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Mercedes Sprinter Maintenance: Diesel Emission Fluid (DEF)
Photographer and cyclist and Mac expert and software engineer Lloyd Chambers is available for consulting on general Sprinter considerations at his usual consulting rates via phone, or in person in the Palo Alto, CA area. Save yourself hours and mistakes by discussing issues up-front. More about Lloyd....
BlueDEF® is a mixture of 32.5% high purity synthetic urea and 67.5% deionized water that is used in Selective Catalytic Reduction(SCR) systems on diesel engines.
DEF is the primary ingredient used to help convert NOx to harmless nitrogen and water.
BlueDEF is stable, colorless, non-flammable, non-toxic and is classified as minimum risk for transportation. BlueDEF conforms to the ISO-22241-1 specification for DEF, is API registered and meets or exceeds OEM specifications.
The shelf life of DEF is directly related to the temperature at which it is stored. Storage temperature between 12° and 86° F are recommended to maintain optimal shelf life of up to two years. If BlueDEF freezes, its efficacy will not be effected upon thawing. To maintain the purity of DEF and not harm the SCR Catalyst System care must be taken regarding the material of construction for all items that come in contact with the DEF solution.
Page 126 of the 2017 Mercedes Sprinter user manual states offers some important warnings:
Only use DEF in accordance with ISO 22241. Never mix DEF with additives or thin it with tap water. The exhaust gas after- treatment may otherwise be damaged. Observe the MB Specifications for Service Products, Sheet 352.0. Damage that results from the use of additives or tap water leads to the loss of the New Vehicle Limited Warranty.
If DEF comes into contact with a painted or aluminum surface, wash the surface off immediately with plenty of water.
DEF is not a diesel additive and must not be mixed with fuel in the tank. Even small amounts of DEF can cause engine damage. Damage that results from the blending of DEF will not be covered by the New Vehicle Limited Warranty.
Containers made of aluminum, copper, copper alloys as well as unalloyed or galvanized steel are not suitable for storing DEF. If stored in these types of containers, DEF could cause constituents of these metals to dissolve and cause irreparable damage to the exhaust gas after-treatment. Damage caused by such impurities in the DEF will invalidate the New Vehicle Limited Warranty. Only store DEF in containers made of high-alloy Cr‐Ni steel or Mo‐Cr‐Ni steel in accordance with DIN EN 10 088‐1/2/3 or plastic containers made of polypropylene or polyethylene.
Best advice: use it out of the original container and never anything else and you’re 'good'.
Miles per gallon for DEF fluid
The 3.0L 6-cylinder engine in the 2017 Mercedes Sprinter takes 4.7 gallons of Diesel Emission Fluid (DEF) according to page 277 of the 2017 Mercedes Sprinter user manual.
Shown at right is the DEF level shown in the 2017 Mercedes Sprinter display after driving 1270 miles and starting with a full reservoir of DEF.
In the first 1270 miles, the 2017 Mercedes Sprinter 3.0L 6-cylinder engine consumed at least a gallon of DEF, because refilling the reservoir with a gallon of DEF still left the gauge less than full.
At 4000 miles it became clear that the DEF gauge is inaccurate, at least from the 75% to 100% level—it can be down a gallon and indicate almost full, or be not full and indicate full, etc. The best way to deal with this is to top off the DEF fluid slowly so as not to spill out of the top but yet to fill it fully.
Conservatively, it looks like about 1100 miles per gallon for DEF fluid. However, that initial figured is derived from about 75% driving at very high altitude (over 6000' elevation); operation closer to sea level might consume less DEF.
Unless a very long trip is planned, there is little reason to carry DEF fluid assuming the reservoir is topped off before leaving. DEF fluid is readily available at auto parts stores, Walmart and similar stores or Amazon.
Amazon carries Peak Blue DEF at a good price, particularly with Subscribe N Save:. Prices seem to vary, but at one point I purchased it for as low as $6.74/gallon whereas it the price jumped 2 weeks later to about $11.74/gallon; check around for best prices.
The Lisle 17232 Right Angle Funnel works well for adding DEF fluid.