energy content of fuel from various sources. The correlation between fuel composition, fuel economy, and CN in this study may be related, but may only be a correlation:
http://www.akenergyauthority.org/PDF...0Additives.pdf
Quote:
Efficiency
Although typically less than 40% of the energy in diesel fuel is converted to electricity in diesel generator sets (or gensets), there is limited room for improvement in diesel engine efficiency that can be achieved by modifying the fuel. This is due to the thermodynamic limit to the efficiency of the diesel cycle, losses due to friction in the engine, and inefficiency of the electric generator. Estimating the amount of energy that is left for the engine to produce electricity based on these limiting factors provides some context for the potential impact of fuel additives.
Even with the outstanding improvements in diesel engine technology afforded by electronic control systems and by adapting fuel injection to changing engine conditions, the overall efficiency of diesel combustion cycles is limited by thermodynamics. This much-studied subject of compression combustion shows that the theoretical maximum ability to convert the chemical energy of a fuel into work in an ideal compression combustion cycle is limited to around 60% [67]. The exact limit depends upon properties of the engine itself (e.g., compression ratio of the engine and when in the cycle the exhaust is expelled in relation to the completion of combustion) rather than the fuel. For non-ideal compression combustion in a relatively small diesel engine, the efficiency is limited to less than 40% primarily due to irreversible processes in the combustion [68].
And: http://www.chevron.com/documents/pdf...TechReview.pdf
Quote:
FUEL ECONOMY
Here again, engine design is more important than fuel properties. However, for a given engine used for a particular duty, fuel economy is related to the heating value of the fuel. In North America fuel economy is customarily expressed as output per unit volume, e.g., miles per gallon. The fuel economy standard in other parts of the world is expressed as volume used per unit distance liters per 100 kilometers. Therefore, the relevant units for heating value are heat per volume (British thermal unit [Btu] per gallon or kilojoules per liter/cubic meter). Heating value per volume is directly proportional to density when other fuel properties are unchanged. Each degree increase in American Petroleum Industry (API) gravity (0.0054 specific gravity decrease) equates to approximately two percent decrease in fuel energy content.
ASTM International specifications limit how much the heating value of a particular fuel can be increased. Increasing density involves changing the fuel's chemistry by increasing aromatics content or changing its distillation profile by raising the initial boiling point, end point, or both. Increasing aromatics is limited by the cetane number requirement4
3 Khair, Magdi: "Combustion in Diesel Engines," ECOpoint Consultants, http://www.DieselNet.com
***65532;***65532;(aromatics have lower cetane numbers [see page 36]), and changing the distillation profile is limited by the 90 percent distillation temperature requirement. The API gravity at 60F (15.6C) for No. 2 diesel fuel is between 30 and 42. The specific gravity, at 60/60F, and the density, at 15.6C, are between 0.88 and 0.82. (See Chapter 4 Diesel Fuel Refining and Chemistry for an explanation of fuel blending, density, and API gravity.)
Combustion catalysts may be the most vigorously promoted diesel fuel aftermarket additive (see page 81). However, the Southwest Research Institute, under the auspices of the U.S. Transportation Research Board, ran back-to-back tests of fuels with and without a variety of combustion catalysts. These tests showed that a catalyst usually made "almost no change in either fuel economy or exhaust soot levels."4
While some combustion catalysts can reduce emissions, it is not surprising that they
do not have a measurable impact on fuel economy. To be effective in improving fuel economy, a catalyst must cause the engine to burn fuel more completely. However, there is not much room for improvement. With unadditized5 fuel, diesel engine combustion efficiency is typically greater than 98 percent. Many ongoing design improvements to reduce emissions may have some potential for improving fuel economy. However, several modern emissions control strategies clearly reduce fuel economy, sometimes up to several percent.
And here: http://en.wikipedia.org/wiki/Cetane_number
Quote:
In short, the higher the Cetane number the more easily the fuel will combust in a compression setting (such as a diesel engine). The characteristic diesel "knock" occurs when fuel that has been injected into the cylinder ignites after a delay causing a late shock wave. Minimizing this delay results in less unburned fuel in the cylinder and less intense knock. Therefore higher-cetane fuel usually causes an engine to run more smoothly and quietly. This does not necessarily translate into greater efficiency, although it may in certain engines.
So you see, my statement that in certain engines it may make a small difference. With the DDE and two turbo's etc. who really knows. I think using 51 cetane as BMW recommends is a good idea, but for all we know it may decrease fuel economy as it might also increase PM emissions too.

