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Discussion Starter #1
A while back highway mpg went from 33-35 down to 25 on a trip to Vegas. We replaced the fuel filter and air filters, and it has gotten better but still taking long trips and struggling to break 30 on the highway. Did we miss something? What else needs to be serviced? Car has 93k miles now.

Also does the type of number 2 diesel really matter? Sometimes use the cheap gas stations, sometimes 76, rarely use shell or chevron. I know with gasoline the quality of the gas being used over a period of time is more consistent and better for the car, is diesel the same way?
 

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2006 e320 CDI Williamsburg, VA
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It will be interesting to see what others have to say about this. My 2006 cdi fuel mileage seems to be dropping with me. I thought that in the summer that it would get better mileage, as diesels like the hot weather. I have been using BP with a pump listed cetane rating of 40 minimum. I am paying $.07 cents a gallon more than other stations at the BP station. I also use approximately 12 ounces of diesel kleen every other tank. My cdi has approximately 78k miles on it.
Mike T.
 

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2006 E320 CDI
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It will be interesting to see what others have to say about this. My 2006 cdi fuel mileage seems to be dropping with me. I thought that in the summer that it would get better mileage, as diesels like the hot weather. I have been using BP with a pump listed cetane rating of 40 minimum. I am paying $.07 cents a gallon more than other stations at the BP station. I also use approximately 12 ounces of diesel kleen every other tank. My cdi has approximately 78k miles on it.
Mike T.
I have never seen a great deal of difference in mileage between number 2 diesel (Min Cetane 40 or the stuff labeled Premium) from different sources. I have been driving diesel Mercedes Benz for years. You will see a decrease in cold weather because the engine doesn't run as efficiently and most diesel in colder areas is blended to perform better in the cold weather which in some cases means it has less energy content if they are blending Number 1 and 2 rather than adding an additive to reduce the cloud point. I also use Diesel Kleen but really can say it improves the mileage over just straight Number 2 diesel. I you are really seeing a significant decrease in mileage I would check the thermostat to see if it is ok. If the engine is not reaching operating temp then your mileage will suffer. Besides what I have already mentioned has anything else changed? Changed grade of oil? Different tires?
 

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2006 e320 CDI Williamsburg, VA
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Besides what I have already mentioned has anything else changed? Changed grade of oil? Different tires?
Thanks Edwin. I did not mean to hijack Micky's posting. I changed the thermostat last year and it is reaching temperature, same oil, Mobil 1 ESP, and the same tires. I only thing that was done recently was the brakes and rotors changed by my indie. It may be in my head but I do feel a slight vibration through the steering wheel. I am thinking that when (or if) they beat the old rotors off, they may have damaged a wheel bearing. My car is due for inspection during August so I will have them check it out.
On another note, I see that you are from NOVA. I just moved this past December from Kingstowne (about three miles from the Springfield Metro. FYI, below is what I have been using to keep track of my mileage. The columns are in order by date, mileage, gallons, costs, tank mileage, and miles per gallon. With me doing a little more of interstate travel, it should be averaging 32/33 mpg.


1/8 70278 14.8 55.80 450 30.4
1/19 70629 11.6 43.60 351 30.3
2/4 71214 19.4 72.25 585 30.2
2/22 71760 17.8 68.75 546 30.7
3/17 72298 18 72.90 538 29.9
3/25 72868 17.5 71.00 570 32.6
4/8 73423 17.6 71.30 555 31.5
4/27 73892 16 63.70 469 29.3
5/14 74466 18.7 72.65 574 30.7
5/30 75030 19.1 72.60 564 29.5
6/15 75565 17.9 65.25 535 29.9
7/3 76124 19 66.55 559 29.4
7/12 76687 18.3 66.00 563 30.8
7/23 77214 17.2 63.45 527 30.6

Mike T.
 

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Discussion Starter #5
Maybe going from 76 to cheap low grade diesel stations is a bad idea all to save 10 cents right? I think ill use shell for a while and see if sticking with one brand makes a difference, also running some techron through it..

How do i find out about the cetane levels?
 

