Used 2021 AT4 with 3.0 DEF question.

[brisk00]

I just bought a used 2021 AT4 with the 3.0 with about 3,800 miles.  This is my first diesel but I have read a ton of documentation, forums and Facebook groups specific to the 3.0 Duramax.  When I got the truck I scrolled through all of the information in the DIC.  I noticed that the DEF gauge is a about a third full.  I figured the previous owner may have done a lot of towing with it because at 3,800 miles it should not be that low.  Am I correct in that assumption?  Should I go ahead and fill it up or wait until the truck tells me to?  How much do I fill it? Until full?

 

Thanks!

[mjonesjr84]

Fill it up until full. Best bet is to stop a truck stop and use the big truck pumps with the DEF dispenser. It will click off just like a fuel pump when it is full. GM says that a full tank will get you about 5,000 +/- miles. I bet the dealer didn't fill it up all the way when they sold it originally.

[brisk00]

Awesome.  Thanks!  There are 2 places near me that have DEF at the pump.  A Buccee's and a Pilot.  Do you think these would be able the same quality?

[mjonesjr84]

17 minutes ago, brisk00 said:

Awesome.  Thanks!  There are 2 places near me that have DEF at the pump.  A Buccee's and a Pilot.  Do you think these would be able the same quality?

 

I believe there is only a couple DEF manufactures in the US. As long as they have constant use on their DEF, I'd think so. DEF does have a short shelf life.