3.0 Duramax DEF consumption

topgear1224 · June 22, 2020

I get its a "range gauge" but what I don't get why it would be down two bars for a month and then jump to full

More highway use?

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BurnsMax · June 22, 2020

Mostly city driving

BJ Niceguy · June 23, 2020

I have a diagnostic scanner thingy with phone app LOL. I have done mostly towing after break in, so have gone thru a lot of def. The scanner has a digital gauge and the truck bar graph and it are not consistant to each other nor do they repeat real close. So far the 1st bar of the gauge drops out between 80% & 85% on digital gauge. The second bar so far has dropped at 70% to 75%. From there not a lot of consistancy. When my gauge hits half to one bar above half, the digital is at around 45% to 50%. The digital bounces around a lot more as tank goes down so I assume the fluid slops around more. I have put in a 2.5 gallon box at 45% 2 times and both times the digital came up to 85% to 90% and bar gauge went to full.

If I let the digital gauge get down to about 35% my bar gauge went to red with alarm. My bar gauge drops from 1 bar below half to alarm VERY quickly. Obviously if you are not towing, the def lasts forever. Towing it seems to go down quickly. I tow 4500 lb enclosed trailer and there is a big difference in usage if fighting wind and getting 12.5MPG or going good getting 14.5MPG. Not quite double, but close.

This is what I have observed and you may see similar or totally different results depending on your load, speed, wind or how heavy a foot you have LOL

BurnsMax · June 23, 2020

Yeah I will have to get my scanner out and check it on there because today it is now showing half full on the DEF gauge. Guess it can't make up its mind on what level it wants to read at.

ullose272 · June 23, 2020

Just topped mine off 3.5 gallons at 3200 miles

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BurnsMax · June 23, 2020

Well I had to call the dealer about warranty work and there happens to be a recall on the DEF system. He didn't have all the details on what it was. I guess I will find out when I take it in on the first.

Robert Oehmke · June 24, 2020

I have a 2020 Sierra 1500 AT4 with the 3.0 Duramax. I just got back from a 2500 mile trip pulling my 27" RV about 6500 lbs. I used 15 gallons of DEF. This seems a lot! the pictue below with miles at 4116 the DEF was Full. At 4475 miles I was almost out. I took my truck to my local GMC Dealership when I got back. They can't seem to find anything wrong with the engine. Does anybody have similar issues? Is this normal? Thank You..

Edited June 24, 2020 by Robert Oehmke

topgear1224 · June 24, 2020

I have a 2020 Sierra 1500 AT4 with the 3.0 Duramax. I just got back from a 2500 mile trip pulling my 27" RV about 6500 lbs. I used 15 gallons of DEF. This seems a lot! the pictue below with miles at 4116 the DEF was Full. At 4475 miles I was almost out. I took my truck to my local GMC Dealership when I got back. They can't seem to find anything wrong with the engine. Does anybody have similar issues? Is this normal? Thank You..

You used a full tank and a half in 2,500 miles???

How much fuel consumed?

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LaRed · June 24, 2020

I took mine in for excessive use of DEF. My post is on earlier on this thread for details. Chevy said they reprogramed to hopefully improve but gave me a written explanation telling me to expect high usage while towing. I was back at the dealer today (my truck lurches into gear upon restart after sitting at a light. Im told this is a 2 day fix after waiting almost 3 months for the part) and they asked if my DEF usage has improved under load. I can't answer because I have not had an occasion to tow anything more than a few miles. Apparently,, now there is a recall notice for excessive DEF usage with the 3.0 Duramax.

I hope this greatly improves because it is definitely excessive while towing. I don't think I should be expected to load up 7 1/2 gallons of DEF in the bed for a 1500mi round trip while pulling a 3957lb (I know cause I weighed it) boat, motor, trailer loaded with fishing gear.

I really like this truck but this issue adds another headache and makes it a poor cost, benefit relationship.

