X5 e53 3.0d - Fuel Range suddenly dropped.

[Salty_Dog]

For years when we fill up the fuel tank, we've got a Range of 999km on the OBC.
Actual range is around 1050 to 1100km on country roads.

For the last year, I've noticed after filling the fuel tank, the display only shows 754km.
Driving has not changed.

I'll admit, it hasn't had a fuel filter for 6 years + or an Air Filter for 4 years.
Oil and Oil Filter every 10,000ks

Currently on 265,850 km

Any ideas?

Fill up at the same Service Station
Driving patterns haven't changed.

Thank You

[chrisfuture8]

Changing out the air filters on a regular basis is very important to getting good performance and MPG. Your air filter being 4 years old is way overdue unless it only has a few thousand miles on it since new. I typically change out the air filter every 3rd oil change (6 thousand miles per oil change). I inspect the air filter on every oil change to make sure it's still in usable condition. If I put it up to the outside day light and don't see through it, then it's time to replace regardless of mileage on it thus far.

In terms of fuel filter, my wife's X5 had 138K miles before I changed it. But before that, the car was exhibiting some strange performance problems. Car won't start after 1/4 tank left, car runs and eventually dies on the road when it fuel tank is around 1/4 full. Took me a while to recognize that pattern. Got errors that pointed to bad ignition coil, CPS sensor and fuel pump and so forth. After throwing money and replacing those parts just mentioned, it turned out to be a partially clogged fuel filter...!

Normally, on a gas engine, the O2 sensors and spark plugs should be checked as well, but since your car is a diesel, don't think those would apply. However, it has been stated that bad glow plugs on diesel engines can result in poor mileage.

[andrewwynn]

@chris: if one of the things you didn't repair was the jet pump you should look into it: the main cause of fuel starvation if under 1/4 tank is a leak in the o-ring seal going back to the left tank from the fuel filter/FPR unit. Switching the fuel pump or the FPR may boost pressure to mask the problem but won't solve the problem that is a design flaw so every one will eventually fail. See my threads about the problem and the cost free solution.


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[andrewwynn]

Mpg will be affected by plenty of things but the biggies are:

Bad plugs (I got instant 10% boost)
Thermostat (I got 15% boost)
Crappy fuel. 10 % ethanol crap


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[Salty_Dog]

Originally Posted by andrewwynn

Mpg will be affected by plenty of things but the biggies are:

Bad plugs (I got instant 10% boost)
Thermostat (I got 15% boost)
Crappy fuel. 10 % ethanol crap


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We are speaking about a Diesel here

[chrisfuture8]

Apologies in advance for hi-jacking your thread, Salty_dog.

@Andrewwynn, is this the thread you're talking about:
https://xoutpost.com/bmw-sav-forums/...stic-help.html

It took me a couple months of troubleshooting, searching, and repairing to get the X5 back on the road because of the fuel issue. After replacing 1 ignition coil, 8 spark plugs, 1 fuel pump motor, 2 CPS sensors, and finally the fuel filter, the SUV can run until the tank is literally empty. No more no start or car dies while running issues.

[nice1guv]

Fuel filter probably won't make much of a change, but after 6 years, I'd do it anyway.

Glow plugs only affect starting, so nothing in that one.

Air filter on the other hand will certainly need doing!
Diesels generally make a right mess of the air filter and quickly as well.
So I would be changing this immediately.
Your filter will be black as can be!

Thermostat can also make quite a difference to economy.
Does the temp needle get to halfway, straight up and down?
If not, then the thermostat is stuck open.

Even though it says ~750km just after filling, does it go back up after driving for a while and then still get the 1000km or so to empty?

Other possibilities: cracked exhaust manifold, do you get diesel smoke and smell on startup in the cabin or coming from under the front of the car or drivers side?
The hoses from the little vacuum tank to the turbo and the turbo waste-gate, split over time. Is the turbo making the same noise and pressure/power as usual?

[wpoll]

...and while you in there changing the air filter element, change the engine breather (PCV) too. It's critical for the health of your turbo to get rid of the old "loo-roll" filter type and replace it with the newer "vortex" design.

And I'd echo nice1guv's comment about the current MPG reading - the range is based on the current MPG reading so if it's high (as when you have been running around town) then the projected range will seem low.

But I'm guessing you know this and I'm also guessing that your issue is a real increase in fuel usage and not just a cosmetic one. I don't think I've ever seen a range of only 750km when the tank is full...

[Salty_Dog]

The old style pcv was never in the 2006 model.
But I did change it 4 years ago anyway.

Yes... I'm well used to the X5 normal range behavior in relation to driving conditions....
We have never seen 999 range for a year or more now...

First I thought it was foaming in the diesel when filling up.
But it can't be that this many times in a row

[wpoll]

All good then. My 2005 was "born" in February and they didn't make the breather change until August. The "loo roll" was utterly buggered when I pulled it...