Javi's Rules for DEF Usage..
Post Fiend
Joined: Jun 2004
Posts: 9,293
Likes: 10
From: Parker, CO
Yes, I've read the manual (actually the diesel supplement) and again there is nothing in the wording that warns against filling before empty... nor is there in the '12 or the '15 manual..
The engine control unit will monitor the amount of fluid available in the DEF tank.
Running a system check in the information display will indicate whether the DEF level is ok or if it is less than 1/2 full. A message will display in the information display when the DEF level is low and needs to be refilled. When you see this message, you should refill your tank.
I see nothing about the above statement that indicates waiting until the tank is empty or nearly so before refilling or that damage will occur if one fills more often.
Again, as I said above... nothing in my facetious original post indicates that I advocate filling at every fuel stop, although there is no indication anywhere in the supplied documentation that doing so will potentially cause damage to the DEF system .
I personally refill the DEF shortly after I get the "LESS THAN 1/2" warning and I top off before a trip of any real distance towing my 5'er... I do not fill at each fuel stop...
But I do see a lot of folks who either forget or refuse to refill as directed in the manual who have gone into limp mode or even into idle only as my neighbor in the campground did a couple of weeks ago. And yes even after pouring DEF into the tank it took a tow to the dealer to reset the computer.
From your posts I would guess that you are a tech at a dealership and feel somehow compelled to correct me... You might also correct the technical writer at Ford as well as their engineers. But m[/FONT][FONT=Arial]aybe your time would be better spent educating the new diesel buyers at your dealership on how to check the DEF level so they don't have problems..
The engine control unit will monitor the amount of fluid available in the DEF tank.
Running a system check in the information display will indicate whether the DEF level is ok or if it is less than 1/2 full. A message will display in the information display when the DEF level is low and needs to be refilled. When you see this message, you should refill your tank.
I see nothing about the above statement that indicates waiting until the tank is empty or nearly so before refilling or that damage will occur if one fills more often.
Again, as I said above... nothing in my facetious original post indicates that I advocate filling at every fuel stop, although there is no indication anywhere in the supplied documentation that doing so will potentially cause damage to the DEF system .
I personally refill the DEF shortly after I get the "LESS THAN 1/2" warning and I top off before a trip of any real distance towing my 5'er... I do not fill at each fuel stop...
But I do see a lot of folks who either forget or refuse to refill as directed in the manual who have gone into limp mode or even into idle only as my neighbor in the campground did a couple of weeks ago. And yes even after pouring DEF into the tank it took a tow to the dealer to reset the computer.
From your posts I would guess that you are a tech at a dealership and feel somehow compelled to correct me... You might also correct the technical writer at Ford as well as their engineers. But m[/FONT][FONT=Arial]aybe your time would be better spent educating the new diesel buyers at your dealership on how to check the DEF level so they don't have problems..
It specifically states in the manual to "Drive Normally". In fact, the very first time it states to refill the DEF is at 500 miles to empty.
The first marker in the DEF tank is the half mark. Anything above half full and the tank CANNOT read the level of fluid. Continuing to top off the DEF as you clearly stated in your very first post in this thread can (and it does happen often) cause an error with the system reading the DEF fluid level, which causes an issue with the miles to empty countdown.
There are many threads on this very forum of people topping off the DEF and having these very issues.
Yet you, someone unknown, decides to go against Ford's recommendations (drawn up by Ford engineers who build the system), and suggest that people just ignore the owner's manual do whatever they want. Then you suggest that nothing bad could ever happen. Not only that, but you argue to the contrary, defiantly against the owner's manual which was clearly posted.
No, I'm not a tech at a dealer. I do not work at a dealership. I train dealer technicians. And people like you cause more problems for others than you are even aware of. Stop giving bad advice. If you can't be helpful, then stop creating threads full of misinformation and BS.
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Senior User
Joined: Aug 2012
Posts: 274
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From: Waco, Tx
Ok, not only did you not read the manual... but obviously you can't even read.
It specifically states in the manual to "Drive Normally". In fact, the very first time it states to refill the DEF is at 500 miles to empty.
The first marker in the DEF tank is the half mark. Anything above half full and the tank CANNOT read the level of fluid. Continuing to top off the DEF as you clearly stated in your very first post in this thread can (and it does happen often) cause an error with the system reading the DEF fluid level, which causes an issue with the miles to empty countdown.
