Had my first oil change yesterday at 4960 miles. DEF gauge was at the 1/4 tank mark which I felt was good. I then added a box (2.5 gal) of the Blue Def fluid and the gauge went up to 5//8 of a tank. Drove up and down the street but it stayed at 5/8. Not trying to split hairs but if the DEF tank holds 5 gallons and I add 2.5 to a 1/4 tank I was expecting a solid 3/4 on the gauge. No?

Also, when I was done there were a few drops of DEF fluid on the truck and on the ground that crystalized? What stops this stuff from crystalizing inside the tank?

Thanks

 

The dead on accurate gauge I think is a thing of the past ..
DEF is water based evaporation will make it crystalize ..

 

DEF tanks is 7.5 gallons.

 

Def is urea it's harmless. keep your tank cap tight and better yet keep it filled up. the less air it's exposed to the better.

 

Then gauge is about right. So when gauge reads about half it’s best to fill it? That would be about 3.5 + 2.5 = 6. Read someplace to make sure it’s not overfilled but I’m guessing that’s just for winter expansion.

 

This was taken (picture is terrible but you get the idea) when the fluid in the truck was about seven months old. Ideally, you want the spec at 32.5% so this is after sitting in the truck from Jun-Jan so not a whole lot of evaporation even though we have temps in the high 90 - low 100s for several of those months. If you wanted to take the time and screw with it, you could figure out how much distilled water you could add to bring your DEF back into spec given how much DEF you currently have in the tank. It would have been nice to place a drain on the DEF tank for those that don't use the truck much in the off-season or store the truck for prolong timeframes so you could refill it. Granted, you can drain it by siphon but a drain would be the better option.

 

Is it true the tank should be drained every 10k miles? Guess that's to keep the DEF fresh so it doesn't crystallize? Looks like I'm going through about 5 1/2 gals in 5K miles. If I can get my brain working and figure out when (thinking it's when gauge reads 1/2 tank) I'll add the 2.5 gals to keep the tank full. I guess if it's just a matter of waiting until low and running a small tube down the line into the tank to remove it's not that big a deal. I agree if it needs to be done on a regular timeframe a drain plug would have been nice.

Anyone have a link or can post a picture of the DEF tank on the truck? Is it just a basic storage tank like the windshield washer holder or more to it? Also, if you drain the tank that is going to let air into the holding tank which will allow the residue to crystalize? Does it dissolve once you add fresh mix to it?

 

I would not worry about draining it unless the truck was going to sit for an extended time. Like a year or more. I bought my truck in Nov 19 and it had been at the dealership since Jun. It basically sat for six months and then I did not add any DEF until Jun 20 for a trip back to WY. I would go by the time the truck sits and not mileage as some folks put 10k a month on these and never drain the DEF as they are putting in fresh DEF all the time.

 

the def gauge is useless. mine fluctuates 1/4 of the dial thruout the day.

I initially was of the "keep it full " school. but now....my thinking is keep it full spring, summer, fall, then plan your consumption so that its 1/4 below full in the winter. if you fill it up during the winter...you are likely to join the "def tank cracked" club .

and premium blue def does not behave (dial indicator) any better than the cheapest def you cam find.

 

I am trying the premium as it's claimed to reduce the amount of deposit build up over regular DEF. Does it work, who knows. How can I test it without tearing the system apart, I can't really. Maybe over time it might help a bit. Kind of like placing a "tactical" label on stuff. It will double sales. Kind of like adding "premium" as in "better" but like most stuff, it may not make a difference. I am in the low-use DEF club so the increased cost is not an issue.

 

If you read it on the Internet, it must be true.

I don't tow. I don't do any heavy hauling. My truck spends most of its life sitting in the driveway. The DEF in my tank is what the factory put in there back in February 2018. I'm down to a bit over a half a tank. I've never even taken the cap off the tank. I'm sure that when I trade it in a couple years from now, that DEF will still be in the tank. I can't imagine what mileage has to do with DEF. Sounds like some Internet experts just makin' stuff up.

 

Drive truck.
Add DEF when needed.
Sleep at night.

Lots of over thinking worrying about this. I keep DEF in my carport for several months sometimes in the AZ heat. Never an issue.

 

Like C12H24 I use very little DEF. At 9k miles the gauge still showed just over 1/4 tank. It wasn't until 27 months from build date, 22 months after purchase that I added 2.5 gal., to freshen it up.

 

what is premium def? What are you using that makes it premium?

 

I think all def is made by like 2 places. Can't imagine anything premium about one brand over another other then price.