DEF usage. 6.6 vs 3.0

topgear1224 · April 17, 2020

How much def do the big diesels use?

dealer told me I should be able to go at least 10k miles on the 5 gallon tank(distance of an oil change) in my 1500 LM2. I am under 2500 and it says 200miles left. Truck has 40.8 idle house (37 from the dealership) had 3/4 tank DEF when I bought it.

DEF is 15.28/gal or 26.55/2.5gal up here. Plus labor( service advisor wasn't able to tell me if they could charge just half an hour of labor or if they have to charge a full hour)

Only way to have DEF failures covered by GM under warranty is to have Dealer fill it. I looked at some TSB documents that basically say DEF contamination is the owners problem. service advisor agreed that unless the dealer was actually filling it up and you have documentation for it that GM is just going to leave you out on your own.

hes had 2 L5P come in on their first fill up they used super tech and it was contaminated and he said the repair was $6,000 on each customer. GM refused to assist.

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Colossus · April 18, 2020

Don't believe the dealer. They only know how to sell trucks, and even that can be questioned.

topgear1224 · April 18, 2020

Don't believe the dealer. They only know how to sell trucks, and even that can be questioned.

All I know is next closest GM dealer is 6 hours away each way and local dealer is stingy as hell.

Lifetime average is 24 MPG. So 101 gallons of fuel used. 5.5 gallons of DEF used in that time seams high.

18.36 gallons of fuel per 1 gallon of DEF.....

You HD guys really filling up with 7 gallons of DEF every three tanks when driving unloaded??

dealer is basically saying that if they can't prove that they put it in there GM is going to claim that there was contamination and that's what caused the failure.

Apparently GM also has a memo stating only genuine ACDelco DEF is authorized for Duramax?? And if I use something else, the warranty on the whole emission system is void? they are trying to say it's like if I went and filled up my truck with gasoline instead of diesel.

Bulletin No.: 19-NA-237

"This bulletin is being published to help technicians identify signs of contamination in Diesel Exhaust Fluid (DEF). If you see evidence of contamination take appropriate measures to ensure that all of the contaminated fluid is removed from the vehicle. Any components that have failed as a result of contamination should NOT be covered by warranty"

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redwngr · April 18, 2020

6.6L uses 'about' 2 gallons of DEF per 100 gallons of fuel.

(GM docs published when when def first put into use suggested about 1.75%,. This jives with the mileage I've been getting, but 2 is a good number for estimating.)

When it works harder and uses more fuel, it will use more DEF as well.

DEF screen is better called and 'indicator' than a 'gauge' .

If you really want to know how much it's using fill the tank, drive 3 or 4 or 5000 miles and fill it again to see how much it used.

Both my 6.6L trucks have run about 1100 to 1200 miles per def gallon.

3.0 should use less fuel, so I'd expect def economy to also be better.

topgear1224 · April 18, 2020

6.6L uses 'about' 2 gallons of DEF per 100 gallons of fuel.

(GM docs published when when def first put into use suggested about 1.75%,. This jives with the mileage I've been getting, but 2 is a good number for estimating.)

When it works harder and uses more fuel, it will use more DEF as well.

DEF screen is better called and 'indicator' than a 'gauge' .
If you really want to know how much it's using fill the tank, drive 3 or 4 or 5000 miles and fill it again to see how much it used.

Both my 6.6L trucks have run about 1100 to 1200 miles per def gallon.
3.0 should use less fuel, so I'd expect def economy to also be better.

Hold crap so I do have a problem then.

Lifetime economy from 21 miles is 24mpg.

101 gallons of fuel used.

The tank is empty 100 miles to speed limit.

So my truck used 2.25 times what the 6.6 uses. WOW

Any links that documentation so I can show the dealer.

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migrabill · April 18, 2020

Keep in mind - GM is shipping trucks to the dealerships with only half a tank of DEF. so you started off with only half a tank.

redwngr · April 18, 2020

25 minutes ago, topgear1224 said:

Hold crap so I do have a problem then.

Lifetime economy from 21 miles is 24mpg.

101 gallons of fuel used.