There are many threads on this very forum of people topping off the DEF and having these very issues.
Yet you, someone unknown, decides to go against Ford's recommendations (drawn up by Ford engineers who build the system), and suggest that people just ignore the owner's manual do whatever they want. Then you suggest that nothing bad could ever happen. Not only that, but you argue to the contrary, defiantly against the owner's manual which was clearly posted.
No, I'm not a tech at a dealer. I do not work at a dealership. I train dealer technicians. And people like you cause more problems for others than you are even aware of. Stop giving bad advice. If you can't be helpful, then stop creating threads full of misinformation and BS.
It specifically states in the manual to "Drive Normally". In fact, the very first time it states to refill the DEF is at 500 miles to empty.
The first marker in the DEF tank is the half mark. Anything above half full and the tank CANNOT read the level of fluid. Continuing to top off the DEF as you clearly stated in your very first post in this thread can (and it does happen often) cause an error with the system reading the DEF fluid level, which causes an issue with the miles to empty countdown.
There are many threads on this very forum of people topping off the DEF and having these very issues.
Yet you, someone unknown, decides to go against Ford's recommendations (drawn up by Ford engineers who build the system), and suggest that people just ignore the owner's manual do whatever they want. Then you suggest that nothing bad could ever happen. Not only that, but you argue to the contrary, defiantly against the owner's manual which was clearly posted.
No, I'm not a tech at a dealer. I do not work at a dealership. I train dealer technicians. And people like you cause more problems for others than you are even aware of. Stop giving bad advice. If you can't be helpful, then stop creating threads full of misinformation and BS.
go on back to your hookah..
Super Moderator
Joined: Aug 2008
Posts: 37,375
Likes: 1,860
From: Frederick, MD
Folks, a difference in how to fill the def and what interval is a good discussion.
Everyone will interpret the manual and little differently too.
I too believe in running it down. The op believes the complete opposite. It works for him.
Its ok.
Everyone will interpret the manual and little differently too.
I too believe in running it down. The op believes the complete opposite. It works for him.
Its ok.
Senior User
Joined: Feb 2015
Posts: 268
Likes: 0
Ok, not only did you not read the manual... but obviously you can't even read.
It specifically states in the manual to "Drive Normally". In fact, the very first time it states to refill the DEF is at 500 miles to empty.
The first marker in the DEF tank is the half mark. Anything above half full and the tank CANNOT read the level of fluid. Continuing to top off the DEF as you clearly stated in your very first post in this thread can (and it does happen often) cause an error with the system reading the DEF fluid level, which causes an issue with the miles to empty countdown.
There are many threads on this very forum of people topping off the DEF and having these very issues.
Yet you, someone unknown, decides to go against Ford's recommendations (drawn up by Ford engineers who build the system), and suggest that people just ignore the owner's manual do whatever they want. Then you suggest that nothing bad could ever happen. Not only that, but you argue to the contrary, defiantly against the owner's manual which was clearly posted.
No, I'm not a tech at a dealer. I do not work at a dealership. I train dealer technicians. And people like you cause more problems for others than you are even aware of. Stop giving bad advice. If you can't be helpful, then stop creating threads full of misinformation and BS.
It specifically states in the manual to "Drive Normally". In fact, the very first time it states to refill the DEF is at 500 miles to empty.
The first marker in the DEF tank is the half mark. Anything above half full and the tank CANNOT read the level of fluid. Continuing to top off the DEF as you clearly stated in your very first post in this thread can (and it does happen often) cause an error with the system reading the DEF fluid level, which causes an issue with the miles to empty countdown.
There are many threads on this very forum of people topping off the DEF and having these very issues.
Yet you, someone unknown, decides to go against Ford's recommendations (drawn up by Ford engineers who build the system), and suggest that people just ignore the owner's manual do whatever they want. Then you suggest that nothing bad could ever happen. Not only that, but you argue to the contrary, defiantly against the owner's manual which was clearly posted.
No, I'm not a tech at a dealer. I do not work at a dealership. I train dealer technicians. And people like you cause more problems for others than you are even aware of. Stop giving bad advice. If you can't be helpful, then stop creating threads full of misinformation and BS.