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W212 M276 DELA 30 ; W211 OM642 ; R107 M117, W163 M112 E32
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I pretty much run BP 45-47 Cetane all the time that I get here in Nova. My fuel mileage has been ok, but has never been phenomenal. I've only broken a 30mpt average once or twice (I calculate at each fillup and don't listen to the computer). I do have a bit of a lead foot, have the pano roof (read: extra weight), a tuning box, 18-inch wheels and sit in DC area traffic a lot. I've never driven a 100% highway road trip except when I first bought the car and drove back from Atlanta, unfortunately I relied on the computer then.

My average when commuting from tysons corner to Springfield and back every day was between 27-28.5. I now work 3 miles from home in Tysons and spend a lot of time doing city and have dropped below 24 occasionally for a tank. Car is regularly serviced with synthetic 229.51 oil, trans fluid has been flushed twice in it's 66k history and I've also changed the fuel filters on a regular basis.

How do those numbers stack up to others?
 

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Maybe going from 76 to cheap low grade diesel stations is a bad idea all to save 10 cents right? I think ill use shell for a while and see if sticking with one brand makes a difference, also running some techron through it..

How do i find out about the cetane levels?
In certain states (like virginia),the minimum Cetane rating (as well as octane for gasoline) has to be displayed on the pumps, along with a certification date.
 

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I'll average 33-36 miles per gallon on a trip with a lot of highway miles. The average for the last 59,000 miles based on the computer is 30.9 miles per gallon. Best I have ever reached was 36 and change on an all highway trip. The 92 degree thermostat helps, but mostly it eliminated the black smoke problem I had.

I rent a lot of cars and real life fuel economy of regular cars is surprisingly low by comparison. A few months ago, a Jeep Liberty was at a surprisingly low 16 mpg for about 800 miles. More recently a Toyota Camry was in the 20-21 range. The Nissan Altima of all things faired a little better the other week at 24 mpg. Based on these numbers I can't complain at 34 miles per gallon with the Benz.
 

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I'll average 33-36 miles per gallon on a trip with a lot of highway miles. The average for the last 59,000 miles based on the computer is 30.9 miles per gallon. Best I have ever reached was 36 and change on an all highway trip. The 92 degree thermostat helps, but mostly it eliminated the black smoke problem I had.

I rent a lot of cars and real life fuel economy of regular cars is surprisingly low by comparison. A few months ago, a Jeep Liberty was at a surprisingly low 16 mpg for about 800 miles. More recently a Toyota Camry was in the 20-21 range. The Nissan Altima of all things faired a little better the other week at 24 mpg. Based on these numbers I can't complain at 34 miles per gallon with the Benz.
Checked my average today based on the computer for approximately 9000 miles and it is 30.3 mpg. That is mostly commuting to and from work and running errands on the weekend. I have taken occasional highway trips where the computer mileage has been up to 42 mpg. The annual trip to the Outer Banks was over 41mpg from Montclair, VA to Corolla, NC.
 

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2007 E320 Bluetec purchased 9/12 with 62000 miles
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My numbers were getting worse since I bought the car last month. I had been filling up at mom and pop stations, and then a Hess. From purchase, I had dropped from a reliable 37 to a hard to get 34, usual 33, all with gentle highway driving. Then Monday morning I added 10 gal, to my empty tank, of Shell diesel, and noticed it was 45 Cetane. Right after that I got 39.5 mpg on a 30 mile trip one way, highway, that was slightly down hill overall. I was elated. coming back i got 36.5, less due to uphill, headwind and traffic. That got me wondering, and sure enough the mom and pops were selling me 40 Cetane. I feel sure the 5 point diff in Cetane made a 2~3 at least mpg difference. I don't know what the Hess was, but it didn't seem to improve after it. Shell or 45 Cetane for me from now on. And the Shell was actually 6¢ cheaper!
Appended----
This morning it took a long time to get above 33mpg on the way to work. Not till about 12 of the 25 miles had gone by did the mileage break 33, even though it was almost all highway. It finally peaked at 36.5. Much worse than above. The weather was warm, about 65, and the humidity was high, and there was some drizzle on the wet roads. However I think part of the reason was that my engine temp stayed around 150 for about those first 12 miles. If you have a stuck open thermostat, it's going to hurt your mileage by keeping your engine temp too far below 180F. Going home today my engine temp was much higher, even above 180, in city driving. I think I need a need a new thermostat.
 

