# DEF refill



## Michael47 (May 9, 2014)

Well, it finally happened: I got the low DEF, 999 miles to no-start alert this morning. I'd bought the small bottle of DEF from the dealer last fall prior to our trip out west dragging a travel trailer in expectation that I might well use it then, since the trailer cuts fuel mileage down to the 14-15 mpg range. Didn't happen before oil change time, but now with 2900 miles left before the next oil change, according to iDrive, it's happened.

So I bought a 2.5 gallon jug of DEF from AutoZone, and set to. First dumped the small bottle in the active tank (that's the one up by the radiator, if I understand correctly), then I cut the bottom off the bottle to use it as a funnel. Next I opened the 2.5 gallon jug and put it's cute little pour-hose on it, and repeatedly used it to refill the new funnel and then add to the tank. That took about a gallon of DEF from the big jug for a total of about 1-1/2 gallon before she was full.

Close that, hosed down the little splatters I'd made and set to putting the rest in the passive tank, which is the one under the air hose from intake to air filter. I'm sure the gallon and a half I put in did not fill it, but should be enough to get me to the next oil change.

Whole job took me about 15 minutes, including the clean-up. So, DEF refill = no big deal, guys 'n' gals. Used the tool in the BMW tool kit and a matte knife. No other tools needed, except for safety glasses in case I waxed sloppy. And somebody got quoted $300 by a dealer for this job? Really? I'm in the wrong racket.


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## dieseltrekker (Feb 24, 2016)

People always make such a big deal with the def fluid, if you can fill your gas tank you can fill def fluid its just a different approach


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## FredoinSF (Nov 29, 2009)

I liken it to refilling windshield washer fluid, except it's a little messier and there is that darn hose in the way. No biggie though. 
I have only filled the passive tank with the full 2.5 gallons and not bothered with active tank. The pump seems to do its job every time.


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## Doug Huffman (Apr 25, 2015)

That is also my plan, to fill only the passive tank.


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## gunksny (Apr 19, 2006)

dieseltrekker said:


> People always make such a big deal with the def fluid, if you can fill your gas tank you can fill def fluid its just a different approach


The only pain is the special "nozzle" you need to get the DEF into the tanks. And removing the air intake tube to get at the passive tank can be a bit of a hassle.

Like many others here, I bought the smaller size container initially, then cut the bottom off to use as a funnel for the larger size. I went to the local VW dealer and was able to buy both sizes ($13/2.5 gal) for HALF the price than they were charging at the BMW dealer. It is EXACTLY the same stuff.


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## n1das (Jul 22, 2013)

DEF is 32.5% urea and 67.5% de-ionized water.
IIRC, the E70 X5 35d holds a grand total of 5.95 USgallons. I only fill the passive tank.

DEF is DEF is DEF is DEF is DEF....is DEF. It's all the same and brand of DEF and where to get it doesn't matter. DEF is made to an industry standard and used worldwide and is a commodity item. DEF is DEF. I get the 2.5 gallon containers of Peak branded DEF at my local Walmart* for much less than any BMW or VW dealer or any local gas station.

It is so easy to DIY and avoid paying $300 at a BMW dealer to have them do it.

Have fun!


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## Flyingman (Sep 13, 2009)

+1:thumbup:

In 6 1/2 years I've yet to try to add DEF to my 335D.  I do it all the time in my GL350. Easy Peasy when the fill port is right next to the fuel port. I still manage to dribble some when it over flows, but just rinse it down and wipe it off.

Can't comment on the 335D DEF fill, yet. Always done during service so far at the dealer.


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## Kostyan (Aug 8, 2014)

How do you guys know that your tank's been filled - do you allow it to overfill? 

Is there any damage from overfilling?


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## montr (Oct 7, 2006)

You should not overfill. If overfilling, the DEF will leak on top of tank thru the vent and may damage tank components.

I wait for the low DEF warning (the 900 miles countdown) and then I add 2.5 gallon to the passive tank. The filler neck for the passive tank is the upper one on the 335d E90.

Here is the text from SIB 160210:
"Do not overfill the SCR system. Filling the tanks up to the top of their respective filler necks will cause the DEF to leak out of the tank's vent system, and will possibly damage the tanks and internal components. All active and passive tanks are filled to the correct level at the factory. A tank level reading of 66% on a new vehicle requires no further action."