I don't mean to sound like I am attacking you because I know you are just the messenger, but it surely shouldn't cause problems to keep the tank full. My guess is they saved a couple dollars each on the current set up that has probably been more than offset by warranty claims.
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Senior User
Joined: Aug 2012
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From: Waco, Tx
I understand but that sounds like a pretty stupid set up to me. Nothing else on any vehicle I have ever owned recommended that you wait until it was almost empty to fill it up. Should we wait until the engine overheats to add coolant, oil pressure drops to add oil, only fill up when the fuel idiot light comes on, etc.?
I don't mean to sound like I am attacking you because I know you are just the messenger, but it surely shouldn't cause problems to keep the tank full. My guess is they saved a couple dollars each on the current set up that has probably been more than offset by warranty claims.
I don't mean to sound like I am attacking you because I know you are just the messenger, but it surely shouldn't cause problems to keep the tank full. My guess is they saved a couple dollars each on the current set up that has probably been more than offset by warranty claims.
Yes it would be pretty darn inconvenient if you had to run the tank empty before filling it.. There is no warning about frequently re-filling the DEF tank anywhere in the manual. And yes I've read it and yes I am an engineer and yes I can comprehend what I read.
There is however a warning about carrying DEF in your truck, also a warning to store DEF in a very narrow temperature range that most of us would find impossible to adhere to if we ignored the warning to NOT carry DEF in the truck.
Admittedly the warning not to carry DEF in your truck is about corrosion caused by a leak, but the warning about storage temp ranges is about the quality and strength of the DEF. Urea will in fact breakdown (turn into ammonia) in higher temps and it will fall-out at lower temps. I spent several years dealing with this as the VP of operations for a large fertilizer storage and distributing company. One of my duties was the designing of mixing facilities to blend Urea into liquid fertilizer. Urea will make bare carbon steel oxidize with exposure. Don't get excited... if you spill a little on the truck just flush the area well with fresh water making sure to get into any seam that the Urea solution might have gone.
Back to filling the DEF tank, other than the above warnings, the only other is about over-filling in freezing weather....
There is absolutely NO warning about topping off the tank, or about waiting till the tank is empty to re-fill.. Nor is there a directive to WAIT until empty or nearly empty..
As for the flow chart... Yes.. drive normally when you get the "LESS THAN 1/2" warning.. you got another 1000 miles or so from when you first see it.. No need to whip off the highway in a panic...
The rest of the flow chart is a DUH....
wake up and fill the tank.... stupid... type of warning.. 
Bottom line... you are NOT doing wrong if you choose to wait until you get the 99 mile warning or even wait until it threatens you with limp mode before re-filling.... Although I'm not sure why you'd do that..
But you are also NOT doing anything wrong if you choose to fill at the 1/2 warning or if you top off before a long trip.. the truck doesn't care.. and if you have a problem with the level sensors in the tank, you would have had the same problem even if you waited.. they don't know you filled the tank early, they just read the level and report it...
Post Fiend
Joined: Jun 2004
Posts: 9,293
Likes: 10
From: Parker, CO
I understand but that sounds like a pretty stupid set up to me. Nothing else on any vehicle I have ever owned recommended that you wait until it was almost empty to fill it up. Should we wait until the engine overheats to add coolant, oil pressure drops to add oil, only fill up when the fuel idiot light comes on, etc.?
I don't mean to sound like I am attacking you because I know you are just the messenger, but it surely shouldn't cause problems to keep the tank full. My guess is they saved a couple dollars each on the current set up that has probably been more than offset by warranty claims.
I don't mean to sound like I am attacking you because I know you are just the messenger, but it surely shouldn't cause problems to keep the tank full. My guess is they saved a couple dollars each on the current set up that has probably been more than offset by warranty claims.
There have been calibration updates to try and address this, however it still happens.
Just know that topping off the DEF can cause problems. Not everyone will have this issue, but it's prevalent enough that people should be aware of the possible consequences should they heed the advice that is contrary to the owner's manual.
Post Fiend
Joined: Jun 2004
Posts: 9,293
Likes: 10
From: Parker, CO
There is no warning about frequently re-filling the DEF tank anywhere in the manual.
Back to filling the DEF tank, other than the above warnings, the only other is about over-filling in freezing weather....
There is absolutely NO warning about topping off the tank, or about waiting till the tank is empty to re-fill.. Nor is there a directive to WAIT until empty or nearly empty..
