DEF shelf life

[eheading]

I have read that DEF has a definite shelf life, and I've heard figures of around 6 months. Given that most of us don't use our motorhomes in the winter, or at least like in my case, only on relatively short distances, the DEF in my motorhome tank is going to be over 6 months old by spring.

My question is - what happens when it "deteriorates"? Does it mess up the system, or just not work as well??

Ed Headington
2013 Ventana LE

[Mr_Mark1]

Holstein, I also wonder how accurate the built-in fuel mileage computer will compare to my pencil to paper calculations. I'm also writing down the mileage and fuel added at every stop.

One long 780 mile traveling segment (2 days) through Texas with a 15-20 mph headwind going about 70 (wanted to stretch the Elegant Ladies legs), we were averaging 5.8 mpg. Our toad weighs 3,500 lbs. I feel that once the engine is broken in, our total average over time will be between 6.5-6.8.

I'll keep an eye on the DEF usage. Since I only filled it once, I'm not sure how accurate the needle is and if it was filled to the brim when I picked the coach up. We started off with almost 3,200 miles at delivery and now have about 6,800. The coach had to be driven from Canada (bus shell) to the converter (N. Chicago) then to the painter (in Indiana), back to N. Chicago, then to Stuart, FL, for delivery. All the fluids were changed and the chassis serviced before delivery.

Prevost said I can go 35,000 miles between oil changes or once a year. I stopped in Ft. Worth Texas at the Prevost service center to have a defective fog light replaced under warranty (the reflective material inside the bezel was discolored).

Safe travels,
MM.

[mpierce]

Cummins says around 3% DEF vs fuel. Burn 100 gal diesel, burn somewhere near 3 gallons DEF. I was using 8% in my Dodge Cummins pickup. Had it flashed again, with update, and it went down to where it should be. If you are over 4-5%, contact your engine maker, should not be that high.

[holstein13]

Mr.Mark wrote:
Holstein, I'm getting about 6.0-7.2 mpg from what I can tell. If I keep it at 60 vs. 70.... I can get a whole 1 mpg more at almost 7.2 mpg if the terrain is fairly level without strong headwinds.

I know it takes a lot of miles to get a true mpg average. I haven't weighed our coach yet but was assured that we weigh about 54,000 lbs. wet.

MM.

Wow, if you are getting 6.6 MPG, then you are burning DEF at a 4.4% rate. You may wish to get that checked out. That seems excessive. Are you sure it's normal? Everything I read says 2-3% with 3% being closer to average.

I'm averaging about 6.2 - 6.4 MPG towing my 6,000 pound toad but I drive around 66 to 68 MPH now. I used to drive slower with my old coach but this one feels safer than my gasser. I've only got 4,700 miles on the coach now so I don't know for sure and my trip computer looks like it was disconnected a week ago when they worked on my dash. Gotta get that fixed now.

I keep detailed fuel records, but with the diesel generator and the diesel furnace, my fuel records don't count for much. I'm getting about 5.8 mpg over all if you only look at the diesel in vs miles.

[Mr_Mark1]

Holstein, I'm getting about 6.0-7.2 mpg from what I can tell. If I keep it at 60 vs. 70.... I can get a whole 1 mpg more at almost 7.2 mpg if the terrain is fairly level without strong headwinds.

I know it takes a lot of miles to get a true mpg average. I haven't weighed our coach yet but was assured that we weigh about 54,000 lbs. wet.

MM.

[holstein13]

Mr.Mark wrote:
We have a 16 gallon DEF tank in our new coach and I just filled it for the first time. We drove 2,300 miles on a little less than 15 gallons.

Mr. Mark, I'm glad to see you are burning as much DEF as I am. If you are getting roughly 6 mpg, then you are at a 3.9% burn rate. I'm about 3% myself.

I was thinking something was wrong with my coach because I've read about others getting 1 - 2%.

[Mr_Mark1]

GoPackGo wrote:

Mr.Mark wrote:
I found this excerpt on a DEF site.

"The shelf life of DEF is two years if the fluid temperature remains between 12°F (-10°C) and 86°F (30°C). Where DEF is stored outside in bulk tanks or totes then heating and cooling solutions are available to ensure it is kept within the correct temperature range. Cooling is usually achieved by insulation and ventilation. Air conditioning is not required."