The tank is empty 100 miles to speed limit.

So my truck used 2.25 times what the 6.6 uses. WOW

Any links that documentation so I can show the dealer.

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GM does not fill the def tank (or the fuel tank) at the factory.

In the 6,6 world it has always been an issue that dealers also don't fill it prior to delivery.

I'd bet yours wasn't filled either.

When the the first low def warning happens -- it's easy to assumes the tank was full (and/or the gauge was accurate) at delivery.

Yes, there are 6.6 trucks that are reporting using too much def. Presumably there will be 3.0's that use to much as well.

Not being filled initially, and the long time / many miles it takes to run out a tank of def makes it difficult to get a good calculation.

You should be able to buy DEF for$10 or $12 per 2.5 gal (10L) . (bulk DEF is about C$0.89L in sw ont at truckstop)

All DEF is made to the same ISO spec number and it has no additives.

Get whatever brand you like from a source that moves alot so it is fresh. (or fill it the truck with a bulk hose at a truckstop)

I'd fill it to the top and then run it til it gives the next low def warning then refill and calculate the def mpg over that interval.

topgear1224 · April 18, 2020

GM does not fill the def tank (or the fuel tank) at the factory.
In the 6,6 world it has always been an issue that dealers also don't fill it prior to delivery.
I'd bet yours wasn't filled either.

When the the first low def warning happens -- it's easy to assumes the tank was full (and/or the gauge was accurate) at delivery.
Yes, there are 6.6 trucks that are reporting using too much def. Presumably there will be 3.0's that use to much as well.

Not being filled initially, and the long time / many miles it takes to run out a tank of def makes it difficult to get a good calculation.

You should be able to buy DEF for$10 or $12 per 2.5 gal (10L) . (bulk DEF is about C$0.89L in sw ont at truckstop)
All DEF is made to the same ISO spec number and it has no additives.
Get whatever brand you like from a source that moves alot so it is fresh. (or fill it the truck with a bulk hose at a truckstop)

I'd fill it to the top and then run it til it gives the next low def warning then refill and calculate the def mpg over that interval.

I believe the dealer originally filled the tank but it had 21 miles and 33 idle hours on it. Now has 41 idle.

Gage was over 3/4. (They said it reads low when cold.... Obv know now they were lying)

Just broke 100 total engine hours.

The build date on the bumper indicates that it's 11 months old.

is it possible to truck knows how long the DEF is been in there so now it just started to guzzle it all?? It used half a tank in 600 miles.

2.5 gallons is $26.55 here. I could get the super tech stuff but every single bottle at Walmart is leaking from them being frozen at -40.

that in the dealer literally saying if I don't use ACDelco they're going to submit it as a DEF fluid problem when it cracks the lines this winter. (Apparently the tank does not like -40c)

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newdude · April 18, 2020

On 4/17/2020 at 4:48 PM, topgear1224 said:

How much def do the big diesels use?

dealer told me I should be able to go at least 10k miles on the 5 gallon tank(distance of an oil change) in my 1500 LM2. I am under 2500 and it says 200miles left. Truck has 40.8 idle house (37 from the dealership) had 3/4 tank DEF when I bought it.

DEF is 15.28/gal or 26.55/2.5gal up here. Plus labor( service advisor wasn't able to tell me if they could charge just half an hour of labor or if they have to charge a full hour)

Only way to have DEF failures covered by GM under warranty is to have Dealer fill it. I looked at some TSB documents that basically say DEF contamination is the owners problem. service advisor agreed that unless the dealer was actually filling it up and you have documentation for it that GM is just going to leave you out on your own.

hes had 2 L5P come in on their first fill up they used super tech and it was contaminated and he said the repair was $6,000 on each customer. GM refused to assist.

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It sounds like you might not have gotten a full tank at delivery? The 2020 trucks do use a bit more DEF than the old ones however. See below:

Quote

#20-NA-082: Information on Excessive Diesel Exhaust Fluid (DEF) Usage - (Apr 7, 2020)

Some customers may comment that excessive DEF is being used.

Some technicians may find no codes set or messages on the DIC.