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## Doug Huffman (Apr 25, 2015)

montr said:


> You should not overfill. If overfilling, the DEF will leak on top of tank thru the vent and may damage tank components. I wait for the low DEF warning (the 900 miles countdown) and then I add 2.5 gallon to the passive tank.
> 
> Here is the text from SIB 160210:
> "Do not overfill the SCR system. Filling the tanks up to the top of their respective filler necks will cause the DEF to leak out of the tank's vent system, and will possibly damage the tanks and internal components. All active and passive tanks are filled to the correct level at the factory. A tank level reading of 66% on a new vehicle requires no further action."


Thank you very much for the SIB!!!

Here is more evidence that BMW mechanics are the cause of DEF tank failures. Previously I have noted that there is no approved procedure for filling with a nozzle-hose-pump-tank rig that will over pressurize a tank on going full due to the impulse - water hammer - of the liquid mass at speed suddenly stopping.

And now I see the caution to not (over)fill the system.

Thank you very much.


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## montr (Oct 7, 2006)

Yes, the procedure of filling up the DEF up to the filler neck is wrong and it is overfilling. There are no easy way for anyone (including mechanics) to know when the tank is full.
To me, the best approach is to only fill the DEF when the system ask for it (the mileage countdown) and putting an amount of fluid that is less than the tank capacity.


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## need4speed (May 26, 2006)

montr said:


> *you should not overfill. If overfilling, the def will leak on top of tank thru the vent and may damage tank components*.
> 
> I wait for the low def warning (the 900 miles countdown) and then i add 2.5 gallon to the passive tank.
> 
> ...


+1


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## Doug Huffman (Apr 25, 2015)

montr said:


> Yes, the procedure of filling up the DEF up to the filler neck is wrong and it is overfilling. There are no easy way for anyone (including mechanics) to know when the tank is full.
> To me, the best approach is to only fill the DEF when the system ask for it (the mileage countdown) and putting an amount of fluid that is less than the tank capacity.


Yes. That is what I took from the SIB. Drive to the warning at a presumed level and add a known volume of fluid.

_Presume_ has an interesting history, it is evidence taken as true barring indication to the contrary. (_The Science of Conjecture: Evidence and Probability Before Pascal_, James Franklin, JHU 2015)


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## MotoWPK (Oct 5, 2012)

Interesting the SIB cautions against filling the tanks up to the top of their respective filler necks but doesn't describe a procedure that will fill the tanks without filling them to the top of the filler necks.

One also can't use a measured volume fill since there are only three measuring points (A, B and C in the SIB) with no way of knowing where the liquid level is in between these points.

At about 5,000 miles I had the dealer top up our DEF tanks, which they did using a 2.5 gallon jug of DEF through a funnel, pouring a bit at a time while they peered down the funnel. On the passive tank they over did it slightly with the liquid level backing up into the funnel. When the funnel was extracted, this liquid drained into the small overflow pans surrounding the fill port and then slowly drained into the tank (the fill line clearly connects somewhat below the top of the tank and the vent line through which the overflow pan drains). The next day we left on a trip, passing through warmer weather. After the trip I discovered DEF had spilled onto the engine below (which I washed off). Clearly what happened was that the filling had left insufficient space for thermal expansion and, this being the passive tank, the system hadn't drawn any volume from the tank (the active not having needed to be replenished).

While I have yet to use them, I do have a couple of the BMW bottles of DEF. The instructions for these are to fill until the valve on the end of the bottle shuts off. This will occur when the liquid level reaches the valve, which is at, or very close to the top of the filler neck.

This implies that filling to the top of the filler neck is not an over fill, there still being volume left in the tank for expansion, but over filling the filler neck can reduce this expansion volume to the point that it is insufficient and can result in subsequent overflow.

Can't see over filling by gravity damaging the tank, but filling with a pump could have that potential.


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## Doug Huffman (Apr 25, 2015)

IIRC the tank vents are airstone like and may clog if wetted.

Would not 2.5 gallons in the passive tank from the warning point in the active tank be reasonable? SIB 16 01 09 that extracted remaining DEF to empty also says that only 2.5 gallon service bottles will be reimbursed warranty. The lack of precise directions to the mechanics may be an unintended consequence of the extraction procedure being obsoleted.


