Diesel X5: Tips to improve MPG?

[11_335D]

So long story short, my 2014 X5 35D with ~184k miles has shown a decrease in MPG. I use to get ~32-34 mpg with 25/75 driving, now I'm getting ~27-29 MPG. I do the normal 10k oil changes and 20K fuel filter changes. I'll occasionally throw in a can of Liqui Moly Diesel Purge and Super additive but don't see any real improvement beside better acceleration due to the increase in cetane. I clean/check the engine air intake filter on a yearly basis. Other than that I just drive the thing 20-25k miles a year. I'm pretty familiar with gasoline motors when mpg drops, basic tune up ie spark plugs, wires, rotor, distributor cap etc. Is there something to improve for diesels? I'm guessing maybe the O2 sensors could be replaced although I'm not getting any faults for it? Anyways just seeing what others are doing besides the obvious.

[turboawd]

Tire pressures ok?
Maybe the injectors aren't atomizing like they used to? Try a cleaner in the fuel?
Could be winter diesel blend?
Have you had any issues with your x5 with all those miles?

[x5wntd]

184k miles, such a good lifetime indicator! hope my car will make it lolz

[CatalinP]

I bet you DPF is the culprit. You might want to replace it, as it should be fully clogged at this milage.

[F15GorDe]

Yep, you’re due for a new DPF at least. Seem to remember a 150k-200k replacement interval on those. Find someone that can run some diagnostics.

[devlinsky]

Originally Posted by CatalinP

I bet you DPF is the culprit. You might want to replace it, as it should be fully clogged at this milage.

99.99% this

[devlinsky]

Originally Posted by F15GorDe

Yep, you’re due for a new DPF at least. Seem to remember a 150k-200k replacement interval on those. Find someone that can run some diagnostics.

Not necessarily new, depending on the condition it might be enough to code one out and code it back in - that will reset the counter and restore the performance.

[///d]

New DPF, or delete all together.

Could probably use a carbon cleaning at that age as well.

Otherwise typical maintenance items like fuel filter, injectors, etc depending on how long its been since you went through everything.

[Clifton]

Amazing mileage on that rig!!! With a 4 year old X5d and 30k on the clock, you give me hope of longevity.


Agree with what others stated, but I'd start with the cheap fixes first:

• Tire Pressures? (I like 2-3lbs above door jamb sticker)
• Try different Gas source for a couple of tanks
• Liqui-Moly SUPER DIESEL ADDITIVE (regular use could be good for a bump 1-2MPG)
• Lighter oil weight - O-30w Oil (standard 2017 and up)
• Time for new tires? Or did you switch to softer tires?

Just as a data point, I have factory Pirelli Run flats on 20" wheels and I've averaged a total of 29MPG for 30K miles.

[11_335D]

Originally Posted by Clifton

Amazing mileage on that rig!!! With a 4 year old X5d and 30k on the clock, you give me hope of longevity.


Agree with what others stated, but I'd start with the cheap fixes first:

• Tire Pressures? (I like 2-3lbs above door jamb sticker)
• Try different Gas source for a couple of tanks
• Liqui-Moly SUPER DIESEL ADDITIVE (regular use could be good for a bump 1-2MPG)
• Lighter oil weight - O-30w Oil (standard 2017 and up)
• Time for new tires? Or did you switch to softer tires?

Just as a data point, I have factory Pirelli Run flats on 20" wheels and I've averaged a total of 29MPG for 30K miles.

Yes it's actually very impressive, it does slightly better than my 335D which is a much smaller vehicle.

I do agree with the general consensus about the DPF maybe in need of replacement but at $3k for the part alone is rather steep. A member mention a delete, as much as I would love to have the added power and emissions equipment gone. I can't tolerate the smell and I use this vehicle to haul the family. I've seen a couple videos of DPF cleanings so I may look into that this spring/summer.

I think fueling is important, I prefer getting diesel at my local Shell station that has dedicated 18 wheeler pumps so I know they are in constant supply of fresh diesel. I'm actually on my 3rd set of non run-flats all season tires (275f/315r). Tire pressure is always on the higher end of the scale due to highway driving. I've even tossed in a can of diesel purge and super diesel additive earlier today for good measures.

I have no clue what my lifetime avg mile is since I always hit the reset button after every fill up.

[W37V]

It could be also bad fuel injectors.

Essentially anything that could impede the performance of the vehicle could be a culprit. If you have less power, you will be pushing and holding pedal longer thus using more fuel.

Given the mileage, you can look into the usual things:
Any obstructions to intake
any obstructions to exhaust
any obstruction to fuel
failing turbo

[M5_1of400]

Also check your thermostat, if it is bad and coolant doesn't reach proper operating temps that's a big MPG killer.

[11_335D]

Originally Posted by DieselDemonDM

Also check your thermostat, if it is bad and coolant doesn't reach proper operating temps that's a big MPG killer.

Good point on the thermostat, I went in the hidden access menu in the gauge cluster and watched the ECT the entire drive to work. It stayed in the 88*C- 90*C range the whole drive(43*F outside temp and 70mph). Thermostat is still good.

Update:
I have my first check engine light, DTC E12C03 which is "right fuel level sensor: short to circuit b+". This is something I may have been dealing with for a year now but hasn't shown its self until now. So I remember in the past I would fill up and the needle would SLOWLY reach full on the gauge cluster. I never paid too much attention until now. So using the access menu again I can watch the fuel tank level sensors resistance values fluctuate as I'm driving. I don't see any issues with the values currently as the tank its 3/4 full but I will continue to monitor as I approach nearly empty and fill up again. I'm guessing due to the potential mismatch between the left and right fuel level sensor. The vehicle computer cannot determine the correct level of fuel in the tank when "empty" and I may be prematurely fueling when in fact I could potential go longer hence the current MPG number? Anyway just throwing out ideas before I replace this level sensor.

[andreigbs]

Originally Posted by 11_335D

Update:
I have my first check engine light, DTC E12C03 which is "right fuel level sensor: short to circuit b+". This is something I may have been dealing with for a year now but hasn't shown its self until now. So I remember in the past I would fill up and the needle would SLOWLY reach full on the gauge cluster. I never paid too much attention until now. So using the access menu again I can watch the fuel tank level sensors resistance values fluctuate as I'm driving. I don't see any issues with the values currently as the tank its 3/4 full but I will continue to monitor as I approach nearly empty and fill up again. I'm guessing due to the potential mismatch between the left and right fuel level sensor. The vehicle computer cannot determine the correct level of fuel in the tank when "empty" and I may be prematurely fueling when in fact I could potential go longer hence the current MPG number? Anyway just throwing out ideas before I replace this level sensor.

I always do manual calculation of fuel economy figures, which are always 1-2 MPG lower than computer's estimate.

Start there: manual math and confirm your real figures for a few tanks.

[Clifton]

Originally Posted by andreigbs

I always do manual calculation of fuel economy figures, which are always 1-2 MPG lower than computer's estimate.

Start there: manual math and confirm your real figures for a few tanks.

This +100 - My onboard computer is always 2 MPG above the true math. That is why I use an app like Fuely to help log the actual and historical.