I don't think the magic time of 6 months is going to make DEF useless. Like my fuel tank, I would fill it up before storage as to keep the air in the tank to a minimum. For us, we'll use the coach on a monthly basis and we will not be in extreme temps cold or hot. With the tanks being inside the bay area, it would take extra extreme temps to change the temp of the DEF.

We have a 16 gallon DEF tank in our new coach and I just filled it for the first time. We drove 2,300 miles on a little less than 15 gallons (don't have the receipt in front of me).

MM.

Mr.Mark - This indicates you got 153 mpg of DEF. Is that about normal for a Class A ? Just wondering. I drive an F350 so I'm not up to speed on Class A DEF consumption.

Tim

Tim, I would think it is normal as that is my first tank. I'll keep the forum posted on future refills.

We have a 230 gallon fuel tank and a 16 gallon DEF tank.

Mark

[bluwtr49]

Old-Biscuit wrote:
Biggest issue with non use is crystallization which clogs up system.

I can not think of any reason DEF would crystallize in a sealed tank. Granted if there is an external leak someplace or if the DEF in a line is exposed to air than the water could evaporate and leave Urea deposits which is a powder. But even then it should go back into solution with the addition of water. I would think that regular use should prevent that completely no matter what the age of the DEF.

[nevadanick]

You can reuse the containers. Like i said about aging def, it will depend on how picky the emmissions system is. Mercedes told me that i could run distilled water in a pinch and get no limp mode, just a check engine light. My GMC would probably go into limp mode on straight water.

[donee]

I have a question regarding the DEF.
Would the reuse of the DEF bottles harm anything or is it OK?
I have two empty from a recent trip and was thinking about\refilling them and keeping them in the basement storage.
Thanks.

[GoPackGo]

Mr.Mark wrote:
I found this excerpt on a DEF site.

"The shelf life of DEF is two years if the fluid temperature remains between 12°F (-10°C) and 86°F (30°C). Where DEF is stored outside in bulk tanks or totes then heating and cooling solutions are available to ensure it is kept within the correct temperature range. Cooling is usually achieved by insulation and ventilation. Air conditioning is not required."

I don't think the magic time of 6 months is going to make DEF useless. Like my fuel tank, I would fill it up before storage as to keep the air in the tank to a minimum. For us, we'll use the coach on a monthly basis and we will not be in extreme temps cold or hot. With the tanks being inside the bay area, it would take extra extreme temps to change the temp of the DEF.

We have a 16 gallon DEF tank in our new coach and I just filled it for the first time. We drove 2,300 miles on a little less than 15 gallons (don't have the receipt in front of me).

MM.

Mr.Mark - This indicates you got 153 mpg of DEF. Is that about normal for a Class A ? Just wondering. I drive an F350 so I'm not up to speed on Class A DEF consumption.

Tim

[Old-Biscuit]

Biggest issue with non use is crystallization which clogs up system.

[bluwtr49]

Apparently the action of DEF relies on thermal decomposition of the the Urea/water at the high operation temperature of the reactor. This sort of reverses the the process that make urea initially which suggests that the low(er) temperature decomposition is very similar merely slower which would explain my the shelf life is longer with lowered temp exposures.

If this is indeed correct than operating with DEF older than the expiration date would probably not have any affect unless it was really old or stored at high(er) temps. Than it probably would just be less effective and take more DEF per cycle.

This is just a guess but Urea is not very complicated so the decomposition byproducts are pretty limited.

[eheading]

Thanks all. That is encouraging. Does anyone know what happens if you use "outdated" DEF?? Does it just not clean up the emissions correctly, or is it more severe?

After I posted the original post, I realized that when we bought our new motorhome in February, it was a left over 2013, and probably the DEF had been sitting in the tank for a year or more, including a summer here in Florida. I never detected any problems with that tank full, so probably it isn't really critical. Your answers have sort of confirmed that.

thanks again,
Ed Headington

[nevadanick]

Some of it depends on how picky the emmissions system is. I personally dont worry about it and just fill when needed.