3.0L Duramax - who owns or has driven one

tayhadagti · June 9, 2020

Anyone experience using like no DEF? I have 1,700 miles on my 3.0 and my def is still 100% full according to the gauge.

burninoil · June 9, 2020

mine is at 3000 miles an is at half , no idea if it was completely full when I picked truck up but it did show full. if you don`t tow with your truck it won`t use much.

Jav_eee · June 9, 2020

Not sure if these truck has an actual float but fords (2011-2016 at least) have level sensors. They show full, half, and low. No in between.

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burninoil · June 9, 2020

its gradual or at least mine is.

ullose272 · June 10, 2020

I have about 3000 miles and just over 1/2 tank

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topgear1224 · June 11, 2020

Anyone experience using like no DEF? I have 1,700 miles on my 3.0 and my def is still 100% full according to the gauge.

Some of the trucks have "bad" gauges and it will suddenly plummet to half.

I've noticed that it's more RPM dependent then load (although the metric is DEF per gallon of fuel used) for instance when I have it in off-road mode and I'm running the dirt roads a lot with rail to the high RPM going up the hills it will say it's using a ton of d e f I'll know on the next fill-up what my actual average is since I only put in 5 gallons.

Mine was completely empty at 2771.

4646 now and it's over half full.

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jnissen · June 11, 2020

Mine showed half full when I picked it up off dealer lot. If I had noticed I would have insisted it was full. I put in 2.5 gallons at about the 600 mile mark and it shows full and hasn’t really moved at all in a couple hundred highway miles.

BJ Niceguy · June 12, 2020

take this for what it is worth. When towing, mine uses a bunch of def compared to normal driving which makes sense. I drove 2500 miles not towing and gauge showed 1 bar above half. I towed about 400 mils and alert came on saying out of def. Refilled and it took 4.3 gallons. I bought a plug in scanner. It appears that the bar gauge shows full from 100% down to about 80% before moves. I have put in 2.5 gallon box and raised from 40% on scanner (50% on bar gauge) to 80% on scanner (full on bar gauge). On the scanner when gets down to 35-40% my bar gauge drops instantly from 1 bar below half to alarm. Not impressed at all with the gauge. My real concern is when towing being able to get full 2.5 gallon box in without getting so low I get alarm. Mine appears to use 1/2 gallon per hundred miles when towing hard (altitude, strong head winds, high speed) where engine runs 2500 rpm range. It appears to use 1/3 gallon per hundred miles when can hold mostly 1,700 RPM in 9th gear. Very little usage if driving without towing.

I took truck back to dealer. They let me set for couple hours, came out and said nothing wrong, and gave me a nice 5 page letter explaining that vehicle will use def if towing and a single sentence saying the gauge is not a normal float gauge. No further explanation as to how gauge works, just have a nice day. That is when I bought the scanner for phone recommended by others on this site. It is nice to see stuff, but really not necessary.

topgear1224 · June 12, 2020

take this for what it is worth. When towing, mine uses a bunch of def compared to normal driving which makes sense. I drove 2500 miles not towing and gauge showed 1 bar above half. I towed about 400 mils and alert came on saying out of def. Refilled and it took 4.3 gallons. I bought a plug in scanner. It appears that the bar gauge shows full from 100% down to about 80% before moves. I have put in 2.5 gallon box and raised from 40% on scanner (50% on bar gauge) to 80% on scanner (full on bar gauge). On the scanner when gets down to 35-40% my bar gauge drops instantly from 1 bar below half to alarm. Not impressed at all with the gauge. My real concern is when towing being able to get full 2.5 gallon box in without getting so low I get alarm. Mine appears to use 1/2 gallon per hundred miles when towing hard (altitude, strong head winds, high speed) where engine runs 2500 rpm range. It appears to use 1/3 gallon per hundred miles when can hold mostly 1,700 RPM in 9th gear. Very little usage if driving without towing.

I took truck back to dealer. They let me set for couple hours, came out and said nothing wrong, and gave me a nice 5 page letter explaining that vehicle will use def if towing and a single sentence saying the gauge is not a normal float gauge. No further explanation as to how gauge works, just have a nice day. That is when I bought the scanner for phone recommended by others on this site. It is nice to see stuff, but really not necessary.

Yeah it's kind of like fuel gauges. on my 2001 2500HD E means EMPTY!! You about to run out of fuel in 5 to 10 miles!! (Done it twice while towing HEAVY)

on this new truck the fuel light doesn't even come on until the gauge is basically sitting on E.

