Diesel/DEF mileage.

[ddruker]

We get about 1,500 miles per gallon of DEF in our Mercedes GL 350. I fill the DEF tank every 10,000 miles and flush it every 20,000 per the factory service guide - which seems dumb but I am not about to screw with my warranty. Cost is negligible.

In terms of fuel economy, we average about 26 highway, 22 overall and 15 when towing.

[TSchleff]

That is nice to know about the ML350.

Maybe the reason for flushing is that the DEF does have a shelf life.

[RickDavis]

Originally Posted by RickDavis

I have only added DEF to my 2013 Dodge once. Assuming it was delivered with a full tank I used 3.44 gallons in 2100 miles at a cost $9.44 at the pilot pump ($2.79 gal)
That works out to about half a cent a mile. Less if I didn't start with a full tank.
Fairly insignificant in the scheme of things

Just to update my own post, apparently the truck was not delivered with a full def tank.
Not knowing how much would be used I bought a 2.5 gallon jug of the stuff to carry. I have been hauling it around since September when I had filled the DEF tank. As of today I was at the 2500 mile mark so I decided to use the jug before it died of old age.
I was not able to use it all so the DEF mileage is over 1000 mpg.
In addition I notice the stuff is for sale about everywhere now so there is probably no need to carry any of it around.
Almost all my driving has been towing about 5000 lbs.
At this point it appears the cost is insignificant and the availability is good.
If the delivery system proves reliable over the long term the use of DEF should not be a big deal.

I am also happy with the fuel mileage which is running around 15.5 (hand calc.) overall mostly towing for the last 1400 miles. This appears to be only slightly less than my 99 which was not a 4x4 and was 1500 lbs lighter

[TerraYacht]

My colleuague took delivery of his Grand Cherokee a few months ago, and had a DEF fluid warning mere weeks later. The dealer was surprised too, and they determined that Jeep does not fill the DEF tank at the factory, that is supposed to be a dealer prep item. But the dealer didn't know it with his early diesel deliveries.

MY BMW X5 had a full DEF tank, I think, and may have been topped up when it had its warranty-covered oil change: they don't show everything on my paperwork so I will have to ask them at my next visit.

My airstream is self-powered by gasoline, so the 75 gallon tank helps.

[BAB]

I have a '14 Ram 2500 Laramie 4x4 with the 6.7l Cummins. Just turned 6,000 miles on the ODO, of that all but a couple of hundred are tow miles. The DEF gauge showed "Full" when I took delivery, but being the curious sort.....I had a couple of jugs that I'd gotten at Wally's, and it took another gallon (tank is supposed to hold 9). Since it was completely full when I started towing, my calculation based on a refill is "it ain't worth worrying about." The truck is so awesome -- does everything I expected and much better -- that I really am not much concerned about it. Oh, I did add a 37 gal. aux tank in the trunk bed. I can go a LONG way with 73 gallons of diesel...

[jmcarter]

Odd, I've been wondering about the meager DEF usage on my GL350. 18K miles (I deferred DEF service at the 10K service) and I've added one measly gallon and have never gotten a warning. Almost afraid to mention it at my service B next week, afraid they will "fix" it. If anyone knows how the GL's usage could be so minuscule please advise.

[dznf0g]

DEF usage is a function of fuel usage, not miles. Although most of us drive pretty much the same kind of routine (low idle times...etc.) to compare miles per gallon of DEF isn't necessarily accurate. For example a diesel that gets 25 mpg of fuel consumption will use less DEF per mile than a diesel that gets 18 mpg of fuel usage.

[Joe Palmieri]

I have a 2013 GMC 2500 HD Duramax/Alison. The dealer told me they topped off the tank when I took delivery, BS. At 800 miles I dumped 5 gallons into the tank to fill it. I filled it again at 2800 miles and it took 5 quarts. 2.5 quarts per 1000 miles.

[Jim A]

I’ve got a 2012 GMC 2500 HD Duramax/Alison with a shade over 25K miles on it. 95% of the miles have been pulling one of two trailers (FB 27 FC and a 17ft Casita). My best guess is that it seems to get close to the advertised 5K miles per DEF take full. I say, best guess since initially, before trips when the tank mileage was in the 3-4K ish range I’d refill the tank. I never let the DEF level get low enough for the warning message. Then on a trip about as far from a dealer as you can get, the engine/ emission warning light came on and a bit after that, the warning that in 170 miles speed would be reduced (I was 140 miles from the nearest GM dealer). Turned out the emission sensor (don’t remember the exact name) had failed and needed to be replaced. No big deal under warranty but a major cost if out of warranty. First question the dealer asked me after they ran the diagnostic tests and confirmed it was indeed a faulty sensor, was did I refill the tank before for low fluid warning message. Said yes, reply – that’s your problem. Should not refill until the message for low fluid comes on. When we got back home it was time for servicing so I took it into my local dealer. Told them about my problem and again their first question was had I refilled the DEF tank early. Again the response was don’t do that! That was probably the cause of your failure. I was told there was even a service bulletin out telling dealers not to refill the DEF tank before the warning message comes on. Now, I have no idea why refilling early would cause a sensor failure but at this point I’ll wait until the warning comes on. And carry a supply of DEF fluid with me.