DEF can I drain the tank?

Eastwood

Member
May 18, 2021
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I just bought a new 2021 GMC Sierra 1500 Denali 4x4 crew cab and really happy with the power the 3.0 diesel has. I'm concerned about the def fluid since I rarely put over 7,500 miles on my vehicles per year. Is there someway to drain the def tank on the truck so that I can put fresh def fluid in if needed?
 
Not sure but you may be able to siphon it out. Then put a fresh bottle in it. I don’t know if they have an anti-siphon valve on the DEF tank but I doubt it.
 
I’m in the same boat as you with how many miles I will put on in a year and was wondering the same thing
 
Not sure but you may be able to siphon it out. Then put a fresh bottle in it. I don’t know if they have an anti-siphon valve on the DEF tank but I doubt it.

Yep, here's a economical harbor freight option:
 
Yep, here's a economical harbor freight option:
I am thinking that device won't work too well. The solid black tube is the inlet to the pump.

I haven't looked, but it would take some mighty flexible hose to get from the filler neck all the way over to the passenger side of the frame, where they mounted the def tank.
 
I am thinking that device won't work too well. The solid black tube is the inlet to the pump.

I haven't looked, but it would take some mighty flexible hose to get from the filler neck all the way over to the passenger side of the frame, where they mounted the def tank.

Good point! I didn't think about the routing underneath.
 
I go through about 2.5gal DEF every 2500 miles. Not alot of towing. I would just let it run down low and fill or half fill and just add more often. You'll go through a tank of DEF in 7500 miles. I can't see it going bad in a year.
 
I will have to crawl under it tomorrow and see if I can find a drain plug
I’ve looked as well with the same concern. Worst case is drop the tank or try and get some real small hose all the way to the tank from the filler.
I havnt been able to find a schematic for the stuff (pump maybe?) mounted under the cover on the bottom of the tank to see if that’s a easy way to drain.

ive always made sure I buy super fresh def. usually find a box that’s no more than a month old. And in the summer I don’t drive it daily so I will get the level down to 10-15%. Then fill it before or around winter.

any time def is over 80 it will slowly start to degrade and less that 60 it has a 2+ year life span. so winter I’ll have it full with no risk of it going bad. And summer I maintain a smaller amount.
Keep in mind if I was to take my boat or any trailer 5-6 hrs away. I wouldn’t leave at 15%.
Over the past 10k now I average 1000mpg for empty driving
500mpg for towing my small trailers and boat.
Overall ive used 8 gallons in 10k miles
 
Bought my truck 2021 RST 3.0 at the end of June, have a bit over 7000 miles now, added 2.5 gals at my free oil change provided by the dealer at 3000 miles.
it still at one notch below half, many days over 90deg plus? and the def is no good now??? seems weird, I also can't find any drain on my DEF tank?
I think I have used just around 3 gals in 7000 miles I guess.
 
I’ve looked as well with the same concern. Worst case is drop the tank or try and get some real small hose all the way to the tank from the filler.
I havnt been able to find a schematic for the stuff (pump maybe?) mounted under the cover on the bottom of the tank to see if that’s a easy way to drain.

ive always made sure I buy super fresh def. usually find a box that’s no more than a month old. And in the summer I don’t drive it daily so I will get the level down to 10-15%. Then fill it before or around winter.

any time def is over 80 it will slowly start to degrade and less that 60 it has a 2+ year life span. so winter I’ll have it full with no risk of it going bad. And summer I maintain a smaller amount.
Keep in mind if I was to take my boat or any trailer 5-6 hrs away. I wouldn’t leave at 15%.
Over the past 10k now I average 1000mpg for empty driving
500mpg for towing my small trailers and boat.
Overall ive used 8 gallons in 10k miles
DEF degrading when over 80 (degrees Fahrenheit I presume). My stepson said that there is a problem with Blu DEF brand DEF causing problems and codes when used in GM vehicles in the Southwest (So CA, AZ, NM, west TX, 100°+ several months of the year with 20% humidity). DEF “calcifies” and coats the inside of the tank, the sensors, and clogs the jets. He had his entire DEF system replaced (warranty) because of it. Autozone and Walmart “house” brands don’t seem to have the problem. My 2020 Chevy has been throwing DEF related warnings on the DIC (“Service Emissions System”, “174 miles before speed limited to 65 mph” but DEF gauge is showing 35%-95% full). Am having dealer check it out.
 
The urea should go back in to solution I would guess. unless the def tank is an open system and water is evaporating to cause urea to crystallize out. I hope that wouldnt be the case.
 
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