Help me to understand DEF usage. Please
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Senior User
Joined: Aug 2015
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Help me to understand DEF usage. Please
I'm just over 1000 miles AFTER the 500 mile warning. I always wait until I see the 200 mi warning before adding the DEF. It allows me to monitor and make sure that the level sensors and warnings are all working. Some weeks ago I got the 500 mile warning. We were planning on leaving for a camping trip with our travel trailer so I picked up a bottle of DEF to have on hand when the
200 mile warning came up. Here I am more than 1000 miles later and no further warnings have shown. When I check the level on the dash it only tells me "Less than 1/2". So, I'm prepared should I run out and go to limp mode but so far all's well. Please help me to understand what's happening here. Prior to this current trip my driving was local, low speed around town and had been for quite awhile before the 500 mile warning. Since then (traveling) I'm doing hard highway driving and towing an 8k trailer so my truck is working harder. While working harder it seems I see fewer exhaust cleaning cycles. Am I correct in assuming that while working harder there is LESS DEF usage due to higher operating temps and therefore what I do have remaining in the DEF tank is going to last longer ????
Thanks all, Happy travels
Roger from NJ
200 mile warning came up. Here I am more than 1000 miles later and no further warnings have shown. When I check the level on the dash it only tells me "Less than 1/2". So, I'm prepared should I run out and go to limp mode but so far all's well. Please help me to understand what's happening here. Prior to this current trip my driving was local, low speed around town and had been for quite awhile before the 500 mile warning. Since then (traveling) I'm doing hard highway driving and towing an 8k trailer so my truck is working harder. While working harder it seems I see fewer exhaust cleaning cycles. Am I correct in assuming that while working harder there is LESS DEF usage due to higher operating temps and therefore what I do have remaining in the DEF tank is going to last longer ????
Thanks all, Happy travels
Roger from NJ
Posting Guru
Joined: Dec 2015
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DEF has nothing to do with regens. DEF is used constantly while driving in very small amounts sprayed into the SCR to reduce NOx. Usage is probably somewhat dependent on how hard the engine is working as in more is used while towing. I am not sure why you don't just fill the tank and not worry about it for 3500-5000 miles? It sounds like you are micro managing it.
Edit: After viewing the video below, I see that SCR is used to reduce NOx created by the heat of a regen, so frequent regens do increase DEF usage. The video also confirms my practice of locking out gears to increase my RPMs and shorten the regen time by keeping RPMs around 2000 during regens. This could also explain why a tune that raises the shift points also decreases regen frequency.
Edit: After viewing the video below, I see that SCR is used to reduce NOx created by the heat of a regen, so frequent regens do increase DEF usage. The video also confirms my practice of locking out gears to increase my RPMs and shorten the regen time by keeping RPMs around 2000 during regens. This could also explain why a tune that raises the shift points also decreases regen frequency.
Lead Driver
Joined: Nov 2005
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From: Kaysville Utah
I rarely look at my DEF level. When I'm at a station that has DEF at the pump. I top off. Sometimes that's 1 gallon, Sometimes it's 4 gallons. Just depends on how long it's been since I added DEF. But I don't watch the gauge or worry about how full or how empty it is.
Post Fiend
Joined: Mar 2007
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From: Texas
The DEF 500 mile warning isn't always accurate (or is rarely accurate) and sometimes shows up for no reason whatsoever. I've had it pop up on mine and gone a couple of thousand more before it showed up again and started the real countdown.
The rods and super smart computer used to determine (guess) the DEF level are subject to all sorts of inaccuracy, which is why so many suggest waiting until you get below 200 miles to empty before refilling it.
The rods and super smart computer used to determine (guess) the DEF level are subject to all sorts of inaccuracy, which is why so many suggest waiting until you get below 200 miles to empty before refilling it.
6.7 Weight Loss
Joined: Jun 2017
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From: Woodbury CT
It drives me absolutely nuts that some rocket scientist at Ford decided it was a good idea to install a tank which is used for a consumable liquid and not put a gauge in the truck.
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Post Fiend
Joined: Mar 2007
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From: Texas
to avoid being embarrassed by how inaccurate their gauge would be.
At least that's how I see it.
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From: Woodbury CT
That makes me even more nuts - they've been measuring fluid levels since the 1900s - yeah I know, I totally don't understand the nuances of the def system and I get they don't want you adding def until its low, but put a 'don't add' decal on the gauge - anyway - I hijacked this thread whining about no def guage - sorry
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After reading a lot of posts about DEF and when to fill up and problems with others having their pickup shut down on the side of the road it seems best practice to to wait until it says DEF is below half then fill up. Don't worry so much of trying to get it way down but not to limp mode. It is somewhat arbitrary in that the engine uses DEF based on how hard the engine works. SO if you get the 500 mile mssg but then go back to round town driving and the engine isn't working hard, well the computer isn't going to recalculate it. Kind of like the on board fuel efficiency. If you look at it after you have been towing it will be low and if you don't reset it once you quit towing it still is going to say you are getting 11 or 12 or whatever it was when you may actually be getting 16 or 17.
Posting Guru
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My practice has been to add a jug at the 500 mile warning and it only let me down once when I couldn't get a complete jug in the tank. Then I added DEF Status to my Edge Insight CTS gauges and, with the knowledge it is not accurate, add a jug after it has been reading 66% for some time, like a couple of weeks at my current low level of driving. This has worked as I can always get a jug in the tank.
Post Fiend
Joined: Mar 2007
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From: Texas
Problem is, DEF freezes so they can't use the tried and true float mechanism. (well they could, they just choose not to deal with the frozen float issue).
So they use 2 metal rods (that get all sorts of scaling, corrosion, junk, or maybe just black magic on them) and they try to infer fluid level based on some electrical reading between the two. The computer also tries to keep things on track with some form of new math or something else incomprehensible.
What we do know is, less than half full does not mean you can add a jug of DEF to top it off. And less than 300 miles to empty does not mean you can add 2 jugs to top it off. I've even read someone who's countdown went to 0 and he didn't go into limp mode because there was apparently still DEF in there.
I got tired of washing the truck off after trying to fill DEF so I gave up trying to understand and just started following the advice on here as to when to add.
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Joined: Aug 2008
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From: Frederick, MD
use the ford fill spout, no drips. Compatible with blue def or other jugs. Rinse and reuse.
I don't fill up my def till it is less the 200 miles to empty. Towing, unloaded or whatever I never fill up till then and it always takes just under 5 gals.
I don't fill up my def till it is less the 200 miles to empty. Towing, unloaded or whatever I never fill up till then and it always takes just under 5 gals.
Thread Starter
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Senior User
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I began this thread with my original question. I'm just about at 4000 miles since my last DEF fill and MORE than 1000 miles since I had the 500 mi warning appear. Perhaps it was a fluke when it showed up but I'm still looking for the 200 mi warning. The only reason I wait is to make sure that the warning are reliable so we'll see how it pans out.
These past few months have been a mix of driving with / without our travel trailer and I'm just curious to see how the DEF consumption is.
ThanX all for the discussion and advise.
These past few months have been a mix of driving with / without our travel trailer and I'm just curious to see how the DEF consumption is.
ThanX all for the discussion and advise.