Def system
Tuned
Joined: Sep 2016
Posts: 347
Likes: 12
Only weird thing I had was that I let it run down to 50 miles remaining before it went into limp mode, and when I refilled it full at a truck stop, it didn’t register it was filled up at all. Got back on the interstate thinking it just took time, but ended up pulling back off the road and doing a power cycle before it finally started to “fill up”. It “fills” very slowly over a couple minutes, unlike your gas tank. Other than that, it truly sips DEF unless you’re towing. I have 13,000 miles on my 2017 and I’ve only filled it up twice.
Logistics Pro
Joined: Feb 2005
Posts: 3,529
Likes: 390
From: SEVA
If you're questioning the DEF system's longevity, perhaps you'll get some higher mileage replies if your question was asked in the 1999-2016 Super Duty forum. I believe DEF has been mandatory beginning with the 2011 diesel models. It's not a system specific to 2017-up models.
Fleet Mechanic
Joined: Dec 2012
Posts: 1,563
Likes: 533
From: DFW
Near 26,000 miles on my 17 - warranty started counting down in Sept. of 2017. No issues except for the slow-gauge register mentioned above. Both the dash gauge and the gauge on my CTS2 are slow to register a refill. It’s on-tap at the QT near me so, that’s real nice.
FTE Community Team
Joined: Mar 2017
Posts: 3,337
Likes: 1,050
From: Florida
A friend with a 2015 has had issues with DEF. Twice they waited until it was very low then added it. Shortly afterwards it went into limp mode. This was particularly disastrous because they were towing a horse trailer full of horses on a 90 degree day.
I therefor always add DEF as soon as it gets to 1/2 tank and dump in a 2-1/2 gallon jug.
I therefor always add DEF as soon as it gets to 1/2 tank and dump in a 2-1/2 gallon jug.
Cargo Master
Joined: Oct 2015
Posts: 2,745
Likes: 72
From: West Virginia
I'm at 55,000 miles with no issues. Twice, I've let it get down to the point it tells me I have 500 miles worth of DEF remaining in the tank before filling. I try to keep it over 1/4 tank for the most part.
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Junior User
Joined: May 2018
Posts: 51
Likes: 1
From: Lubbock, TX
Just rolled 26k miles on my 17. No issues here. I usually dump a 2.5g jug in when it gives me the 500 MTE warning.
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Laughing Gas
Joined: Jun 2018
Posts: 939
Likes: 8
From: DFW
Have not had to add any yet to my 18 but on my past oil burners just let it go to half full or a little lower and add a big box of the Blue DEF... Truck before this one was a Cummins and had a smaller tank than the new Ford SD's..
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