Back to filling the DEF tank, other than the above warnings, the only other is about over-filling in freezing weather....
There is absolutely NO warning about topping off the tank, or about waiting till the tank is empty to re-fill.. Nor is there a directive to WAIT until empty or nearly empty..
There is, however, a very clear directive to wait to fill when it tells you to fill. Not before.
But you are also NOT doing anything wrong if you choose to fill at the 1/2 warning or if you top off before a long trip.. the truck doesn't care.. and if you have a problem with the level sensors in the tank, you would have had the same problem even if you waited.. they don't know you filled the tank early, they just read the level and report it...
The first marker is the half tank point. Anything above that and there is no sensor to detect the level of DEF above half tank. It doesn't work like your fuel tank where it constantly reads the current level. It can only see if the level is above or below a fixed point.
The sensors can work perfectly fine, and you can still have a problem if you continually top off the DEF. Eventually the PCM will freak out and assume that something is wrong with the sensors, and will decide to count down regardless of the tank level. The sensors are still reporting a full tank, but the system thinks there has to be a problem somewhere. If the DEF level never drops, eventually the system forces a miles to empty countdown. At that point you'll have to take it to the dealer to have it reset, which will come at a cost.... especially if you're out of warranty.
Now if you let it drop below half tank regularly, most likely you'll never once have an issue. And that could be why you and others never see this problem. Because at least one sensor is reporting a drop in the DEF level to the PCM, keeping things happy and working as normal.
But again, it was YOU who suggested that topping it off even at above half full will not cause a problem. THIS IS NOT TRUE, AND I'M SIMPLY WARNING OTHERS READING THIS THREAD THAT THERE COULD BE POSSIBLE ISSUES FOLLOWING YOUR ADVICE.
Post Fiend
Joined: Jun 2004
Posts: 9,293
Likes: 10
From: Parker, CO
Continually topping off the DEF can cause problems. People must be made aware of this if someone is going to come on this forum and give them advice to the contrary. That's all.
If someone understands the potential consequences and still decides to top off the DEF, that's fine. It's their truck they can do what they want. But the responsible thing is to at least give people the opportunity to understand all risks before doing so.
Furthermore, to blatantly be defiant about it is just gross negligence and disrespect to all the members on this forum. That's why my responses to him are a bit prickly.
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Thread Starter
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Senior User
Joined: Aug 2012
Posts: 274
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From: Waco, Tx
I understand, but what's not ok is delivering advice to others without fair warning of potential issues, and failure to deliver the warning because that person giving the advice is not fully familiar with how the system operates.
Continually topping off the DEF can cause problems. People must be made aware of this if someone is going to come on this forum and give them advice to the contrary. That's all.
If someone understands the potential consequences and still decides to top off the DEF, that's fine. It's their truck they can do what they want. But the responsible thing is to at least give people the opportunity to understand all risks before doing so.
Furthermore, to blatantly be defiant about it is just gross negligence and disrespect to all the members on this forum. That's why my responses to him are a bit prickly.
Continually topping off the DEF can cause problems. People must be made aware of this if someone is going to come on this forum and give them advice to the contrary. That's all.
If someone understands the potential consequences and still decides to top off the DEF, that's fine. It's their truck they can do what they want. But the responsible thing is to at least give people the opportunity to understand all risks before doing so.
Furthermore, to blatantly be defiant about it is just gross negligence and disrespect to all the members on this forum. That's why my responses to him are a bit prickly.
I really wasn't getting anything out of it anyway... I get in my truck and drive it without obsessing about what will break today..
Logistics Pro
Joined: Jan 2013
Posts: 3,778
Likes: 153
Let's work on the assumption that I'm not suggesting topping it off every 20 miles.. Okay..
It works on the dilution factor... the tank is 5 gallons... pour a gallon in to fill it and you've diluted the old DEF with new DEF by 1/5th or 20%
2 1/2 gallons to fill would be a dilution factor of 50%...
So with my truck I'm diluting the old DEF with New DEF at a 50% ratio every couple of weeks, I really don't think shelf life come into play here.. or for most of us for that matter. Now if you park your truck for months at a time, especially in weather below freezing then it certainly might come into play.
Another thought occurred to me as I was typing this..
