I really think the issue here is that the owners manual isn't smart enough to update to the latest information that Ford has. Else there would be a "suggestion" to allow the system to run below 1/2 a tank of DEF before refilling to keep the system calibrated.

Bill

 

You are too late. I already have the contract.

 

While I would not say I continually top off, I do add 2.5 gal when its gets to less than half full, just like I generally fill up when I get below a half tank of fuel.

I brought your concerns up to the folks at Ford and where I trade trucks are the major % of their business. It was not a long discussion (but will be next time I go down there), they just told me no problem on doing it that way. I will get more in depth later.

In Javi's defense I took his "rules" as a more tongue in cheek' humorous comments. I did not feel it was written with the degree of 'presenting fact'. I do agree, that presenting advice that will lead to failure, safety or warranty issue.

 

I may be the naive one here but isn't it just as simple to follow the IOLM and fill the DEF at the time of an oil change?

Ford designed the system to try to be as least as intrusive as it could be to the owner, there is absolutely no need to fill between OC's if you're following the IOLM.

 

And if you allow it to go at least below half full, then at minimum it's reading the first level marker. So in all likelihood you won't have an issue. Safest bet is always to follow the owner's manual recommendations and instrument cluster messages.

Most dealers and shop technicians don't even know this can be a problem. They just see a truck coming in with a full DEF tank and the countdown to empty. Hook up IDS and reset and charge labor time. They don't typically talk to the customer or ask why it happens, and most service writers have never been informed that this can be an issue.

The DPF has adaptive learning tables. Like anything that has adaptive learning, an error somewhere can throw it into a loop that requires a reset. This is similar to what is seen with the DEF miles to empty countdown. If it thinks there's an error somewhere, it will continue to count down until it sees a change in the fluid level, or until the parameters are reset. Usually the miles to empty counts down faster than the fluid level can fall to reach the next level indicator.

So how does it work in the case of the DEF system?

It starts with knowing how the level indicators function and where they are positioned. DEF is a good conductor of electricity. There are 4 rods. 3 of them are used to indicate the fluid level of the tank, the 4th is the ground. The first rod is at the halfway marker. When that rod is submerged, the tank is more than half full. When exposed, the tank is less than half full. And so on to the other two indicator rods. When they are no longer submerged, the PCM can see that by a change in the signal due to the absence of DEF conducting electricity between the level indicator rod and the ground rod. So that's how the hard parts function.

Ok, so let's start with an empty tank. Miles to empty is zero. Now you fill up the tank. The PCM, seeing that the exposed rods are now all submerged, assumes the tank is full and starts with a countdown of miles to empty based on the adaptive learning tables of the DPF system as well as constantly monitoring RPM's, engine load, idle time, etc. Even before the first rod is exposed, the entire time the PCM has been counting down miles to empty. When the first rod is finally exposed, the PCM now knows the correct fluid level, and will re-adjust the miles to empty counter. This will continue to happen as the final two indicators become exposed. It changes because the amount of DEF used will change depending on how the truck is driven, how much it's carrying/pulling, etc.

But let's say we never expose any of the rods and keep them constantly submerged. The miles to empty counter is still running. Continually topping off the DEF and preventing even the first rod from being exposed will not reset or correct the miles to empty counter. The PCM must see a rod exposed and no longer submerged in DEF in order to recalculate the miles to empty.

That is why you never want to continually top off the DEF system. It is important for the level indicators to become exposed so that the PCM can see the correct tank level and re-adjust the miles to empty counter.

Hopefully this helps explain it in more detail.

Unfortunately there isn't much in the Ford workshop manual or the PC/ED manual to diagnose a DEF tank that has been continually topped off, hence why most dealer technicians and service writers are unaware.

 

Yep, that's pretty much the intention.

Which is why it doesn't make sense to create more work to constantly keep the DEF full. Some people believe it's a "piece of mind" thing, but it's not. Just like the OILM. That is designed to alert you to when it's time to change the oil, but with enough oil life to spare so that there isn't any inherent danger of engine damage. Yet some folks still insist on changing their oil every 3,000 miles because of that "piece of mind" feeling. But they aren't gaining anything by doing so, since the oil is still meeting engineering specs of protection. It's just throwing away perfectly good oil.

 

Curtis, thanks for the explanation.
I will admit two things. I usually know about how many miles since I filled Def. There fore I will fill tank if it is under half. If it is convenient.
I don't agree with the statement you make that says it's clearly written in the owners manual. But I will not call you names or show any disrespect.
Again thanks for your interpretation on how the system works.
I enjoy learning how things work. Was a diesel mechanic before I was a Tech.
Listened to quite a few Instructors give the "how it works" explanation in my life. And enjoyed every one of them.

 

Javi, I too interpreted your post as "Tongue in cheek"
And can understand where you were coming from.
I have only seen the Distance to empty message once in my 2012.
Good luck.

 

I get about 4900 miles between def fillups.


But...I also do 5k oil changes. I guess I could do both at the same time but usually I get the def<200 miles while on the road.

 

This is why roadrunner01's idea won't work ie: the pairing fill ups with the IOLM... Maybe if you don't tow heavy but I use more DEF than would work with that plan.

 

Rodney, I agree, that's why I fill when I see below 1/2 when convenient.

 

Adding DEF at oil changes may work, but my truck was below 1/2 at 1200 miles. I assume the factory did not fill the tank when the truck was built. I will just use the message center. Timing it, I would think would not work as at times I tow heavy (11 mpg) at other times I'm solo getting 16-18 mpg's and am using a corresponding amount of DEF is being used. Just my 2 Cents.

(my wife calls in Monkey Pee...I don't disagree)

 

I add DEF whenever the display tells me i'm at 1/2 full level which is about 2.5 gals, I have never let this truck or my 2011 ever get the miles to empty countdown message.

 

I always like it when someone talks to me in a language I understand...'the logic of how it works', 'preciated.

 

Don, you are a lot smoother with words than I am, that's what I meant to say !! LOL