The current 2020 Silverado/Sierra is the first to have a DEF level gauge on the IP. This is the first time a customer can see a representation of how much DEF is in the tank up to the full capacity of the tank. This gauge does not operate like the float style gauge that you have in your fuel tank. Because of this, you may see some fluctuation in the gauge. It may also take a few key cycles to register the correct amount in the tank after a fill event. With the new segmented DEF level gauge, it is possible that after adding 5 gallons (18.9 L) of DEF that the gauge reads as a full tank after the fill event. However, if the actual level of DEF is just entering the last segment on the gauge, the gauge is likely to drop by one segment shortly after driving after the fill event. This could give an initial impression that the vehicle consumes a lot of DEF.

Every year that GM produces vehicles with diesel engines, the requirements to reduce Nitrogen Oxides (NOx) in the vehicle exhaust continue to get more aggressive. Because DEF is required to reduce the NOx in the exhaust, DEF consumption will increase as NOx reduction requirements increase. When customers trade in an older model year diesel Silverado/Sierra for a newer model year, there will likely be an increase in DEF usage. DEF consumption increases as the newer vehicles meet the more stringent emission requirements for that model year.

The amount of DEF usage is also a function of how hard the engine is working, or engine load. Because of this, it is more representative to compare DEF usage to the amount of fuel used, also a function of engine load, instead of miles traveled. In addition to engine load, other factors that affect the DEF usage rate are the humidity, temperature, and altitude where the vehicle is operating.

Under certain conditions, the ECM will increase or decrease the amount of DEF used based on learning or adaptive algorithms. In the event of a malfunction and SES light, the ECM may double or even eliminate the amount of DEF that is being used. This will continue until the vehicle is repaired and until the learned value in the ECM is reset.

topgear1224 · April 18, 2020

I feel like $50 bucks in DEF for every $270 (100 gallons) of fuel is a bit crazy.

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newdude · April 18, 2020

1 minute ago, topgear1224 said:

I feel like $50 bucks in DEF for every $270 (100 gallons) of fuel is a bit crazy.

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Sure at GM pricing. You can buy good quality DEF for much less at plenty of places.

topgear1224 · April 18, 2020

Sure at GM pricing. You can buy good quality DEF for much less at plenty of places.

dealer is saying that WHEN I have a DEF issue, which every single one of their Duramax up here in this weather eventually does (of course they didn't mention this to me BEFORE I bought it), they will not cover it unless I can prove that I only used ACDelco fluid installed by them.

Now normally I would just be like yeah whatever.....

But the kind of DEF failure that's occurring up here is related to condensation based contamination. GM's DEF bulletin explicitly states that contamination based failures will not be covered under warranty. It is up to the dealer to assess whether or not contamination occurred or not.

I probably covered in another thread but basically what's happening is we have a condensation issue that occurs because it'll be negative 40 degrees outside and then 70 degrees inside of your garage. When you bring the truck on all the ice melts and it turns into a huge sauna. This leads to water buildup in your fuel system (both gas and diesel) which means every fill-up you have to use a bottle of HEET. Apparently according to the Master tech at the dealer. (Seams much more knowledgeable then most "master" tech I meet who can't even explain flame fronts.....)

One of the big issues he is seeing is that condensation buildup is building up inside the DEF tank. And since the DEF system shuts down once the fluid in the tank freezes, for eight months out of the year the truck does not use any DEF (it'll use a little bit when you back out of the garage but once the ambient sensor falls below the threshold the system will shut off) but it continues to take on more and more water vapor. This leads to water contaminated DEF fluid. our first warm up of the year when the system finally turns itself back on, usually the following day we get a hard freeze. during the hard freeze all that water contaminated DEF breaks everything from the pump to the lines to literally splitting the injector.

at that point it becomes a judgment call. because according to GM any contamination to DEF is the customers problem and will not be covered in any way shape or form by general motors.

now for years the dealership has just replaced the system's knowing that they just can't cope with the weather that we have here. But last year two particular brand new 2020 L5P trucks had a massive DEF failures. GM flagged the warranty repair and told the dealer that they had to prove that the customer used genuine AC Delco fluid in order for them to authorize the warranty repair as a courtesy.

