I just bought 2 jugs DEF couple days ago and left them behind my drivers seat inside the truck . We have had a couple brutal heat days out here since last weekend ( 110-111 degrees) . I’m thinking the DEF is fine to use but wanted to ask. I guess it’s no different than the DEF sitting in the tank already !?!

 

Ya it's no different than sitting in the tank.

 

Well, I wouldn't say it is the same, sitting in the cab as sitting in the DEF tank.
In cab temps will go considerably higher than outside temps, that's how they bake chocolate chip cookies up on the dash using only the temp generated in the vehicle interior.
But, a few days of sitting in a hot truck cab isn't going to have any noticeable effect on DEF potency, would take months of such exposure to degrade the DEF significantly.
Takes two years of sitting in a warehouse to degrade DEF.
And, even if the DEF starts to degrade, the truck PCM will add more DEF injection to compensate, at least up to a certain point.

 

I'd be more interested in what, if anything, happens to it in the teens (or less) temps.
I keep my 250 in a un heated pole barn, on a 3 amp tender.

Does the DEF heater keep the DEF "usable", when truck is just sitting
which mine does for long stretches, especially in winter).

I've also avoided keeping a jug in the bed for an if/when scenario (just plain forgot to add, and
it's super low away from home), for this reason.

 

DEF will freeze, in a perfect world at 12°F. Below that it'll freeze and the heater in the tank will need to melt it. I don't know how they're getting around that with programming, as there are a great many trucks that use DEF in the great white north that will have that issue all winter...perhaps when the temp is too low it doesn't inject it? I'm not really sure. I do know the DEF heater only functions when the ignition is ON, so if your unheated pole barn gets below 12° for long stretches, then yes, your DEF is freezing.

 

My SD stays in an unheated barn. Temps get to the single digits occasionally. No issues here. DEF also sits in it during the hot summers and the barn can get well over 100

 

DEF isn’t anything special, it’s water and nitrogen.


.

 

This has shelf life guidance that was provided to Ford dealerships in the past.
https://www.google.com/url?sa=t&sour...d88VEMH2QrkGRg

 

Plus it gets transported to stores in semi trailers which im sure reach the same interior temps as your cab.

 

Hi, thanks for this. I was wondering about the DEF in my F350's tank. The temp as been below freezing, but not below -20f for the last week. But after reading the letter from Motorcraft I am not concerned.

Also, I didn't know there was a heater in the DEF tank.

 

As winter approaches I make sure my DEF tank is not overfilled (or even full) so there is no possibility of it freezing and breaking. I almost always buy DEF at truck stop pumps where it might be possible to overfill it. If I fill from a container, I use the Ford nozzle which is supposed to prevent overfilling. Probably just being over cautious.