2016 BMW 535d - DEF Usage

[wavinwayne]

When I purchased my 535d in 2023, it had just been serviced at the local BMW dealer, and they had topped up the DEF tank during the service. The car will give you a warning when it needs the DEF tank refilled, along with a 1k mile countdown to no-start if you don't add DEF. I wondered how long it would be until the DEF needed a refill. Since purchase in Sep 2023, I have driven roughly 20k highway miles and the 1k mile add DEF warning just popped up this week. I just added 2.5 gallons of DEF, which should hopefully get me another 20k highway miles. Honestly I don't know the DEF tank capacity and for some odd reason, there is no way to check the DEF level on my car; there is on other BMW diesels through the iDrive menu, but that option isn't available on mine for whatever reason. Just thought I would post this for anyone who's ever wondered how much DEF a BMW diesel car uses.

 

[Highlander 1459]

you can figure about 50 gallons of diesel to 1 gallon of DEF in a heavily loaded diesel as normal use. in a lightly loaded engine like in a car consumption will be lower.

 

[edyvw]

It must be more than 2.5gal.
My 2013 X5 35d had an active tank of 1.6gal and a passive tank of around 4.5gal.

 

[OneLonelyBurrito]

I would guess that it's larger than 2.5gals cause only using 2.5 gal per 20k miles would be abnormally low DEF consumption.

One thing to note, I would expect BMW diesel's to use less DEF than other diesel vehicle since it also uses a LNT (Lean NOx trap), which help reduce NOx, i.e. DEF consumption. According to the EPA benchmarking data on a 2015 BMW N57, the LNT was able to reduce engine out NOx pretty significantly at lower engine speed and load, as you can see below. So if your driving your car in an area of the engine map where the LNT is very effective at reducing NOx, it can probably reduce your DEF consumption by a decent bit compared to other diesel engines.

 

[wavinwayne]

@OneLonelyBurrito Since almost all my driving is 75mph (very low RPMs) on the highway to and from work, I'm guessing my DEF use is on the very low end of the scale.

Also, I looked in my owner's manual about adding DEF and it says when the light comes on to add three bottles of BMW DEF, which amounts to 1.5 gallons. But it doesn't say what the DEF tank capacity is. I've read somewhere that it can be a bad idea to fill the DEF tank up to the top of the filler neck, but not really sure why.

 

[OneLonelyBurrito]

Since almost all my driving is 75mph (very low RPMs) on the highway to and from work, I'm guessing my DEF use is on the very low end of the scale.

Driving down the highway appears to produce hardly any engine out NOx, so the LNT & SCR probably hardly have to converter any which would explain the low DEF consumption.

Also, I looked in my owner's manual about adding DEF and it says when the light comes on to add three bottles of BMW DEF, which amounts to 1.5 gallons. But it doesn't say what the DEF tank capacity is. I've read somewhere that it can be a bad idea to fill the DEF tank up to the top of the filler neck, but not really sure why.

That's odd it doesn't say the DEF tank capacity. But filling the DEF tank all the way up the filler neck is bad because it freezes below 12 degree F, so the DEF needs somewhere to expand too when it freezes.

 

[Dr_Dr3i]

It's probably a 5-7 gallon capacity system. As edyvw points out, there are two tanks, an active and passive. There are also heaters for the tank and for the lines so that in winter the DEF does not freeze. However, those heaters can be problematic and expensive to replace if they fail.

FYI, you can get premium DEF at Tractor Supply for cheap.

 

[wavinwayne]

It's probably a 5-7 gallon capacity system. As edyvw points out, there are two tanks, an active and passive. There are also heaters for the tank and for the lines so that in winter the DEF does not freeze. However, those heaters can be problematic and expensive to replace if they fail.

FYI, you can get premium DEF at Tractor Supply for cheap.

To the best of my knowledge, my 2016 535d has only one DEF tank. Some other BMWs have two.

I used Peak Blue DEF Platinum, FWIW. Got it at WalMart.

 

[Bailes1992]

I use around a litre/quart of DEF every 1000miles in my Duster so I think your usage seems very low.

Most of my driving is at 60mph @ 2000rpm with cruise control on.

However, obviously being in the UK our emissions standards are different.

 

[Highlander 1459]

I would guess that it's larger than 2.5gals cause only using 2.5 gal per 20k miles would be abnormally low DEF consumption.

One thing to note, I would expect BMW diesel's to use less DEF than other diesel vehicle since it also uses a LNT (Lean NOx trap), which help reduce NOx, i.e. DEF consumption. According to the EPA benchmarking data on a 2015 BMW N57, the LNT was able to reduce engine out NOx pretty significantly at lower engine speed and load, as you can see below. So if your driving your car in an area of the engine map where the LNT is very effective at reducing NOx, it can probably reduce your DEF consumption by a decent bit compared to other diesel engines.
View attachment 229733

tellya what.. when my Ram 3500 still had a operative DEF system, it had a 5.5 gallon DEF tank and I drove it 11000 miles ( lightly loaded highway operation) before I finally triggered the ADD DEF YOU DUMMY warning light.. you could extrapolate that into thinking something like a automobile, with a smaller less engine would use less DEF than a 1 ton pickup that gets 17mpg.. DEF is injected into the exhaust system proportionate to NOX emissions.. and lightly loaded operation reduces NOx emissions.

 

[OneLonelyBurrito]

tellya what.. when my Ram 3500 still had a operative DEF system, it had a 5.5 gallon DEF tank and I drove it 11000 miles ( lightly loaded highway operation) before I finally triggered the ADD DEF YOU DUMMY warning light.. you could extrapolate that into thinking something like a automobile, with a smaller less engine would use less DEF than a 1 ton pickup that gets 17mpg.. DEF is injected into the exhaust system proportionate to NOX emissions.. and lightly loaded operation reduces NOx emissions.

I know the amount of DEF injected is proportional for the amount of NOx, in a former role, I was involved in exhaust after-treatment system development. The guidelines for DEF tank sizing is the length of an oil change interval, which is why I would be surprised it only used 2.5 gallons in 20k miles. I was able to find the DEF tank size on a 535d, and its 15L, ~4 gals, which makes more sense for 20k lightly loaded miles.

 

[KrisZ]

I think you’re supposed to top it off every oil change, that is why there is no level check.

 

[wavinwayne]

I think you’re supposed to top it off every oil change, that is why there is no level check.

You're probably right. The manual just suggests letting the BMW dealer do everything, or course, but does give instructions for adding DEF in the "exceptional" case that it needs to be added between service intervals. I've attached screenshots from my owner's manual about adding DEF, for reference.

 

[Highlander 1459]

fellas, I know there are regulations determining DEf tanks size and warning devices and refill intervals..
so I started looking on the internet looking... so if you have good reading comprehension levels and patience the info is in the Federal Register
on 46362 Federal Register / Vol. 79, No. 153 / Friday, August 8, 2014 / Rules and Regulations

https://www.govinfo.gov/content/pkg/FR-2014-08-08/pdf/2014-18738.pdf

 

[OneLonelyBurrito]

Looks like BMW sized it to last about 2 service intervals, not 1. So its all starting to come together now.