Since they used Supertech GM told the dealer to have the customer reach out to Supertech to get them to fund the repair. Both customers ended up trading in the trucks over the 6k repair bill.

there isn't really a way around this sure you could top the tank off but then your tanks going to split when the DEF fluid freezes. (Ironically also explicitly called out for a non warrantable repair)

Now why is AC Delco fluid the solution I asked him. And it's because it's a unique clause because general motors considers AC Delco products genuine replacements. They come with a parts warranty, this warranty also extends to the fluids.

this means that it is basically impossible for general motors to deny the claim because even if general motors does. the client may can go through AC Delcos warranty system for their product to cover the repair. the only caveat is ALL DEF filling MUST be done with a service ticket to prove that it was done by a qualified trained general motors technician.

This way you have three safety nets in place. you have the AC Delco parts warranty, you have the fact that you used a genuine parts so therefore it should be covered under any repair that it causes from general motors, and you had the dealership perform the work which then their work is also covered.

Now I could just roll the dice as there's no particular part of DEF system that's necessarily hard to replace. but he has had one failure where the injector split in such a way that the system just pumped out all of the DEF in the tank into the DPF and ruined it.

now normally I would just say screw it and find another dealer but the next nearest dealer is 6 hours away each way and it's pretty hard to justify an 800 mile round trip especially if you have the speed limited warning from a failure.

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topgear1224 · April 18, 2020

18.2 gallons of fuel per gallon of DEF is on another level.

dealer is no help they said just live with it until it throws a code.

same way they told me just drive my truck and brake harder until GM releases a calibration for the fact that I have no brakes until the final quarter of the pedal travel.

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mookdoc6 · April 18, 2020

Wonder why the DEF tanks keep getting bigger? Wonder why more people go from Diesel to Gas? Wonder why FERD has a 7.3L gasser now? Wonder why GM has not released it's Big Block/Big Bore...not sure about that rumor has it's coming. They all spend hugely to make Diesel compliant course the new L5P sucks more DEF much more........Are you towing for a living? Get a gasser is all I can say. Relieve yourself of 40 GM Hoops to maintain valid warranty and writing novels on figuring out the IN/OUTS. Why even mess around with Diesel at -40 it's always going to cost WAY MORE THAN IT'S WORTH

topgear1224 · April 19, 2020

3 minutes ago, mookdoc6 said:

Wonder why the DEF tanks keep getting bigger? Wonder why more people go from Diesel to Gas? Wonder why FERD has a 7.3L gasser now? Wonder why GM has not released it's Big Block/Big Bore...not sure about that rumor has it's coming. They all spend hugely to make Diesel compliant course the new L5P sucks more DEF much more........Are you towing for a living? Get a gasser is all I can say. Relieve yourself of 40 GM Hoops to maintain valid warranty and writing novels on figuring out the IN/OUTS. Why even mess around with Diesel at -40 it's always going to cost WAY MORE THAN IT'S WORTH

i do 20K a year. originally got the 5.3, falls flat on face at high RPM. did a swap only option was 3.0, no 6.2 on lot.

2019 5.3 had a ton of other electrical issues. was avg 20 MPG highway at 55. drove a few all were lazy on highway. lazy is okay if MPG backs it up. 20mpg is only 6 better than my 2003 2500HD 8.1.

3.0 gets 33mpg same highway same speed. needed 5yr 100K warranty to back up 5yr loan. made sense.

5.5 DEF tank SUPPOSED to last for a full oil change cycle (approx 10K miles) . didn't know about the d-max issues up here. NOR about the Supertech issue.

me from another thread

"I have 2400 miles and showing 180miles remaining...... Def is 15.28/ GALLON up here.......

That's .04/mile in DEF. Or based on my 24mpg avg and extra 0.96 per gallon of fuel used.....

Diesel is $2.70 +$0.96 in DEF.

This damn thing is $3.66/gallon to go 24 miles.
15.25¢ per mile....

The 6.2L is 12¢(19mpg combined) per mile WTH."