Everything about Diesel is new to us. We now understand that the rather large looking tank located next to entrance door in lower compartment holds DEF. Part of the Maintenance prior to buying this Coach was to fix engine check lite codes 106200. It states lower limit value of long term adaption of scr system was dropped below. Test DEF fluid - passed- removed EDF injector and clean. also previous code for fuel rail pressure caused by fuel filter. Fuel Filter changed. The tank has obviously been painted high gloss black which I am assuming is for ascetic value and not a rust problem(?) and white "stuff is bubbling up and dripping a bit from the cap. I believe DEF does turn white? Just wondering if perhaps this can become an Issue? Also am curious about the amount of DEF and the weight. I would assume one has to add that figure when determining over all load capacity just like holding tanks, fresh water. The Dealer records appear to be from a reputable Mercedes Establishment and look complete. I have no reason to question the veracity its just that I don't understand mechanical issues and am totally clueless on Diesel Engines. So in simple terms please. and Thanks

Your DEF tank is plastic - no matter what color it looks. DEF is clear but if you let it dry out, you will get a ton of white crystals (which are urea). Check your documentation but DEF tank volumes are 6 to 12 gallons. You can use the weight of water (8 lbs/gal) if you are concerned about weight. I would not worry about weight - you don't worry about the weight of 13 qts of oil in the engine do you? A full tank with the V^ diesel is good for 6-8000 miles so keep a jug and top it off before a long trip.Since you are unfamiliar with diesels, here goes:1. Diesels ignite the fuel air mixture with compression. They do use fuel injection to inject fuel at the precise time to ignite it. Fuel filters need to be kept clean and fuel quality is very important.2. Like all internal combustion engines, diesels have pollution control systems. Similar to cars but very specific to diesels. First up is the DPF or diesel particulate filter. This catches the soot produced by combustion (diesel fuel is not as highly refined as gasoline) which is a major component of air pollution generated by diesels. The DPF is monitored by the engine computer and when it is dirty enough, it is regenerated by burning a big load of diesel fuel in it.3. The second major pollutant of diesel engines is NOx or nitrogen oxides. Two systems are used to control this - the EGR exhaust gas recirculation valve, and SCR or selective catalytic converter. The SCR is the component that uses DEF (diesel exhaust fluid) to react the exhaust with a special catalyst that converts NOx to nitrogen and water.Diesels don't require much maintenance - clean fuel, clean air filters, oil changes once every 15,000 miles or so, DEF, other than those few things, enjoy driving it. One other thing - do not idle it for long periods of time. It won't warm up and you will plug up your DPF.

wow thanks! does that mean that the white crystals "weeping" from the tank lid are bad? or of concern? someone let it dry out?

rv4jimnme - you do not want those crystals hanging around. Basically, the crystals are corrosive. You should was the area down with water and make sure all the crystals are gone, otherwise you are going to have a real issue later on. Statement on the DEF bottle says to remove any spilled or overage of liquid.

well I just bought this from a dealer and the tank was recently painted very shiny do you think this was a problem before? or just maybe the cap is loose. thanks so much for your helpMarlene

Welcome Marlene...LuvLabs has given good advice. I'd add a couple points. DEF fluid is DEF fluid. It all meets ISO 22241 standard. A Crows opine, is that you want to keep the cap and fill port surgically clean to avoid the "white creep". Same with the fill bottle...kitchen counter clean. If you use a funnel, get one only for DEF. Keep it clean and in a zip lock bag. DEF evaporates leaving that creepy white crystal film on everything. That may not be healthy for your DEF system if if it gets inside the tank. Opinions vary as to filling the tank. Some say use the "school solution" and wait for the Lo DEF light. Others favor refilling from time to time. This latter group seems to be growing. I'm in the latter group. Just as crystals form on the outside of the neck and cap, I think it will do the same on inside parts of the tank when they are not wetted and "dry" out. So better to top it off from time to time to keep everything wet. Especially since it is an RV and not driven regularly.

DEF Tank SCR 2011 Fleetwood Tioga Ranger 24L MB Sprinter

12 Replies

rv4jimnme
Explorer
Apr 25, 2017
wow thanks! does that mean that the white crystals "weeping" from the tank lid are bad? or of concern? someone let it dry out?
luvlabs
Explorer
Apr 24, 2017
Your DEF tank is plastic - no matter what color it looks. DEF is clear but if you let it dry out, you will get a ton of white crystals (which are urea). Check your documentation but DEF tank volumes are 6 to 12 gallons. You can use the weight of water (8 lbs/gal) if you are concerned about weight. I would not worry about weight - you don't worry about the weight of 13 qts of oil in the engine do you? A full tank with the V^ diesel is good for 6-8000 miles so keep a jug and top it off before a long trip.

Since you are unfamiliar with diesels, here goes:
1. Diesels ignite the fuel air mixture with compression. They do use fuel injection to inject fuel at the precise time to ignite it. Fuel filters need to be kept clean and fuel quality is very important.

2. Like all internal combustion engines, diesels have pollution control systems. Similar to cars but very specific to diesels. First up is the DPF or diesel particulate filter. This catches the soot produced by combustion (diesel fuel is not as highly refined as gasoline) which is a major component of air pollution generated by diesels. The DPF is monitored by the engine computer and when it is dirty enough, it is regenerated by burning a big load of diesel fuel in it.

3. The second major pollutant of diesel engines is NOx or nitrogen oxides. Two systems are used to control this - the EGR exhaust gas recirculation valve, and SCR or selective catalytic converter. The SCR is the component that uses DEF (diesel exhaust fluid) to react the exhaust with a special catalyst that converts NOx to nitrogen and water.

Diesels don't require much maintenance - clean fuel, clean air filters, oil changes once every 15,000 miles or so, DEF, other than those few things, enjoy driving it. One other thing - do not idle it for long periods of time. It won't warm up and you will plug up your DPF.

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DEF Tank SCR 2011 Fleetwood Tioga Ranger 24L MB Sprinter

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