# DEF Manufacture Date



## BlueTopaz (Aug 25, 2012)

Also purchase from a local truck stop that has it at the pumps. It is always a fresh supply and the tanks are underground where the temp is cooler. Not to mention it is easier to dispense and is lesser in cost. I have noticed more places are getting it installed at the pumps.

You can search here.


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## mkohan (Dec 19, 2015)

*Agreed that DEF at the pump is the way to go. Convenient, cheaper & fresher. I'm using about a gallon of DEF per 3k miles. Every 10k of driving I stop in to fill up.*


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## TX CTD (Oct 24, 2014)

If you need it, pump is the best way by far.


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## BlueTopaz (Aug 25, 2012)

I did score 2 gallons of Blue DEF that was on clearance at Walmart for .50 a gallon. I took a chance and grabbed it. Turns out I was down exactly 2 gallons because that filled my tank. Been over a month now and no issues. Didn't check the date code.


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## boraz (Aug 29, 2013)

youre waaaay overthinking this.

go buy def and use it.

i, and every mechanic ive asked are not aware of one situation where 'bad def' was to blame.


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## MOTO13 (Mar 26, 2014)

What exactly goes bad with DEF which is basically ammonia? I agree buy the freshest possible just because it makes sense. Does old DEF harm the sensors or give false reading to the sensors? DEF never enters the engine, it is simply injected into the exhaust to make a CTD...a CTD.


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## boraz (Aug 29, 2013)

MOTO13 said:


> What exactly goes bad with DEF which is basically ammonia? I agree buy the freshest possible just because it makes sense. Does old DEF harm the sensors or give false reading to the sensors? DEF never enters the engine, it is simply injected into the exhaust to make a CTD...a CTD.


def exposed to air crystallizes, keeping the reservoir less than full adds to crystallization, crystals equal issues, clogs...

the sensors read the differential pre and post def injection, if readings are off, def gets blamed...but its always the sensors gone bad, or not enough/too much being injected


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## MOTO13 (Mar 26, 2014)

See, this is what makes this site, this site. Experts. Thank You.


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## CruzeDan (May 17, 2015)

DEF does expire, and it will cause issues if it is bad. It's unlikely, but possible. Most of it has a date on the bottle, I know the ACDelco does. That's what I use in my car because I am anal retentive


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## bestleonard (Jul 14, 2021)

I still don't know how to read expiration date on ACDelco. 
1) Printed on back label: 042621A
The following code is print on bottom of ACDelco 1-gal, DEF fluid.
00690405211519-4
This longer code does not match the date analysis in the above post.

If anyone knows how to 'de-code' and get mfg. date, please post and let me know.
Thanks,
bestLen


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## BDCCruze (Jul 12, 2017)

I got lucky with this. Early in my CTD life I 'stocked up' and bought like 2 or 3 jugs of DEF that I didn't need. Thankfully I didn't have problems with them since it was over winter and I put a ton of miles on my car so I used it within a year.


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## 15cruzediesel (Sep 30, 2019)

DEF technically doesn't expire or go bad if it is not opened and introduced to atmosphere.

What happens is it loses its water content and that changes its urea to water ratio. Storage should always be in a cool place.

As long as it is clear and not cloudy it will be fine.

Best practice is to keep a clear jug and buy it at a truck stop that has a lot truck traffic as others have said although most probably just buy it at a local store and that works also.

Me I keep my def full not letting it get lower than a gallon with the intent of keeping the heater always submerged. I have a theory these heaters fail when people wait for the def low message to come on. Just a theory and I'll see if my heater goes the distance or gives me the dreaded count down at some point.


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## Snipesy (Dec 7, 2015)

15cruzediesel said:


> DEF technically doesn't expire or go bad if it is not opened and introduced to atmosphere.
> 
> What happens is it loses its water content and that changes its urea to water ratio. Storage should always be in a cool place.
> 
> ...


It breakdowns into ammonia… Which just goes into the solution. This is actually better for SCR.

But it does affect the refractive index which is what the ECM uses to detect bad DEF. It has to be pretty bad for this to happen. Like you let it sit in direct sunlight when it’s 140 degrees.

Needless to say… Stored in a cool dark place…. DEF will outlive you, your kids, and their kids.


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## MP81 (Jul 20, 2015)

I usually buy 2-3 jugs at a time (cut down to two now that we don't drive nearly as much) and store it in my basement, so that should be the optimal place for it (since it sits at like 70 all the time and isn't damp).


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## 15cruzediesel (Sep 30, 2019)

Snipesy said:


> It breakdowns into ammonia… Which just goes into the solution. This is actually better for SCR.
> 
> But it does affect the refractive index which is what the ECM uses to detect bad DEF. It has to be pretty bad for this to happen. Like you let it sit in direct sunlight when it’s 140 degrees.
> 
> Needless to say… Stored in a cool dark place…. DEF will outlive you, your kids, and their kids.


True, it does, but it takes heat to make it ammonia


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