Since the def can go bad, what does bad def do? I bought a def checker to be sure mine was ok, not to old, not to hot, not to cold ,etc.Since it only added to the exhaust?? why do we have to be worried about the def being spoiled?

 

it does have a shelf life that is directly linked to ambient temperature. at 40*C its 3 months...0*C the shelf life is infinite.

urea freezes at 11*C and this is normal and will not damage it. The concern i have is expansion in the def tank if it is filled full. I do not know if there is adequate head space in the tank to account for freezing expansion. I have seen a lot of def pumps replaced but do not know if that is an attributing factor.

most new trucks have a quality sensor.

the weaker def fluid becomes, the less effective it is as a reductant; chemically reducing NO2 AND NO3 TO N AND 02. There is an adaptive limit to the system so if the urea gets to dilute the system can't compensate for it.

the other issue is hydrocarbon contamination...if any fuel gets into the def system it destroys the def tank heater element. never fill the fuel tank with the def cap off. never fill both at the same time.