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## MotoWPK (Oct 5, 2012)

Doug Huffman said:


> IIRC the tank vents are airstone like and may clog if wetted.
> 
> Would not 2.5 gallons in the passive tank from the warning point in the active tank be reasonable? SIB 16 01 09 that extracted remaining DEF to empty also says that only 2.5 gallon service bottles will be reimbursed warranty. The lack of precise directions to the mechanics may be an unintended consequence of the extraction procedure being obsoleted.


Not familiar with 'airstone like' vents, but wetting of the vent lines seems inevitable to me since they are also an overflow line and even without an overflow, I expect at least the lower portion of the vent must be wetted due to the DEF moving around from vehicle motion, at least when the tank is full. Even if the vent does become blocked by DEF crystals, the fill line, which is much larger, also provides venting, assuming it is not filled with liquid, of course (the fill port cap does not seal tightly by any means, at least not on my '14 X5 35d).

I expect 2.5 gallons in the passive tank from a low level warning (miles remaining) would not result in an overfill. First, it's my understanding the low level warning is only triggered by the active tank sensors, and one would only arrive at this point after the passive tank has been depleted refilling the active tank. I expect the system does not drain the passive tank to zero (wanting to keep the pump and associated plumbing filled with liquid), but close enough that it would accept 2.5 gal in the passive tank's 3.4 gal capacity. Of course upon restart the passive tank would quickly be depleted as the system transfers DEF from the passive tank to the active tank.

I, for one, don't want to limit myself to a range corresponding to 2.5 gal. While I prepare for the possibility of having to replenish the system on a road trip by carrying a couple of the BMW 0.5 gal DEF bottles, I prefer to have sufficient DEF in the system at the outset that I don't have to bother with refiling in the middle of a trip.

When I purchsed our X5 I initially I planned on the 10,000 nominal range indicated by BMW. With a total capacity of 7.7 gal in the '14 X5 35d, that would equate to a DEF mileage on the order of 1300 mpg. I've been tracking the actual usuage over ~30,000 miles now (at least as closely as I can), and the actual DEF mileage has averaged about 3200 mpg, for an absolute DEF range of over 24,000 miles. This also equates to a DEF/diesel consumption ratio of ~0.9%.

I'm somewhat surprised at how low the DEF consumption is and wonder if the recent EGR A reprogramming recall 13-01-16 is lowering the EGR rate to shift more of the NOx reduction to the SCR, with a corresponding increase in DEF consumption. Perhaps based on real world experience, BMW has realized they can rely more on the DEF for NOx reduction, while maintaining the required DEF range, reducing the potential for CBU by reducing the EGR rate.


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## montr (Oct 7, 2006)

In the E90, there are two vents, one is the filler vent and the other one is on top of the passive tank. The filler neck and the filler vent are next to each other and both are above the second vent on top of the passive tank. The filler vent is sealed when you the filling cap is back on.

The passive tank vent is vented to the outside, has a filter and is lower than the filler neck. When the DEF reach the top of the filler neck, you are above the passive tank vent and DEF will overflow on top of the tank.

Here is text in page 85 of "ST810 - Advanced Diesel Technology Workbook"
*Venting*
The passive reservoir is equipped with one operating vent (2 in the E90) and one filler vent. The operating vent is directed into the atmosphere. A so-called sintered filter tablet ensures that no impurities can enter the reservoir via the operating vent. This sintered tablet consists of a porous material and serves as a filter that allows particles only up to a certain size to pass through. The filler vent is directed into the filler pipe and therefore no filter is required.

Note: The E90 DEF filling is poor design. BMW should have done a more user friendly system.


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## floydarogers (Oct 11, 2010)

montr said:


> ...
> Note: The E90 DEF filling is poor design. BMW should have done a more user friendly system.


I agree. They fixed it for the F30 - a single port beside the fuel filler.


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## Flyingman (Sep 13, 2009)

montr said:


> In the E90, there are two vents, one is the filler vent and the other one is on top of the passive tank. The filler neck and the filler vent are next to each other and both are above the second vent on top of the passive tank. The filler vent is sealed when you the filling cap is back on.
> 
> The passive tank vent is vented to the outside, has a filter and is lower than the filler neck. When the DEF reach the top of the filler neck, you are above the passive tank vent and DEF will overflow on top of the tank.
> 
> ...


Think after thought on their part. The E90 was already well thought out without use of DEF in the diesel (European Model). They threw the US version into the mix and they had to work round with what space they had without a major redesign. Plus don't forget the German Engineers would never have to actually use it in their own cars. Kinda like those coffee cup holders!:thumbup:


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