So I've noticed the DEF gauge over the last couple thousand miles is all over the place. I have had no errors or codes, no performance issues I'm aware of. Only thing that has changes is extended idle time (cold weather wamups) but my DEF gauge has been reading as low as 2,500 miles, and as high as 7,500. Previously it would top out at 6,500 and fall consistently with each DPF cycle, roughly 500 miles every 500 miles. Just this week it went from 3,000 to now 7,500 while reading just over a quarter tank. I had it filled roughly 2,000 miles ago on the las toil change and it should be at or just below the 3/4 mark of DEF.

Is this a precursor to something going bad in the DEF system? If anything the truck is working harder right now, between towing my enclosed trailer, plowing, and higher idle times. It should be using more DEF, not less, right???

 

 

You are over thinking this. Just drive and when it gets low fill it. Or if you know you are going to tow for a distance. Top it off before you go.


DEF is used to reduce NOx. NOx is produced by High EFT temps. You putt putt around town empty, and your EGTs will be 500° and no DEF will be consumed. You tow 13,000ls up a 7% grade and your EGTs will be 900° and you will consume DEF.
Add in Cold winter weather where you DEF might Freeze. It basically shuts off the DEF system until you reductant heater thaws it out and your distance per tank can be increased. Doesn't mean it stopped working. It is doing exactly what it was designed to do in the cold.

On my 2020 truck. 70 mph on the freeway, my EGTS are 490-520° You just are not getting hot enough EGTs to make NOx and won't be consuming DEF.
If you don't have gauges to show your EGT's. Think of it this way. Unless you've got substantial turbo boost, you don't have NOx

 

Get an iDash and set it up and never worry about it again. Just watch the DEF level and fill when it gets low.

 

@speakerfritz has a 19 F450 and has posted on problems like this on his truck with his DEF level gauge... he'll probably chime in.

Appreciate the info bud...

I do remember I got it here, to check every 3k to 4k miles to keep the fluid on the heater... about 2.5 gallons. I did that and my DEF heater still got replaced around 40ish k miles...

I just daily drive my truck, 18 miles on way to work with some 65mph highway driving, so I'll quote some figures from notes I keep on mine (yeah, I have a problem...) I use the Motorcraft factory fill nozzle...


11/16/19 50167 miles 500 mile warning light on... filled with about 4.5 gal

02/15/20 54885 miles filled with 1.75 to 2 gal what was left in bottle

02/23/20 55369 miles filled up tank with about 1.25 gal out of new jug

05/03/20 58116 miles added about 1.25 gal out of same jug

07/22/20 61490 miles checked DEF level -- said under half

07/23/20 61550 miles filled up with about 2.5 gal or so

10/09/20 64731 miles added about 2.0 gal, if that, did not fill tank

11/12/20 66259 miles filled up tank with 2.5 gal

02/25/21 70205 miles DEF level under half tank. added about 2.5 gal; said DEF level OKAY after.

04/14/21 72568 miles filled tank with 2.5 gal. opened a new jug and took none....


My average per year based on my years of ownership and 101k miles now, I average almost 17 k miles just daily driving... and that has included some trips to KY in which we haven't done due to Covid. I do live in the hills south of Buffalo so I do get the EGTs some what hot... regens performed on a local expressway that climbs those hills as it heads south...

Just wanted to post that up, my notes, so people can get an idea of DEF usage but the new trucks use MORE DEF from what I understand as what's been discussed here.

 

Way over thinking this def stuff. Run it down to <200 to empty. Fill it full and drive on.

Newer trucks consume more than older trucks. So when I tow I switch gauges from boost to def. and then monitor it.

 

Another couple hundred miles and another warm day. This thing really is all over the place.

 

The gauge level barely moved, only the estimated distance to empty has adapted to your current driving/towing habits. Makes sense if you are towing heavy enclosed trailer + plow work.

 

Literally only a couple hundred miles, and no plowing or towing in that range. Normal (non-interstate) highway driving to/from work.

 

Are you in a cold climate? DEF freezes at 12 degrees F. Mine has been doing the same thing when it gets cold. I know there is a DEF heater on the truck but I am not sure if it is on when the truck is sitting. I know that I took a 350 mile trip in the cold and when I started the trip DEF was at 1/4 tank and when I ended it read almost full. (I filled the DEF before I left). Truck is at the dealer right now and they are looking into it. I am not sure that they know how the system heater works.

 

This would not surprise me one bit! LOL It is rare to find a dealer mechanic who is fully up on all aspects of operation.