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I have found no difference with BP 45 cetane and everything else. Where in VA did you find shell 45 Cetane? BTW, my average is horrible. Last tank was 26 MPG, but I drive in beltway traffic everyday, have the car chipped and run 18" wheels.
 

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A couple of months ago, coming from Aspen to Glenwood Springs the computer mileage read 48.7. Of course that's downhill in thin air and the turbocharger was doing it's thing. The rest of the day on I-70 mileage dropped back to a more usual 33 to 34 going 75 mph. I'll get 37 to 38 going 70 early in the morning, and by 10 or so it's dropped back to 34. I think most of it's wind and how much the a/c compressor runs.
 

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Is it possible that the winter blends are here early which cuts down a bit on MPG?
 

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I have found no difference with BP 45 cetane and everything else. Where in VA did you find shell 45 Cetane? BTW, my average is horrible. Last tank was 26 MPG, but I drive in beltway traffic everyday, have the car chipped and run 18" wheels.
There is a Shell station at Potomac Mills mall in Woodbridge, VA that has the 45 cetane diesel. Currently $3.95
 

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I usually fill up at my local BP station as their two diesel pumps had 45 cetane stickers on them. The stickers were pretty old and faded. Within the past month I have noticed newer 40 cetane stickers on them. This BP station was charging approximately $.05 more for a gallon of diesel. It looks like now I will be shopping for price as all I can find are pumps with 40 cetane listed on them.
I do have a shell station located within eight miles of me that offers a $.10 discount on Mondays. This gets into another topic in which I would use approximately 1/2 gallon of diesel to go to the shell station and return. At a price of $3.90 per gallon, the 1/2 gallon of fuel to go to the shell station and back would cost me approximately $1.90. Factor this in to filling with approximately 15 gallons of diesel, it makes no sense to travel the extra distance to the shell station to save the $.10.
Just my $.02!
Mike T.
 

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before outside temps dropped recently I was getting average 30-31mpg city/hwy ('05 CDI )just driving around locally.. adding 1/4 of bottle of RedLine 85+ at each fill up at lowest price pump,
but noticed drop not to long ago & began to think toward fuel quality till realized that engine getting to operational temps to slow.. so next step replacing thermostat(awaiting delivery from AutohausAZ) hopefully MPG will go Up after fix.
Current diesel prices between $3.89 and $4.09 pretty much all pumps in Greater Cincinnati area having 40 cetane stickers.
 

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Just checked GasBuddy.com wow.. what a price drop since yesterday.. $3.47 now in 3 local zip codes.
 

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I have found no difference with BP 45 cetane and everything else. Where in VA did you find shell 45 Cetane? BTW, my average is horrible. Last tank was 26 MPG, but I drive in beltway traffic everyday, have the car chipped and run 18" wheels.
Beltway traffic, with all that construction also, can be worse than "city" driving. I forget what the city rating is on ours, but i think its 26. Hwy is 37, and i seem to need 45 cetane and 180°F to get it. My 16" wheels are fitted with 225/55R16 95H treadwear 740, temperature A, traction A. The overall diameter works out to 16"+(.55x225mm x 2) = 25.72", pumped to 35psi. Your 18s may be wider and flatter. wide tires hurt mileage a little at higher speeds. Mine are fairly new; have about 10K on them. To get these numbers, (36-39) I have been using C mode, and being very gentle in accelerating, going 55~70 as traffic permits, smooth, pure interstate driving, no A/C. Stock chipping. I don't yet have any long term averages. Don't know what shape my air filter is in, but I think it was changed once. In town traffic I get anywhere from 26-30, depending on the lights, but it's not super heavy traffic. Little if any A/C this time of year.
 
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