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      04-28-2014, 08:47 PM   #1
BMW_Diesel_Owner
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Diesel Exhaust Fluid (DEF) - To drain or not to drain

Do we need to drain the Diesel Exhaust Fluid (DEF)? I was advised that we should drain it completely, and then replace it with brand new fluid. My vehicle has over 100K of mileage on it.

Is it necessary? As per the vehicle's design, DEF is used after combustion, so I don't see the point of why we need to replace the fluid. I understand why we need to have the DEF fluid, but throwing away what I currently have for the sake of having a new batch doesn't make sense to me.

Thoughts?
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      04-28-2014, 10:58 PM   #2
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I have heard as it gets old it crystallizes and that is the reason you should drain it....I have never had an issue myself though and I do not drain it.
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      04-29-2014, 09:56 AM   #3
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AFAIK BMW don't do it anymore. Obviously, for them cost cutting is the first priority, but nevertheless.
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      04-29-2014, 07:44 PM   #4
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I had asked the same question on another post and the unanimous response was no, but who can you trust?
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      04-29-2014, 11:59 PM   #5
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there was an updated bmw bulletin i read somewhere that states they no longer drain the remaining fluid...simply top it up.
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      05-01-2014, 06:55 AM   #6
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How do the 2 reservoirs work? Does the vehicle use the active reservoir first (the one located on the passenger side), and then give a warning message when it starts using the passive reservoir (the one located on the driver side, under the air intake)?
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      05-01-2014, 08:00 AM   #7
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Quote:
Originally Posted by BMW_Diesel_Owner View Post
How do the 2 reservoirs work? Does the vehicle use the active reservoir first (the one located on the passenger side), and then give a warning message when it starts using the passive reservoir (the one located on the driver side, under the air intake)?
The X5 uses DEF from the active tank and fills it up from the passive as needed to keep active tank filled. IIRC, the warning sign comes when the level in the active tank is low (and the passive tank is empty or the transfer pump is not working).

I plan to keep both tanks filled up (filling both of them up every 5,500 miles or so) and not wait for the tanks to empty. My thinking is that as the levels go down in the tanks, it leaves residual DEF on the tank walls, which then dries and crystallizes and over time falls down on the bottom plugging things up. Don't know if this will work, but I've seen this happen in industrial applications with other chemicals.
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      05-01-2014, 02:10 PM   #8
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The passive tank is the one under the intake tube on drivers side? If so is there any issue in only filling up the active more accessible tank near passenger side? Do the two tanks not simply overfill into each other? I have only filled the tank on passenger side.
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      05-01-2014, 06:35 PM   #9
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Quote:
Originally Posted by BMW_Diesel_Owner View Post
How do the 2 reservoirs work? Does the vehicle use the active reservoir first (the one located on the passenger side), and then give a warning message when it starts using the passive reservoir (the one located on the driver side, under the air intake)?
Under most circumstances the active tank is keep pretty much filled by transferring DEF from the passive tank. You will receive a warning once the passive tank is empty and the active tank reaches a certain level to remind you to fill them. If the SCR system is not operating properly to met emissions standards - that is another issue and causes an "Incorrect Exhaust Fluid" warning. This should not be ignored and should be addressed by your dealer straight away.
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      06-30-2014, 02:42 PM   #10
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Does this sound like normal def fluid usage?

In the last 10k miles i have filled the truck with 4 gallons of def fluid. The first three times i used the 1/2 gallon bottles from dealer three different times after light to add def fluid came on. The most recent time the light came on i wated until the warning dropped to about 350 miles left b4 empty and used the entire 2.5 gallons jug i purchased online.

I would estimate that in the last 4k mikes i have used at least one gallon of def per 1k miles.
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      07-10-2014, 04:04 PM   #11
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Quote:
Originally Posted by Da M3nace View Post
Does this sound like normal def fluid usage?

In the last 10k miles i have filled the truck with 4 gallons of def fluid. The first three times i used the 1/2 gallon bottles from dealer three different times after light to add def fluid came on. The most recent time the light came on i wated until the warning dropped to about 350 miles left b4 empty and used the entire 2.5 gallons jug i purchased online.

I would estimate that in the last 4k mikes i have used at least one gallon of def per 1k miles.
that seems a bit high. and by bit i mean really high.

fyi get the def from vw dealer. at least around here (northern CA) it's a fraction of the cost of the bmw dealer. I got both the 1/2gal and 2.5gal for $25.
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      01-07-2015, 07:27 PM   #12
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what is the part number for the DEF fluid?
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      07-17-2015, 09:31 PM   #13
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Quote:
Originally Posted by finnbmw View Post
The X5 uses DEF from the active tank and fills it up from the passive as needed to keep active tank filled. IIRC, the warning sign comes when the level in the active tank is low (and the passive tank is empty or the transfer pump is not working).

I plan to keep both tanks filled up (filling both of them up every 5,500 miles or so) and not wait for the tanks to empty. My thinking is that as the levels go down in the tanks, it leaves residual DEF on the tank walls, which then dries and crystallizes and over time falls down on the bottom plugging things up. Don't know if this will work, but I've seen this happen in industrial applications with other chemicals.
I plan on doing the same. I just had my DEF tank replaced today under extended warranty as the check engine light came on. BMW says a low freq throttle valve and active tank faults.They found the heater had failed and was all gummed up.So I to am thinking the residual dries and crystallizes plugging things up.
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      11-22-2015, 03:09 PM   #14
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Quote:
Originally Posted by Diesel X5 View Post
I plan on doing the same. I just had my DEF tank replaced today under extended warranty as the check engine light came on. BMW says a low freq throttle valve and active tank faults.They found the heater had failed and was all gummed up.So I to am thinking the residual dries and crystallizes plugging things up.


OK everyone, I have a 20111 X% diesel and my question is;

When you replace/refill the fluid does it automatically reset the seńsor or do you have to have a resort tool?

Thanks!
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      11-23-2015, 06:30 PM   #15
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There's nothing to reset
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