DEF tank

DEF usage is much smaller/slower than the diesel fuel itself. Do NOT put any DEF in with the diesel. If you run low you should be getting a warning , will be slowed down in limp mode and if you keep going eventually the engine could shut down to protect itself. As stated earlier, you can buy DEF at most truck stops in containers or via a pump in the truck area. Walmart sells in 2.5 and 1 gallon jugs. 2.5 gallons is just under $11.00 so yes, is cheaper from a DEF pump at a fuel stop.

Please read your manual. I am also fairly new to diesel and I had and still have lots to learn. Very different animal than gas......... Read about proper starting, cooling down and additives that may or may not be recommended for your unit. Your manual gets you the best answers for your system. Happy RVing!

The OP's DEF filler is under the hood as the Navion chassis is a Mercedes Benz Sprinter. Why all the speculation and off topic discussion?

C-Bears wrote:
I guess everyone is entitled to their own opinions. Obviously the Utube video shows some folks may put the wrong fluids in the wrong hole in their diesel trucks or RV's.

I just know as an owner of a diesel truck that uses DEF, I need a step stool to even check my oil. Being 6'1" tall I sure don't want Ford to locate my DEF filler under the hood so I have to pull out a step stool or step ladder to fill the darn thing when I'm in the truck lanes at a Pilot station. Trucker's would get a real kick out of that!

If Ford would locate it under the hood then there would probably be some idiot that would dump oil in it, or put DEF in their oil fill for that matter.

Unless you actually drive and/or tow with a diesel that uses DEF then you probably should not be locked into an opinion on where the DEF fill should be located. If Ford ever decides to put the fill under the hood then I have purchased my last Ford.

My wife's about 5'10" and she can fill our 2500 Duramax under the hood with no problem.

I guess everyone is entitled to their own opinions. Obviously the Utube video shows some folks may put the wrong fluids in the wrong hole in their diesel trucks or RV's.

I just know as an owner of a diesel truck that uses DEF, I need a step stool to even check my oil. Being 6'1" tall I sure don't want Ford to locate my DEF filler under the hood so I have to pull out a step stool or step ladder to fill the darn thing when I'm in the truck lanes at a Pilot station. Trucker's would get a real kick out of that!

If Ford would locate it under the hood then there would probably be some idiot that would dump oil in it, or put DEF in their oil fill for that matter.

Unless you actually drive and/or tow with a diesel that uses DEF then you probably should not be locked into an opinion on where the DEF fill should be located. If Ford ever decides to put the fill under the hood then I have purchased my last Ford.

C-Bears wrote:
I have read about folks putting gas in a diesel tank, and/or diesel in a gas tank. Usually hear about it on forums from someone that heard about it from someone else that heard about it.....

I know people read stuff and immediately believe it, but based on my limited experience (someone that actually has a truck which uses DEF) I think it would be impossible to put a diesel nozzle, which even the small ones measure about 1 3/4" wide, into a DEF inlet which are about 7/8" wide. I mean come on, when that big thing won't go into that little thing, no one that is sober is going to just pull the trigger and start shooting diesel toward the DEF opening!

DEF in diesel is bigger issue and happens.....

Diesel Mechanic

I have read about folks putting gas in a diesel tank, and/or diesel in a gas tank. Usually hear about it on forums from someone that heard about it from someone else that heard about it.....

I know people read stuff and immediately believe it, but based on my limited experience (someone that actually has a truck which uses DEF) I think it would be impossible to put a diesel nozzle, which even the small ones measure about 1 3/4" wide, into a DEF inlet which are about 7/8" wide. I mean come on, when that big thing won't go into that little thing, no one that is sober is going to just pull the trigger and start shooting diesel toward the DEF opening!

And just a quick note for those that don't think it can happen...at least not to them.


Many folks have put diesel in gas tank, gas in diesel tank and DEF in diesel tank.

Why folks have even brushed their teeth with Prep H, used baking soda vs baking powder etc.
Thing is people make mistakes.....you can't dummy proof everything.

May you never have that :S :S :S moment and continue with your unblemished life

IND_navyvet wrote:

dcmac214 wrote:
Question out of idle curiosity (DEF not something I have to worry about).
What happens if you run out of DEF and don't refill?

Creep mode, 5mph. After that no idea, but probably no go.

yep, limp mode....but you're given a warning and a distance you can travel before you would go into limp mode....no big deal...you can get 2.5 gallon Blue Def at Wally World and a whole lot of other places now a day's...can also get at the pump, (google DEF pump locations). One can purchase a 2.5 gallon of DEF and keep it with them if they think they might need it. In 2 yrs 2 months and 32,000 miles on my truck, I've never come near even getting the low level warning.....I even stopped carrying the 2.5 gallon jug, "just in case"...I get it at the pump about 5 miles from my house. Once I got full time, may start carrying a 2.5 gallon reserve just in case...but it's MUCH cheaper at the pump.

On edit: I had a 2010 non DEF Ram 3500 DRW/CC/LB/Cummins with 68RFE and 4.10, in Laramie trim, then a 2012 Ram DRW/CC/LB/Cummins with 68RFE, 4.10/HO in Longhorn trim, neither with DEF....I now have truck in my sig..it's heavier with new front and rear suspension, frame and Aisin is heavier than 68RFE, BUT with DEF I get better MPG towing and empty than I did in my 10' or 12' without DEF.......DEF is a plus, cost per mile is miniscule.

dcmac214 wrote:
Question out of idle curiosity (DEF not something I have to worry about).
What happens if you run out of DEF and don't refill?

Creep mode, 5mph. After that no idea, but probably no go.

Question out of idle curiosity (DEF not something I have to worry about).
What happens if you run out of DEF and don't refill?