Diesel Engine Fluid Tank (DEF) Capacity

[Brian Dyck]

I recently bought a Seneca 36FK. Have researched all the manuals, Cummins, Freightliner, Jayco, and nowhere can I find what the capacity is for the DEF tank. Looking at the tank I am guessing it is somewhere around 5 gallons. Would appreciate knowing how much DEF I should buy to replenish the tank.

[Sundancer330]

The specs for a 2016 is 6 gallons, not sure of other years but probably similar.

[Robbbyr]

Yes, all the Seneca M2's have a 6-gallon Diesel Exhaust Fluid tank.

The new S2RV chassis have a larger tank.

[Mark S]

I find it easier and cheaper to buy DEF at the pump when I fill up at truck stops. I try to refill every 2-3 fill ups. I carry a couple of gallon jugs of DEF for the just in case but so far I have not had to use them.

[Robbbyr]

Originally Posted by Mark S

I find it easier and cheaper to buy DEF at the pump when I fill up at truck stops. I try to refill every 2-3 fill ups. I carry a couple of gallon jugs of DEF for the just in case but so far I have not had to use them.

Don't keep your extra DEF too long before you use it, it can degrade over time. Especially if stored somewhere that gets hot.

Sunlight also can cause it to deteriorate, but it isn't likely you have it stored on the roof!

[jkaras7]

Originally Posted by Robbbyr

Don't keep your extra DEF too long before you use it, it can degrade over time. Especially if stored somewhere that gets hot.

Sunlight also can cause it to deteriorate, but it isn't likely you have it stored on the roof!

Thanks for that info. Did not know that DEF deteriorated.

[Mountain Cajun]

I tried to get an exact amount on my DEF tank my last trip. I think the gauge is just as bad as the diesel tank. I read it is a six gallon tank. I had 2 1/2 gallon just ready to use if I ran out. The last light turns yellow and can’t get but 4 gallons in. So I ran it till the yellow light finally turned red and flashing. I went 40 miles like this and got to my required fuel stop and still only put 4 1/2 gallons in! ????


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[Robbbyr]

Long-term storage above 90 Fahrenheit; below freezing; and exposure to sunlight can cause it to deteriorate. That heat thing might be a factor in Las Vegas!

I keep a 2.5 gallon "box" with me too, but I make sure I use it within a couple of months. No telling how it was transported/stored before I bought it! Filling it at the Pilot/Flying J pumps sure is convenient on the road.

[Crossingover]

DEF is 67% water and 33% urea. Consider the date code on the DEF container when factoring how long to keep it before use.

From a November 2014 Ford dealer bulletin:

DEF Shelf Life versus Temperature
Constant Ambient Storage

Temperature Shelf Life (Months)
≤50 °F (10°C) 36
<77 °F (25°C) 18
≤86 °F (30°C) 12
≤95 °F (35°C) 6
<104°F (40°C) 2

[Tumbleweed44]

That's good info to know.
I am a truck driver and asked one of our mechanics about DEF life. Specifically, how does freezing affect the DEF. His answer was "There is a heater in the DEF tank. Once the DEF thaws out it's fine. Freezing does no damage".
I was concerned about that since I have no long trips planned until next March and it's likely to get a bit chilly before then!

[jkaras7]

Originally Posted by Crossingover

DEF is 67% water and 33% urea. Consider the date code on the DEF container when factoring how long to keep it before use.

From a November 2014 Ford dealer bulletin:

DEF Shelf Life versus Temperature
Constant Ambient Storage

Temperature Shelf Life (Months)
≤50 °F (10°C) 36
<77 °F (25°C) 18
≤86 °F (30°C) 12
≤95 °F (35°C) 6
<104°F (40°C) 2

Great info. Thank you for taking the time to post this.

[Mark S]

Does anybody else find it odd that synthetic pig urine would have an expiration date?

I just added a gallon from a 1 gallon container of DEF for the first time. What a PIA. The vent leaks and it takes too long. I will be getting all my DEF from the pump like I've been doing.

Ps- John and Marcie----I'll be out in Vegas over Thanksgiving visiting kids and grandkids who live in Mountain's Edge. Not camping tho, staying in Cancun Resort.

[rgolding]

Originally Posted by Mountain Cajun

I tried to get an exact amount on my DEF tank my last trip. I think the gauge is just as bad as the diesel tank. I read it is a six gallon tank. I had 2 1/2 gallon just ready to use if I ran out. The last light turns yellow and can’t get but 4 gallons in. So I ran it till the yellow light finally turned red and flashing. I went 40 miles like this and got to my required fuel stop and still only put 4 1/2 gallons in! ????


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So Buddy Brown,

Do you like anxiety? I appreciate your test efforts and will use the knowledge you obtained, but Holy Cow you must enjoy paper cuts and sleeping in Poison Ivy. Thanks for documenting your tests, I really mean that. I've just always fill when the second light goes out and before the third one goes out. Usually put in under 3 gallons.

[Mountain Cajun]

Ha Ric! I just like things to work like they are supposed to. Seems in the RV industry they attempt to but that’s not the case. (If your not living on the edge, your taking up space!) [emoji13]


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[Brian Dyck]

Another newbie question. Manuals recommend using Fleetguard brand DEF. Is it far superior to other brands or simply more expensive? Anybody experienced any problems with using other brands?

[Crossingover]

Originally Posted by Brian Dyck

Another newbie question. Manuals recommend using Fleetguard brand DEF. Is it far superior to other brands or simply more expensive? Anybody experienced any problems with using other brands?

Just a standard recommendation, just like using Fleetguard filters and whatnot. It's more important to use fresh DEF. I get all mine at the truck stop pump.

[Robbbyr]

Originally Posted by Crossingover

Just a standard recommendation, just like using Fleetguard filters and whatnot. It's more important to use fresh DEF.

X2
I use the truck lane DEF pump when traveling longer distances, Peak Blue DEF in a box when the adventures are closer to home. Never had any issues.

[rgolding]

We almost always top off the DEF at a Love's truck stop. Have never had a concern. Like others have stated, lots of recommendations are just disclaimers.

[RichP]

Originally Posted by Brian Dyck

Another newbie question. Manuals recommend using Fleetguard brand DEF. Is it far superior to other brands or simply more expensive? Anybody experienced any problems with using other brands?

fleetguard is owned by cummins, so they are just encouraging you to use the oem equipment. just like ford pushes motorcraft. Not that one is better than the other, but that is what it was designed to work with. DEF is simple stuff as long as it has the api certification you should be good to go