[TEF]

I am at 23K miles with my 2016 X3 diesel and heading towards my third oil change. While oil consumption between changes is virtually zero, I have received low-DEF warnings shortly after oil changes at 10K and 20K. The first change was done by my dealer, BMW of Cleveland, and the second by the BMW in Idaho Falls. I am inclined to believe that US dealers service so few diesels that they often forget to add DEF with each oil change, but each indicated the addition of DEF on their respective service invoices. A third BMW dealer, adding DEF between the 10 and 20-thousand mark, claimed there was no leak in the DEF tank or system. So if DEF was really added with each oil change and the system is fine, where's it going?

I should add that I've just concluded a 5,000 mile cross-country trip and the vehicle worked flawlessly.

[one 35i]

It is burnt off as you drive. It helps cut emissions. In my MB I used about 5 gals of DEF every 7-8k miles.

[TEF]

I am well aware of the fact that it's consumed while driving, but the tank is of sufficient capacity to last for at least 10K miles (the period between oil changes). In my case, it is running out after driving much less than 10k miles, so my question is why. Is there a problem with the DEF system or are the dealers forgetting to fill the tank with each oil change? Has anyone else experienced this problem?

[Scout10]

If the owner were to monitor the level before it goes for oil change.
And checks level again after oil change, that solves part of the question.

Then knowing what the level is after oil change he can then determine
usage rate for his vehicle based on miles driven after oil change
You said you were well aware of the fact it gets consumed.
How much gets consumed ???????
more in winter than summer ???????

[TEF]

Unlike the oil level that can be monitored on screen, there is no way of checking whether DEF tank is empty or full. Therefore, one cannot measure consumption. Furthermore, customers are rarely allowed into the dealer's service bay, so one must take their word that sufficient DEF (or any at all) is actually added during an oil change and that all is well with the DEF system. What is known is that the tank is large enough to supply enough DEF between oil changes every 10K miles and twice it has come up empty between oil changes. However, I am thankful for One 35i's comment because it does provide some idea typical consumption and how large the DEF tank is likely to be.

[TEF]

After visiting a third BMW dealer today, it seems that DEF consumption is fine, however, with each oil change (at 10K and 20K miles) the previous dealers forgot to refill the DEF tank. Today's dealer added about three gallons and indicated that the tank was almost empty.

[Eaglesview]

I was told the DEF capacity was 22 litres. There are two tanks and when the first one runs out the DEF alarms comes up.

DEF can damage the paint if not flushed off immediately. I had the DEF alarm just before my third oil change. I suspect the dealers are not completely filling the tanks during service but just opening a couple of what look like2 gallon containers and guessing that will be enough to get you to the next oil change and they have avoided the risk of over fill and cleanup.

I have wondered if it would be possible to go to a truck stop and use their fill DEF pump. Problem would be cleanup of any spill.

[TEF]

On the X3 and 5 series, the DEF filler port is next to the fuel filler cap. Filling this port does not look easy unless on has one of the those DEF bottles that screw onto the DEF port. On the X5, one can use a funnel and pour DEF into each of the two filler ports, however, this seems a much messier prospect with those located next to diesel filler cap. If it's as corrosive as you've said, it might be good to adapt an empty DEF bottle for the purpose. However, truck stops sell DEF at a fraction of what one might pay (by the 2-liter bottle) at the BMW dealer.