DEF shelf life

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

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.

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 Does anyone know what happens if you use "outdated" DEF??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

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

bluwtr49 wrote:
If stored at moderate temps...it should be good for well over a year. After all it's nothing but water and urea (fertilizer)

DEF

Yes, it is just water and urea, and indeed it should last a year at moderate temperatures and out of the sunlight.

At the same time, it does degrade over time. But it is pretty darn cheap stuff, even at the highly inflated prices we might have to pay at some retail establishments.

I note that BMW dealers are supposed to flush and refill diesel car DEF tanks with every oil change to insure that no BMW owner is brought to grief by $10 worth of the stuff. (The DEF tank in my X5 35d holds about 6 gallons. So assuming the tank is relatively full, which it shouldn't be by the time oil change interval rolls around, $10 or so isn't an issue for anybody.)

I don't think the OP has a lot to worry about, unless, of course, he doesn't use up that tank full of DEF over the following summer. In which case, it might not be a bad idea to do a dump and refill each spring just to make sure.

If stored at moderate temps...it should be good for well over a year. After all it's nothing but water and urea (fertilizer)

DEF

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.

According to ISO 22241-3 If stored between 10F and 90F and not subjected to direct sunlight the life expectancy of DEF is a minimum of one year.