ddruker

There have been a bunch of postings on the high cost of ADBlue, aka Diesel Exhaust Fluid (DEF), aka ISO 22241 AUS32 (Aqueous Urea Solution 32.5%) for the GL 350. I've found the opposite to be true - it's so cheap it's irrelevant. Here's the math.

In my first 5,000 miles, I've consumed almost exactly 2.5 gallons of DEF. I know since once a month I top off my ADBlue tank, and I just finished off my first 2.5 gallon jug of DEF.

I spent $13 on the 2.5 gallon jug - that works out about 25 cents of DEF for every 100 hundred miles driven... In terms of fuel consumption, I'm averaging roughly 25 MPG so far over my first 5k miles.

Filling your AdBlue tank yourself is about as hard as filling your windshield washer fluid, and DEF is now widely available in auto parts stores. Just keep the area clean when you are filling the tank.

Are others seeing similar results and consumption levels?

aeggroup

MB recommends to add ADBlue once a year or every 10K miles.
May I ask you - why do you add it once a month ? Is there any benefit of doing so ?

Thanks.

ddruker

I like to spend about 30 minutes a month doing routine maintenance, that's all. I check and top off fluids, make sure the tires are inflated, look for places I need to do some extra cleaning, etc.

I have heard others say it's a good idea to keep the DEF tank topped off - less air in the tank means less evaporation.

I'm not sure why Mercedes recommends flushing the DEF tank at 20k miles - it could be they are worried about said evaporation causing crystallization in the tank, or it could be they think DEF has a limited lifetime.

Anyway, I can't think of any harm in keeping it topped off.

Fourdiesel

Evaporation in a closed tank (air vent only) is a non issue. No measurable change in concentration is possible. Cleaning the outside where powdery residue from splashes and drips from the container may build up - that's logical but I see no benefit from a flush of the system. The 30% concentration is no where near the precipitation point of the mixture so crystals of solid urea cannot build up in the liquid. I can think of no reason to flush except to make the dealer rich - and to make jobs for the techs and the service writer.

listerone

Everything I've read (including the bottle of DEF that I bought at a VW dealership) clearly indicates that DEF has a finite shelf life...that is,over time natural chemical processes cause it to break down and become something else,chemically speaking (God only knows what ).So keeping the tank topped off almost certainly isn't a good idea it would seem...although I *did* flunk chemistry in school .And flushing the tank periodically is probably meant to remove potentially problematic (having changed chemical characteristics) droplets/particles that might otherwise adhere to the tank walls.

And FYI...BMW also recommends periodic flushing of the DEF tank (either annually of bi-annually,can't recall which).

listerone

About $13 for a 2.5 gallon jug was what a local VW dealership was charging a year or so ago when I inquired.Both my diesels (small/medium sized sedans) hold/held about 6 gallons of DEF and are both said to go about 10K miles on those 6 gallons.I see DEF as being nothing more than a minor inconvenience and a minor expense.....so far,at least.

mp0i

I subscribe to the flush it out every two years plan. I buy the DEF at Pepboys at about $17/2.5 gallons and give it to the dealer and have him take care of it. I don't mind paying for the labor but avoid being taken advantage of on the cost of DEF by the dealer. This way there is no warranty issues with having the maintenance performed. I have already done my ML this way and will most likely do the GL in a few months.

Fourdiesel

The attached shows the 32.5% urea solution is completely stable between the temperatures of +12.5 F and +122F. It will not break down. If it does reach 122F it will slowly release ammonia (which has a strong odor) and CO2. That's what it MIGHT change to. It is neither an issue nor a problem if that happens. Actually, if you top off more frequently, you stand a better chance of smelling breakdown products. But ammonia dissolved in the liquid will not change the way the stuff reacts in the exhaust of your car. I fact that is what it is supposed to do - turn to ammonia in the exhaust so the ammonia can change the NO2 to N2 and water at the ceramic SCR interface.

mp0i

Fourdiesel--Good article on adblue.

So... what happens if you do not flush the adblue tank at the Service B (20,000 miles) and an issue comes up with the emission control system? Will M-B fix the problem or will they say "well you didn't flush the tank so we are voiding the warranty". Any thoughts?

Fourdiesel

Throw enough conditions at a hypothetical and an impossible situation is created (or you are pushing for a particular answer). First, I've heard of no issues concerning the SCR (urea) converter plugging up. Thus it is unlikely. Second, so much depends on the personal relationship the owner has with the dealership involved. I know of one service writer at the dealer I usually go to that I KNOW would turn down any request I might make - on the other hand, the advisor I usually talk to is very cooperative and respects my input. If that were not so, I'd be going elsewhere!
Thus, even if the 'emissions' part was failing, I'd expect them to cover it (within the emissions warranty of course) even if I hadn't flushed the AdBlue system.

mikapen

I kept waiting for my AdBlue dash lights to come on so I could see what they look like, but at 12,500 miles I gave up and filled the AdBlue tank.

I bought the AdBlue at NAPA where it was $9.99 per 2 1/2 gallons. I let the dealer fill the tank and do some sort of reset (I guess you have to tell the computer that you added - maybe because of the "flush") and they didn't charge labor. Part of a larger service.

I used @ 6.0 gal of AdBlue for the 12,500 miles. I am getting about 26 mpg overall on my 2010 ML.

43221B

There is no reset on the GL after filling the adblue tank. The service advisors like to tell you there is though.