DEF Tank, Top It Off or Run Empty?

[Ziggy]

Looking for your best practices. My truck isn't my daily so it takes a good bit of time before I need to refill my DEF. Example, purchased truck end of January this year and just yesterday put a 2.5 gallon jug in it. Is it better to keep the tank on the fuller side (without overfilling) to reduce the amount of air and possible crystallization inside the tank or don't worry and just fill as needed when I reach 1/4 tank left?

Expiration is the only issue. DEF has a shelf life so I let my tank go to at least 1/4, then top off at a station that has DEF pumps.

 

[jebruns]

The sensor in the 19+ trucks have been known to throw a P203E when overfilled. There is a TSB on it.

https://static.nhtsa.gov/odi/tsbs/2021/MC-10194039-9999.pdf

I wonder if ZD4 fixed that. At any rate, I have never thrown an error code, of any kind, in my '22. And I filled the DEF up to the tippy top at least twice now. The TSB also mentioned other reasons for throwing those codes.

 

[mbarber84]

I’ve found best practice is run the tank down to 1/4, then put a 2.5 gallon jug in which will take the tank back to 3/4 full. This strategy keeps the sending unit submerged at all times and reduces the risk of crystallization down low in the tank. It also prevents the possibility of overfilling the tank, or In temperatures below 12°F, also prevents the possibility of the fluid freezing and expanding to the point that it eliminates the air gap between the top of the fluid and the top of the tank. The level sensor in the sending unit uses a sonar echo to detect fluid level. If the tank is overfilled to the very top (or if the fluid freezes and expands into that area) the echo does not return correctly and the sensor won’t be able to read the level. You’ll end up with DTC P203E.
I have utilized the 1/4 - 3/4 approach on both of my trucks (2017 and 2022) and have had zero DEF problems. I’ve religiously used the BLUE platinum DEF and always check the date codes printed on the box. Buy and use stuff that has the longest shelf life based on interpretation of the date code. When you buy the jugs, buy them from a shelf inside the store, not ones sitting in direct sunlight or in the air locks in the front of the store where the temperature increases / decreases depending on the season.

 

[JD2510]

When you Google DEF on the internet there are only a handful of companies the produce def, all of them are required to follow same guidelines. Since 2018 I have also used the same practice of when def tank gets to 1/4 add 2.5 gallon. I go to Rural King and purchase the plain box that just say DEF for $8.99 it was $6 when I started using it. Put the same type in our tractors without any issues. The only difference is on Sunday you won’t see Prime Guard Ultrapure DEF going around the track on a NASCAR but you will see blue box brand.