How do you tell how many gallons in your DEF fluid tank?

I can't find anything. I would suggest one of two things. Call Mercedes-Benz and they may have something on file and then come back and tell us how to find out. Option two is to get a Def filler spout which is designed to prevent you from overfilling or spilling it. I wish you the best of luck.

Almost forgot you can call them at 1-800-FOR-MERCEDES (1-800-367-6372) Press 6 and then press 5. Mercedes-Benz Customer Care Mon-Fri 9am-9pm (EST)

MDClancy- thank you..... Actually, someone at Mercedes Benz told me they think it's the 5.5 gallons....but, my situation is that the light came on and put me in the restart mode ...had to take it to Mercedes Benz to be reset...I challenged them to explain to me WHY the unit when into the reset mode with more than 50 percent DEF fluid left in the tank??? If it really was a 5.5 gallon tank like they said.....?? Now that I'm reading this, it makes more sense that it's a 3.2 gallons tank since it took a little more than two gallons to fill up the tank....I could only believe that it makes more sense that it was really close to the 1 gallon mark when the system tripped the low fluid light? Mercedes said to ignore the owner's manual and keep it filled up every 1,000 to 1,200 miles...I'm going to do this from now on . It's not just mileage, it's idling, hot weather, and other road conditions that eat up DEF..... Only wish there was a fluid gauge for this like the fuel tank.

One more thing....the owner's manual says...once the light comes on you can continue driving for a short distance , then later, it will start the countdown.... didn't do that in my case....it also says, once you add DEF fluid..the system should reset itself in 20 seconds...NONE of this happened.... and put me into the countdown mode immediately.... Bummer...had to take it to the dealership and of course they charged me to restore it back to normal...My advice is don't let the DEF fluid get too low.. System should have reset....

Run it low and see how much it takes to fill it. Keep a bottle in the car in case you run low out on the road.

F_O_R- YES, I'm keeping plenty of DEF on board.... I'll just keep topping it off every 1,000 miles or so.... I'm beginning to think that I really have the smaller tank on the Sprinter.... there's no other logical explanation... When I purchased this vehicle they said I could easily drive 4,000 miles before worrying about it.... NOT TRUE... So, I'll have to check it periodically. Unfortunately, there's no gauge on the vehicle and I even inquired about adding one... they said not possible... Running out and allowing for the warning light to come on is NOT a good idea...The vehicle went into the countdown mode immediately.... Limited engine restarts... Even Mercedes said keep it filled up....it's an inconsistent message between them and the owner's manual... but, I will follow the instructions of the dealership. Other than that, the vehicle is great!!!

How many gallons of diesel fuel does a sprinter whole visit 2016 long wheelbase that too. 14 cylinder engine

I have a 2016 sprinter van long wheelbase 170 inch wheel base with the 2.1. 4 cylinder engine

Mine has the 3.0 BlueTEC. It is a 5.5 gallon. I was remote, and had to drive 75 miles with the light on before I had access to DEF. I added two 2 and 1/2 gallon boxes with no slow down.

For future reference, I go about 8,000 miles on DEF fill up before being asked to add more.

The sensors and DEF system is problematic, I had a countdown on my 2014 and even after adding DEF it kept counting down, on the last start I had to take time off work and drive my van to a sprinter repair shop more than once who reset it once then replaced the sensor, this DEF system is Horrible and this is why people prefer the older sprinters, There are a few Russian techs out there who can bypass the DEF in the ECM and turn it off for around $500. Then you supposedly will get a few miles per gallon better mpg a bit more power and a lot more reliability ..I think I need to do this untill they get this DEF system improved or find a better system as I can't be Having unexpected downtime ...

What brand of DEF are people using in their Sprinters? I have a 2019 REVEL (144, 4WD) and have used the AD BLUE and the Peak Blue DEF. So far they seem to work well. https://www.amazon.com/Diesel-Emissions-Fluid-gallons-2010-2013/dp/B00CGOLZ2A https://www.amazon.com/dp/B07CB25KWM/

From the manual, to be aware of: If the DEF level has dropped below the reserve range, ****add at least 2.0 US gal***** (7.6 l) of DEF at the latest after receiving the second warning message (> page 182). * If you switch off the engine at a low outside temperature and add DEF, restart the engine after refueling. If you leave the vehicle parked without restarting the engine and the DEF freezes in the DEF tank, the onboard computer will only be able to register the new fill level after a defrosting period of up to 60 minutes. During this time the engine may only be operated in neutral.

maclaren65: The brand doesn't matter as long as it complies with ISO 22241. (M-B manual)

Lack of info from a Mercedes it looks like , dealers don’t have a clue and not helpful

I have a 2019 Sprinter Van/Thor motorhome. I have steering wheel controls for the computer. There is a setting in the computer menu that reads the DEF level. The warning messages for low DEF comes on when it hits 1/4 full. I use a 2.5 gal container of DEF when the warning light comes on. This fills the DEF back up to 3/4 full. I have closely monitored the DEF usage for 14,000 miles. I get 1000 miles for 1 gallon of DEF on average. I had the countdown for starting occur once after starting the engine (before refilling the DEF) after the first low DEF warning. When I refilled the DEF, the warning came on the next two starts before resetting back to normal.