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      12-22-2017, 01:17 PM   #1
mayhs
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Loss of MPG after fuel filter change

I've got a BMW E90 Pre LCI 330D with just over 100k on the clock and recently had the fuel filter changed and had a pretty big drop off in MPG. The car was remapped and the DPF and swirl flaps removed by the previous owner.

Before the change I was averaging around 32-33mpg (my commute is about 15 miles with 75% relatively heavy motorway traffic with 25% with relatively heavy city traffic). This has now dropped to around 26mpg!

I figured the cold weather must have been having an effect so I've been keeping an eye on coolant temps which were around 83DegC. So I've had both thermostats changed and now sit at 91-92DegC after a short drive.

Also had all glow plugs (and controller) replaced last winter but I don't think this should have an effect on mpg to be honest.

I'm not really sure what else could be causing such a drop off in MPG. Car runs smooth and no drop off in power either.
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      12-22-2017, 04:04 PM   #2
rasa bmw
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caliper binding?,had it 3 times on my e46..one only 2 weeks ago,mpg dropped to 23 mpg now at 44 after a decent long drive and a few other trips..when they just start off binding the mpg isnt that noticeable,but once it gets proper fully binding it will rapidly reduce,,go for a drive and get a bottle of water and spray it through each wheel to determine which one.you will easily tell as the steam will tell..just a thought .
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      12-23-2017, 08:23 AM   #3
mayhs
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Quote:
Originally Posted by rasa bmw View Post
caliper binding?,had it 3 times on my e46..one only 2 weeks ago,mpg dropped to 23 mpg now at 44 after a decent long drive and a few other trips..when they just start off binding the mpg isnt that noticeable,but once it gets proper fully binding it will rapidly reduce,,go for a drive and get a bottle of water and spray it through each wheel to determine which one.you will easily tell as the steam will tell..just a thought .
Cheers for the reply, I'll definitely check that out as I had a squeaky rear brake a few weeks ago and was told that it was 'sticking'.

Thanks for the reply
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      12-23-2017, 09:11 AM   #4
Andy198712
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you can just touch the centre of the alloys as a dragging brake will heat up the alloy too...
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      12-23-2017, 03:26 PM   #5
therealdb1
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Quote:
Originally Posted by Andy198712 View Post
you can just touch the centre of the alloys as a dragging brake will heat up the alloy too...
Probably a good idea as spraying cold water onto a hot disc may cause it to warp or crack.
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      12-24-2017, 05:15 AM   #6
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Originally Posted by therealdb1 View Post
Probably a good idea as spraying cold water onto a hot disc may cause it to warp or crack.
so what if it starts to rain? a little water will have no effect.
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      12-26-2017, 11:22 PM   #7
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Quote:
Originally Posted by rasa bmw View Post
so what if it starts to rain? a little water will have no effect.
Maybe, maybe not. I have managed to warp a disc so badly that the wheel would hardly turn all the way round simply by driving through a puddle with hot brakes.
If the brake is sticking to the extent it is noticable in mpg it is likely to be extremely hot and placing the back of your hand next to the wheels will indicate the difference in temperature so why risk it?
Still they are your discs so it is up to you what you do with them.
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      12-27-2017, 04:13 AM   #8
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Quote:
Originally Posted by therealdb1 View Post
Maybe, maybe not. I have managed to warp a disc so badly that the wheel would hardly turn all the way round simply by driving through a puddle with hot brakes.
If the brake is sticking to the extent it is noticable in mpg it is likely to be extremely hot and placing the back of your hand next to the wheels will indicate the difference in temperature so why risk it?
Still they are your discs so it is up to you what you do with them.
not talking about submersing the wheel..i said spray a little water...could spit on it either as i have in the past when no water to hand..
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      01-09-2018, 02:52 PM   #9
mayhs
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Thanks for the replies. I took the car in to the garage and they confirmed I had a binding rear brake. I've had the calliper and pad changed.

However my MPG seem to have only improved marginally. Getting around 26-27MPG. I'm still putting mileage on the car and hoping this will increase but something still isn't right.

Is there a chance that BMW used the wrong fuel filter and that's having an effect? Can't understand what could be causing such a reduction. Can seems to start and run smoothly. No bouncing idle or anything like that. Only symptom seems to be reduced MPG...
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      01-10-2018, 04:14 AM   #10
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Quote:
Originally Posted by mayhs View Post
Thanks for the replies. I took the car in to the garage and they confirmed I had a binding rear brake. I've had the calliper and pad changed.

However my MPG seem to have only improved marginally. Getting around 26-27MPG. I'm still putting mileage on the car and hoping this will increase but something still isn't right.

Is there a chance that BMW used the wrong fuel filter and that's having an effect? Can't understand what could be causing such a reduction. Can seems to start and run smoothly. No bouncing idle or anything like that. Only symptom seems to be reduced MPG...
id get the codes read,,otherwise you will be throwing money at fixes on the summise its going to fix it....bm cable or carly are probably the best readers...
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      01-10-2018, 05:49 AM   #11
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Agreed, this needs proper diagnosis by a decent BMW spec bit of kit.

Is the vehicle down on power also? Something else that can have a negative effect on MPG is the large red boost hose connected to the inter cooler. Is it covered in oil?

If you stand in front of the car with the bonnet open, look down and to the left. You should see it.

It's a common issue with M57 setups.
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