This will not be a long term marriage if this is normal.

topgear1224 · June 25, 2020

I took mine in for excessive use of DEF. My post is on earlier on this thread for details. Chevy said they reprogramed to hopefully improve but gave me a written explanation telling me to expect high usage while towing. ....

I hope this greatly improves because it is definitely excessive while towing. I don't think I should be expected to load up 7 1/2 gallons of DEF in the bed for a 1500mi round trip while pulling a 3957lb (I know cause I weighed it) boat, motor, trailer loaded with fishing gear.
I really like this truck but this issue adds another headache and makes it a poor cost, benefit relationship.
This will not be a long term marriage if this is normal.

It isn't normal.

So with GM betting so hard on the LM2 they're trying not to get hung up like Chrysler did with their EcoDiesel for emissions. There's no doubt in my mind that they are over treating this exhaust system. Overtreatment doesn't cause an increase in emissions unlike for instance over or under fueling.

What I've noticed is even though your fuel usage doesn't increase if you run higher RPMs (with the same load) it starts to really drink Def. For instance is a dirt road that's 500 miles long approximately 375mi is dirt. I run off road mode on the dirt sections. Round trip it definitely consumes more def than normal and I can verify that with the scan gauge. I run off road mode to stop it from upshifting to 1100 RPM where I'm definitely getting some rattling I believe it's the vgt linkage but it's causing vibrations in the actual power train (power pulses) which makes me worry it may be related to the timing chains.

Even with low oil temps (160-180) I'm still seeing higher usage. Oil temps is a good indicator of cylinder heat. I also look at the egts and they tend to stay around 600 or so. burning lean creates nox.

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topgear1224 · June 25, 2020

I was back at the dealer today (my truck lurches into gear upon restart after sitting at a light. Im told this is a 2 day fix after waiting almost 3 months for the part) and they asked if my DEF usage has improved under load.

Can you please post what they did.

I have the same issue, dealer told me either push the brake to the floor to force it to restart with the brakes still applied or turn the system off.

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redwngr · June 25, 2020

7 hours ago, LaRed said:

I took mine in for excessive use of DEF. My post is on earlier on this thread for details. Chevy said they reprogramed to hopefully improve but gave me a written explanation telling me to expect high usage while towing. I was back at the dealer today (my truck lurches into gear upon restart after sitting at a light. Im told this is a 2 day fix after waiting almost 3 months for the part) and they asked if my DEF usage has improved under load. I can't answer because I have not had an occasion to tow anything more than a few miles. Apparently,, now there is a recall notice for excessive DEF usage with the 3.0 Duramax.

I hope this greatly improves because it is definitely excessive while towing. I don't think I should be expected to load up 7 1/2 gallons of DEF in the bed for a 1500mi round trip while pulling a 3957lb (I know cause I weighed it) boat, motor, trailer loaded with fishing gear.

I really like this truck but this issue adds another headache and makes it a poor cost, benefit relationship.

This will not be a long term marriage if this is normal.

Sounds like it might be overusing, but even if it is, why would you haul def in the bed?

It's available anyplace you can buy fuel and also at any autoparts store or department store with an auto section.

steve841 · June 25, 2020

Could anyone who had the recall done please post that portion of your work order?

LaRed · June 26, 2020

22 hours ago, redwngr said:

Sounds like it might be overusing, but even if it is, why would you haul def in the bed?

It's available anyplace you can buy fuel and also at any autoparts store or department store with an auto section.

Because I don't want the inconvenience of stoping/hunting for a place to buy it and sorting through a pile of boxes to be sure I buy DEF that is in date. Other than that I guess you're correct..

BJ Niceguy · June 26, 2020

most large truck stops have it set up at pump. ($2.99 gallon in our region) I built a rack in my enclosed trailer to hold 2 boxes. Keep it in house where cool till get ready to go (lasts longer in cool areas). It is more of a nuisance than a problem, but I do think uses too much.