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DEF Capacity & Refill Question


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Had to ad DEF for the first time in my 2018; the 30% warning came up at roughly 4,200 miles. I happened to be pulling into a fuel station soon anyway, so I decided to fill it up as well at 28%. We were out in Montana on a snowmobile trip and I don’t want to run it low with the temps. 

 

This is is probably where I start to over analyze things...

 

Since the DEF tank is 7 gallons; and I was just below 30%, math says I had to add 5 gallons. I bought a pair of the 2.5gal jugs, and got roughly 4gal in before it vomited DEF our the filler hole. It was damn cold and I didn’t have the time or patience to see if I could eek the last gallon or so down.

 

So does the system build up that much air & burp itself, or is the capacity and/or meter off by that much?

 

 

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How cold was it? 

 

DEF fluid freezes around 12f and depending on how I park (truck sloped nose first) and it freezes, next startup I will get a false reading until it thaws out, this is when ithe tank is close to the 30% left, but still reading OK.

 

I know on the 2011-2016 trucks, the system holds more than 5 gallons, but due to the stuff freezing, GM says only 5 gallons due to expansion from freezing.

 

I haven’t looked at the Duramax supplement guide on the 2017+ trucks with the 7 gallon tank, but I am going to assume it is the same. 

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Assuming it was completely full at delivery (zero miles, for easier math) and took 4 gallons at 4200 miles, then  it's getting just about  1050 miles per gallon of def. 

 

So with 3 gallons remaining, it still had 3000 miles til empty.

 

Best to think of it a a DEF 'level indicator' rather than a gauge.  (since it's not very accurate)

 

I don't view the 30% message as a warning. That's just the level that the 'OK message' is no longer displayed and the message displays an 'indication' of how much is left.

 

The first 'warning' is  '1000 mile def range' is reached. 

From 300 mile range and less, it should give an 'xyz range remaining' message at every ignition cycle. 

 

If it gets to 0 remaining, it will then start warnings of distance to escalating speed limitation.

From zero def remaining, another 500 miles til limited to 65 mph

From 65 mph limit another 75 miles to 55 mph

From 55 mph limit another 75 miles to 5 mph limit

 

With 3000 miles til empty and then 500 miles til speed limit -- then there was about 3500 miles til speed limit.

 

 

FWIW, it's not necessary to 'completely fill the def tank each time DEF is added. 

Nothing wrong with just adding a 2.5 jug each time.  

 

When filling and the sound changes, it's time to stop (sorta like sound change when filling fuel).

 

 

Mines a little short of 13,000 miles. Shows 20% on indicator.  

The only time I've added def was about 6500 miles. It had given the 1000 mile warning at about 22%, so a little surprised I haven't seen it yet this time. It gets parked on a slope, sometimes nose up and sometimes down -- maybe that messes with the level indicator.

Planning to wait til 300 miles warning.

 

 

Edited by redwngr
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  • 10 months later...

What is the easiest way to fill the DEF, poor design on GM to have to fill until it overflows, I would think that they have a better way for a $70K truck.

Edited by Lumpy1
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1 hour ago, Lumpy1 said:

What is the easiest way to fill the DEF, poor design on GM to have to fill until it overflows, I would think that they have a better way for a $70K truck.

No need to make it overflow.

 

Stop filling (or pumping if using bulk) when the sound changes as the level gets close to the bottom of the fill tube.  

 

An alternative is to wait until at least the 1000 mile range warning (or the 300) and then just add ONE 2.5 gallon jug. 

Mine usually gives the 1000 mile warning somewhere near 18 to 22% on the def level 'indicator'.

 

Adding til it's at or close to overflow means the jug being used probably isn't empty.

I don't like keeping an open jug around, so I often use the one jug system if I'm not expecting to be near a bulk pump location.  Couple months later - repeat. 

 

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Ok thank you I haven't had to add any yet with just over 3800 miles on it. Dealer topped it off when I bought it.

Dash will occasionally say OK other than that I haven't seen any type of gauge.

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9 hours ago, Lumpy1 said:

Ok thank you I haven't had to add any yet with just over 3800 miles on it. Dealer topped it off when I bought it.

Dash will occasionally say OK other than that I haven't seen any type of gauge.

That is the gauge level indicator .  Imho they shouldn't be called a gauge.

 

When the 'indicator' thinks there is less than 30% of tank capacity left, if will give a % number instead of the 'ok message'.

 

When it thinks you are down to 1000 miles range til empty, the dic will pop a message saying so.  On mine, this occurs somewhere near 20% (+/-).

When it thinks it has 300 miles til empty it will give a DIC message, and it will update the message each time it is restarted. This message will be dismissed.

 

When it thinks it is empty, it will give an empty message and will start and mileage countdown from 500 miles.  This message/display will not clear/cannot be dismissed. 

 

500 miles after empty it is supposed to limit speed to 65 mph for (iirc) 75 miles.

Then xx miles at 55 mph.

Then 5 mph.

 

DEF usage is proportional to fuel usage. 

If towing uses twice as much fuel as not towing then it will also use twice as much def.  

 

 

 

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  • 2 years later...
On 1/5/2020 at 5:46 AM, Lumpy1 said:

What is the easiest way to fill the DEF, poor design on GM to have to fill until it overflows, I would think that they have a better way for a $70K truck.

I agree! The only warning that I receive is a 1,000 miles remaining message I usually pour a 2.5-gallon jug in it at that point, & wait till the next time it gives me the same message & repeat the process. The last time I decided to put two 2.5-gallon jugs in the DEF Tank to so I could fill it more than just partially. I got just shy of finishing the second jug when it puked all over the place, then had to close the filler cap & spray the passenger side of the engine compartment, & front fender down with water to rinse all that crap off of everything. You're exactly right about having some kind of measurement of actually knowing how much DEF is in the tank, or how much to add when it says 1,000 miles left. I can get a better estimate on how much diesel my tank needs to be filled just by the miles since last fill & how many miles per gallon I've averaged. Hell I can get my washer fluid figured out easier without spilling, & don't have to worry about getting that stuff all over my skin or worse yet, in my eyes. I guess we have to spend over $100k before GM will come up with a better design than what they currently have.

 

 

 

 

 

 

 

 

i

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  • 4 weeks later...
On 4/19/2022 at 10:55 PM, Mr. Ruck said:

I agree! The only warning that I receive is a 1,000 miles remaining message I usually pour a 2.5-gallon jug in it at that point, & wait till the next time it gives me the same message & repeat the process. The last time I decided to put two 2.5-gallon jugs in the DEF Tank to so I could fill it more than just partially. I got just shy of finishing the second jug when it puked all over the place, then had to close the filler cap & spray the passenger side of the engine compartment, & front fender down with water to rinse all that crap off of everything. You're exactly right about having some kind of measurement of actually knowing how much DEF is in the tank, or how much to add when it says 1,000 miles left. I can get a better estimate on how much diesel my tank needs to be filled just by the miles since last fill & how many miles per gallon I've averaged. Hell I can get my washer fluid figured out easier without spilling, & don't have to worry about getting that stuff all over my skin or worse yet, in my eyes. I guess we have to spend over $100k before GM will come up with a better design than what they currently have.

 

 

You should get warnings at each start-up once it gets to 300 miles til empty.

 

When it gets to empty it will start a 500 mile countdown to the first (65 mph) speed limit. 

 

It should be using about 2% of fuel.  So 125 gallons of fuel should use 2.5 gal def.

(125 x 0.02 - 2.5 gal)

 

What year is your truck?

LML had a 5.3 gal tank.

L5P went to 7.0 gal..

 

 

Edited by redwngr
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