I feel like they did the same thing with the DEF gauge. It'll say 1000 miles remaining but then if you go and hook up your trailer and pound on the truck you'll blow through that 1k miles in 150miles. It's trying to predict future usage based on short-term usage and it's really not good at it.

the metric is supposed to be DEF per gallon of fuel used. GM really should have just threw that stupid bar graph away, and given us a consumption gauge like they do for fuel but instead change it to DEF and allow us to set it for the last 25 miles, last 50 miles, or the last hundred miles. Deep down inside the ECM it knows exactly how much "reagent" it's injecting.

They could have given us an estimated range for the DEF remaining on that same screen.

now to be fair if I lived somewhere with DEF at the fuel pump I would just fill up every other fill up and not worry about it. (I avg about 1k-1.5k/month)

But since I have to buy it in bottles from Walmart that means I have to wait until I know I can get all 5 gallons in it because I'm not going to roll around and risk it leaking inside of my cab.

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steve841 · June 12, 2020

You guys dont know how good we have it now ....

My first diesel was the 6.6 in my 2500 and the DEF tank was under the hood and NO gauge at all.

The only time you knew to fill the tank was when you got the 55mph max warning on the DIC.

Edited June 12, 2020 by steve841

BJ Niceguy · June 12, 2020

I agree that I would be happy if the gauge was just reasonable about when have room for 2.5 gallons. Unless it did calculations based on average mileage for last 25 miles versus the remaining in tank to continually refigure remaining mileage, don't see how it can guess on long term remaining (like 1,000 miles). I filled this morning, the scanner said 45% and the bar gauge said 2 bars from full which I would read as between 65% & 75%. It took 3.1 gallons which is close enough with the scanner ( 5.3 gallons times 55% used = 2.95 gallon) to avoid ever getting the alarm. I am not sure it will allow you to ever get low enough to put in 5 gallons without throwing a bunch of alerts.

topgear1224 · June 12, 2020

I agree that I would be happy if the gauge was just reasonable about when have room for 2.5 gallons. Unless it did calculations based on average mileage for last 25 miles versus the remaining in tank to continually refigure remaining mileage, don't see how it can guess on long term remaining (like 1,000 miles). I filled this morning, the scanner said 45% and the bar gauge said 2 bars from full which I would read as between 65% & 75%. It took 3.1 gallons which is close enough with the scanner ( 5.3 gallons times 55% used = 2.95 gallon) to avoid ever getting the alarm. I am not sure it will allow you to ever get low enough to put in 5 gallons without throwing a bunch of alerts.

It does if you just drive it to where the bar actually goes red. On my last fill up I think it said that I was like ten miles to speed limited.

It doesn't hurt anything, you're not producing any extra emissions until it actually runs out of DEF.

when you get the undismissable reminder that's when you can fit about 5 gallons in.

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BJ Niceguy · June 12, 2020

the first times I got that undismissable alarm, mine took 4.2 gallons at pump (dropped from 1 bar under half to that alarm in 75 miles going thru what I call 1st alarm). Second time it took 3.8 gallons. I only drove 20 miles each time after that out of the 500 miles it said I had before speed limiting. I think they did something when the dealer had it cause it seems to use less def this last towing trip and I got down to 2 bars under half before jumped to 1st alarm. Scanner was at 35% I think.

topgear1224 · June 12, 2020

the first times I got that undismissable alarm, mine took 4.2 gallons at pump (dropped from 1 bar under half to that alarm in 75 miles going thru what I call 1st alarm). Second time it took 3.8 gallons. I only drove 20 miles each time after that out of the 500 miles it said I had before speed limiting. I think they did something when the dealer had it cause it seems to use less def this last towing trip and I got down to 2 bars under half before jumped to 1st alarm. Scanner was at 35% I think.

So one thing that I knew of but I haven't really talked about is the ECM has the ability to monitor frictional losses inside the engine.

For instance my oil temperatures were alarmingly high (330°+) when I first got the truck, they have since settled way down and I believe that was due to increased friction from the break in process.

to the best of my knowledge, those same increased frictional losses would cause increased fuel consumption or at least the higher oil temperatures would lead me to believe that the in cylinder temperatures are increased which requires more DEF to be used, since high temperatures create more NoX, DEF controls nox output.

This is just a guess, an educated guess, but a guess nevertheless.

I'm now approaching 5,000 miles and it still says I have over half a tank remaining.

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Firetrout · June 12, 2020

Like those above, when towing it seems to use much more, which is expected. Bar graph is pretty much just a useless visual for me, seems spastic in its reading once it comes off full, especially when towing. On another note, going in for oil and fuel filter change this week. Just turned 20k miles on it and all is going well. Of the 20k miles about 1.8k is towing and rest is mostly highway. I have a 175 mile commute each way, once a week.