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      05-08-2021, 04:43 AM   #1
DriveS
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335d fuel filter after 55k

Changed my oil this morning in its regular 6k change and also changed the fuel filter for the first time.....

I think the BMW schedule is 60k or more for the fuel filter, but I read it should be done more regularly.

Here is the state of the old filter.....shocking. Covered in brown sticky residue. It should be white! I can imagine this will cause a pressure drop enough to affect performance.

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Will test drive and report back.

If you have not done yours then you need to. I think every 2 years or 20k they should be changed.
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      05-08-2021, 05:12 AM   #2
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My 335d (17 plate with 20k) was in for an oil service on Thursday and they changed the fuel and air filters as part of the service package.
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      05-08-2021, 05:18 AM   #3
Craig-SM
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I thought it was 2 years or 30k miles
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      05-08-2021, 05:55 AM   #4
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I thought it was every other oil service, so 4 years max or just under 40k miles I guess.
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      05-08-2021, 06:26 AM   #5
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Quote:
Originally Posted by DriveS View Post
Changed my oil this morning in its regular 6k change and also changed the fuel filter for the first time.....

I think the BMW schedule is 60k or more for the fuel filter, but I read it should be done more regularly.

Here is the state of the old filter.....shocking. Covered in brown sticky residue. It should be white! I can imagine this will cause a pressure drop enough to affect performance.


Will test drive and report back.

If you have not done yours then you need to. I think every 2 years or 20k they should be changed.
You say you 'imagine' it will have been causing a drop in performance.

Even if you're only doing 30mpg, that filter only has to let through 150ml of diesel per mile. If you're doing 40mpg, it's only needing to put through 113ml of diesel per mile. That fuel is also not just being gravity filtered through, it's being pushed through by the high pressure fuel pump in the tank.

If it was causing fuel starvation problems (and a lack of performance), then you'd have had fault codes, engine stuttering under hard acceleration, obvious lack of power.
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      05-08-2021, 06:57 AM   #6
DriveS
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Quote:
Originally Posted by robbiep View Post
You say you 'imagine' it will have been causing a drop in performance.

Even if you're only doing 30mpg, that filter only has to let through 150ml of diesel per mile. If you're doing 40mpg, it's only needing to put through 113ml of diesel per mile. That fuel is also not just being gravity filtered through, it's being pushed through by the high pressure fuel pump in the tank.

If it was causing fuel starvation problems (and a lack of performance), then you'd have had fault codes, engine stuttering under hard acceleration, obvious lack of power.


Good points....

I am thinking about full flow rate under max acceleration on a remap...
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      05-08-2021, 08:49 AM   #7
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Quote:
Originally Posted by DriveS View Post
Good points....

I am thinking about full flow rate under max acceleration on a remap...
And how long is that ? 10, 20 seconds per minute of driving ?

Unless you're on a racetrack, you're never going to even approach the limits of what a clogged-up filter can provide - and if you are on a racetrack regularly, then you put a competition filter and fuel pump on, and be done with it
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      05-08-2021, 09:02 AM   #8
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A bit of Googling and a rough calculation:-

400HP diesel engine uses around 100 litres / hour.

which is 2 litres / min
or
30ml per second.

I wouldn't know what degree of effect that filter would have on such a rate.
It's probably not good?

Maybe there are pressure difference or flow monitoring systems which would throw codes. Maybe experience has set the change interval period.
Dunno.

Edit:
Fuel and air filters were changed on the second service (36k) of my 335d.
(Idrive service indicated).
The previous E90 325d, I think was nearer 60k. Certainly for the air filter.
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Last edited by NanasBack; 05-08-2021 at 09:10 AM..
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      05-08-2021, 10:28 AM   #9
dave550i
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You will be lucky to ever get a fuel filter changed at a main dealer in my experience with them! usually too much trouble removing the underneath covers to get to them, and most owners unless ones that get involved with spanners themselves will never know! my past bmw ownership when checked fuel filter they have had the manufactured date of the filter which corresponded with the car sometimes 4 or 5 years later and 60/70 miles, out of sight out of mind!
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      05-08-2021, 01:25 PM   #10
DriveS
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Quote:
Originally Posted by NanasBack View Post
A bit of Googling and a rough calculation:-

400HP diesel engine uses around 100 litres / hour.

which is 2 litres / min
or
30ml per second.

I wouldn't know what degree of effect that filter would have on such a rate.
It's probably not good?

Maybe there are pressure difference or flow monitoring systems which would throw codes. Maybe experience has set the change interval period.
Dunno.

Edit:
Fuel and air filters were changed on the second service (36k) of my 335d.
(Idrive service indicated).
The previous E90 325d, I think was nearer 60k. Certainly for the air filter.
I used to be a pneumatic/hydraulic design engineer. Spent many hours lab testing designs including filters. When I saw the thickness of the residue, I thought restriction could well be possible. Of course I have no evidence. Just an opinion.

I should have changed it a couple of years back.

The post is for those, like me that haven't changed it yet.
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      05-08-2021, 03:03 PM   #11
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Testing filters?
That's interesting.

BMW guidelines state, you should use no additives in the diesel fuel.
Would you think there's a possibility, some additives may dissolve part of the crap the filter gets clogged with, which then passes throug the filter and progresses to the engine and maybe then causes issues with injectors, DPF etc. ?
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      05-08-2021, 06:09 PM   #12
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Quote:
Originally Posted by NanasBack View Post
Testing filters?
That's interesting.

BMW guidelines state, you should use no additives in the diesel fuel.
Would you think there's a possibility, some additives may dissolve part of the crap the filter gets clogged with, which then passes throug the filter and progresses to the engine and maybe then causes issues with injectors, DPF etc. ?
Except, BMW do sell an additive. And fuels have additives in them anyway.
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