Finally from our friends at ASTM: https://law.resource.org/pub/us/cfr/....d975.2007.pdf
Quote:
Cetane number is a measure of the ignition quality of the fuel and influences combustion roughness. The cetane number requirements depend on engine design, size, nature of speed and load variations, and on starting and atmospheric conditions. Increase in cetane number over values actually required does not materially improve engine performance. Accordingly, the cetane number specified should be as low as possible to assure maximum fuel availability.
Quote:
Originally Posted by dunderhi View Post
Anyway, my experience is that the brand of gas does not correlate to the source of the diesel. There are two Shell Stations near my home. The Shell two miles to the West is owned by a local fuel distributor. They sell Shell, BP, and their own brand of gas at their stations. I got similar mpg performance at several of their stations. Now the other Shell station, which is about two miles to the East of me, is owned by High's Dairy Stores, which is a larger, but primarily a Maryland chain. They sell Shell or Citgo gas at their various stores. The performance that I got from their diesel was consistently better than all of the other stations in my area, so I suspect they only have one source of diesel. Since all of the pumps in my area only state >40 Cetane , one doesn't know if it is 40 or 50. I strongly suspect High's Cetane level is higher than the others, but improved lubricity could also be a part of the mpg improvement.

BTW, I don't work for or own any part of High's.
The trouble I have with your analysis is that it seems that you assume "diesel is diesel" and care more about the source of the refinery than the additive package unique to each brand. I think both make a difference, but see your point. The different sources of base diesel may have different energy content - perhaps enough to make a difference in fuel economy, but also in other parameters that may indirectly affect drivability and fuel economy. Different engine technology which includes common rail direct injection and electronic engine management (DDE) also may make a difference in how a specific cetane affects fuel economy, if anything at all, since most engines are designed for 40 to 55 or so cetane anyway.

Cheers.

PL
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Last edited by Pierre Louis; 11-05-2014 at 07:58 AM.
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  #9  
Old 11-05-2014, 07:07 AM
Pierre Louis Pierre Louis is offline
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Quote:
Originally Posted by dunderhi View Post
My best tip is to try different fuel stations and keep track of you mileage. There's quite a of variation in CETANE levels. The local Highs Dairy Store chain (Shell or Citgo gas) consistently gave me an additional 2 mpgs. A different Shell station just down the road, but with locally sourced diesel, did not perform as well.
Just out of curiosity, how did you find out the cetane levels in the fuel at the different stations?

PL
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Old 11-05-2014, 07:08 AM
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Squiddie Squiddie is offline
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The block the radiator thing is a bit misunderstood. It insulates the actual engine block from the wind, and that is having an effect.

I would not be comfortable doing that without having a proper oil temperature meter, e.g. via a blutooth cellphone. The instrument cluster display is a bit too smoothed out for my taste. And it should be oil you look at, not water.
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Old 11-05-2014, 10:17 AM
Hoooper Hoooper is offline
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Oil temps are really not even a remote issue on the 335d. Guys have run track days without seeing high oil temps like the 335i guys do, so its not going to be an issue. Might be a problem if you left it blocked during a track day but that would be a silly idea anyway.
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Old 11-05-2014, 12:34 PM
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dunderhi dunderhi is offline
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Quote:
Originally Posted by Pierre Louis View Post
Just out of curiosity, how did you find out the cetane levels in the fuel at the different stations?

PL
I don't know the cetane levels other than they are above 40.
I do know that consistently that one chain of diesel stations supplied me with diesel that was one average 2 mpgs better.




Quote:
Originally Posted by Pierre Louis View Post
The trouble I have with your analysis is that it seems that you assume "diesel is diesel" and care more about the source of the refinery than the additive package unique to each brand. I think both make a difference, but see your point. The different sources of base diesel may have different energy content - perhaps enough to make a difference in fuel economy, but also in other parameters that may indirectly affect drivability and fuel economy. Different engine technology which includes common rail direct injection and electronic engine management (DDE) also may make a difference in how a specific cetane affects fuel economy, if anything at all, since most engines are designed for 40 to 55 or so cetane anyway.

Cheers.

PL
Thanks for the links, but they don't give me a warm and fuzzy that higher cetane level don't yield higher efficiency, but let's say that's my issue and not yours.

For the record, I don't think diesel is diesel which is why I researched my local diesel supply.
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