For those of you advocating running the tank dry or nearly dry... what you think about the sediment in the bottom of the tank from the Urea coming out of solution in cold weather... it is after all a solid dissolved into a liquid.
It works on the dilution factor... the tank is 5 gallons... pour a gallon in to fill it and you've diluted the old DEF with new DEF by 1/5th or 20%
2 1/2 gallons to fill would be a dilution factor of 50%...
So with my truck I'm diluting the old DEF with New DEF at a 50% ratio every couple of weeks, I really don't think shelf life come into play here.. or for most of us for that matter. Now if you park your truck for months at a time, especially in weather below freezing then it certainly might come into play.
Another thought occurred to me as I was typing this..
For those of you advocating running the tank dry or nearly dry... what you think about the sediment in the bottom of the tank from the Urea coming out of solution in cold weather... it is after all a solid dissolved into a liquid.
As an adjunct to the above or 'last straw in my 45' motor coach saga':
Took delivery of our motor coach and listened intently and the sales guy when thru all the features. One of my points of interest was the drive train and spec. One spec was the fuel tank which was 150 gals. In fact that was on the spec sheet and had to be set in the trip computer on board as many models have different size tanks.
Later: On a trip, I opted to travel on to El Paso rather than stopping. I checked the trip computer and it showed I had about 150 miles before empty.
The rig lurches and bucks I manage to pull over on I 10. Rig will not start, so I call the mfg. After much discussion etc he ascertains it out of fuel. CAN'T BE!!! He asks me to check the settings on the trip computer and its set for a 150 gal tank.
Long pause: Sir, you do have a 150 gal tank, but you can only assess the first 100 gals.
ARE YOU FIGGIN KIDDING ME??? WTH!!!
Well sir, the last 50 gals where the sediment and water is at!
Finished trip, drove into dealer where I bought it and told them the love is gone, buy it back!
Senior User
Joined: Feb 2015
Posts: 268
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Unfortunately it can cause problems, and it does. Next to exhaust temp sensor failures, DEF resets are one of the most common reasons people bring their 6.7L's into the shop. And the primary cause? Continually topping off the DEF.
There have been calibration updates to try and address this, however it still happens.
Just know that topping off the DEF can cause problems. Not everyone will have this issue, but it's prevalent enough that people should be aware of the possible consequences should they heed the advice that is contrary to the owner's manual.
There have been calibration updates to try and address this, however it still happens.
Just know that topping off the DEF can cause problems. Not everyone will have this issue, but it's prevalent enough that people should be aware of the possible consequences should they heed the advice that is contrary to the owner's manual.
Post Fiend
Joined: Jun 2004
Posts: 9,293
Likes: 10
From: Parker, CO
So let me see if I have this straight. The def system is a 'dumb' system kind of like a carburetor vs fuel injection. The def system sprays in urea in rough estimates based a on a couple parameters and relies on the tank sensors as an input to determine that the def system is spraying in an acceptable amount of urea. When it never gets the input that urea is being used (half tank warning or whatever level) it goes into a fault mode that requires dealer servicing - probably for epa purposes.
The "dumb system" is the level indicator.
The actual injection is controlled by completely different parameters. That system is much smarter.
In other words, the level indicators do not determine how much DEF is spraying, or if it's an acceptable amount. They only track how much fluid is in the tank, and when it needs to be refilled. How much is actually injected is determined by other engine/exhaust sensors and calibration programming.
Senior User
Joined: Jul 2014
Posts: 263
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From: Rural Sumter Co. Georgia
On a lighter (?) note, a friend told me he took his wife's Mercedes diesel for routine service. He said he was charged $83 for one gallon of DEF. Just be thankful we don't require "Mercedes DEF" in our trucks!
He did not say if that included the labor involved with pouring it into the tank.
He did not say if that included the labor involved with pouring it into the tank.
Super Moderator
Joined: Aug 2008
Posts: 37,375
Likes: 1,860
From: Frederick, MD
On a lighter (?) note, a friend told me he took his wife's Mercedes diesel for routine service. He said he was charged $83 for one gallon of DEF. Just be thankful we don't require "Mercedes DEF" in our trucks!
He did not say if that included the labor involved with pouring it into the tank.
He did not say if that included the labor involved with pouring it into the tank.
Let them know I'd be happy to charge the same just to "pee" in the tank.