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-   -   Ok to top off DEF tank? (

navybanker 08-11-2019 01:12 PM

Ok to top off DEF tank?
For some forgotten reason, have a hand written note in the diesel manual for my truck saying do not top off DEF before the 999 mile before reduced speed warning on the DIC. Leaving on a long trip with Montana and thinking of adding DEF before we leave. Know to be careful and not allow overflow! Yes, I wrote the note several years ago but not sure why! Manual and internet search didn't find anything. Thanks,

Daryles 08-11-2019 01:41 PM

We were coming home to Mo. from SD when I got the 500 mile DEF warning 2016 F350. No problem, we will be home before then (about 300 miles to home). However when towing it appears you use more than you think. We ran out about 30 miles from home. Got a new warning, speed will be reduced if we do not fill up within 50 miles.
Stopped at the next gas station and bought a 2 gal refill. After we got home I topped it off. And yes I over filled it and it ran out the fill cap. I just washed it off.

Carl n Susan 08-11-2019 02:34 PM

My Ford tells you the level is OK, below 1/2, or you have 500 miles to go. You do not want to run out of DEF. I check the level each day when driving. When it says it is below 1/2 full, I wait 100 miles (1/2 empty is not really 1/2 empty) and then top it off. This has worked great for 100K+ miles.

You can buy a DEF fill nozzle from Ford, but much cheaper on Amazon, that doesn't spill DEF if the tank fills up before all of the 2 1/2 jug is gone.

1retired06 08-11-2019 03:49 PM

No problem topping off your DEF tank.

MidMOTraveler 08-11-2019 04:14 PM

Top off at truck stops don’t mess with jugs .

rames14 08-11-2019 04:20 PM

I like to keep it above half way. I also fill at truck stops, but this past winter our DEF froze up coming back from Quartzite (-13) in Wyoming. The service tech said they have found water in some of the DEF from the pump. From now on, especially in cold weather, I will use the jugs.

Mikendebbie 08-11-2019 07:47 PM

My 2014 Chevy used to show a warning something like “DEF level low 989 miles”...I don’t remember exactly but it was always in the 900 mile warning. The new Chevy pops up in the 400 to 500 mile range. For the 2014 I remember the dealer told me to add a 2.5 gal jug...I took that to mean “only one jug”.For the 2019 same dealership said I could add 2 jugs (5gals) each time the warning goes off. Chevy does not have a gauge -it’s either ok or it needs DEF.

mjammersc 08-12-2019 08:38 AM

My understanding is that this is just based on a desire to have the DEF as fresh as possible. If you wait til you get the warning, it'll be mostly newDEF in the tank. I have a Chevy Duramax and add a 2.5 gallon jug the next chance I get after the warning. Its usually good for another couple thousand miles then, even towing.

MidMOTraveler 08-12-2019 08:58 AM

DEF is 67% Deionized Water !
Yep I’ll bet that tech found water in it ��

jeffba 08-12-2019 09:21 AM


Originally Posted by MidMOTraveler (Post 1155331)
DEF is 67% Deionized Water !
Yep I’ll bet that tech found water in it ��


I blow through about 2.5 gal of DEF per 1000 miles when towing.
Ford finally added a gauge. Of couorse it takes forever to move off of F then runs down rather quickly

Skw774 08-12-2019 10:22 AM

It is o.k to add anytime you want/need too. Or if you can delete that mess,no more def.

artfuldodger 08-12-2019 01:22 PM

Yes DEF is 67 per cent water and it freezes around 16 deg. F. If your tank is full it could rupture during cold weather. Always, in cold temps fill to about 80 per cent.

MidMOTraveler 08-12-2019 01:41 PM

Can’t say about other brands but Ford has a heater in the DEF tank.
I do store my Ford for the winter and do leave the DEF tank less than full.

RoadRunnerTR21 08-12-2019 01:43 PM

Yes, you may top off your DEF tank. Just be careful in the winter

Slufoot733 08-12-2019 02:45 PM

A note of caution. I buy DEF in the jugs. A buddy did the same but fund that someone had poured out the DEF and replaced it with plain tap water, then returned the jug to the store. Now when I buy DEF in a jug I always remove the cap and check the seal to be sure someone didn't mess with it.
As for topping problem. Just do NOT run out. Those darn computer know when you do and they cannot be reasoned with! ;)

mazboy 08-12-2019 05:17 PM

Keep your def fresh.

Any left over in a container not keep.

Mikendebbie 08-12-2019 05:51 PM

DEF tank heaters
Chevys definitely have a tank heater. The heater in my 2014 went out at just over 100k miles. They do not replace the heater- they replace the whole tank.
But good info about not filling the tank too full during cold weather. Makes sense.

mlh 08-12-2019 06:01 PM

Since you never fully empty the tank you always top it off.

Theunz 08-12-2019 08:26 PM


Originally Posted by mazboy (Post 1155398)
Keep your def fresh.

Any left over in a container not keep.

Curious, what would be the difference between storing it in the trucks tank vs in the jug it came in?

artfuldodger 08-13-2019 09:45 AM

Yes there is a heater in the def tank. I had to change mine (ford) after it stopped working. It of course only works when the vehicle is running so a totally full tank will freeze solid at very cold temps. below 16F and split the tank. Also, a container of def will freeze and could split. If it is frozen it is unusable( won't pour) until it is thawed out. By the way, Ford has an extended warranty on that def heater and I was reimbursed by them a year later, when it was announced.

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