Hitting the def a little hard

[Makensmoke]

I am going through 1 gallon of def per tank of fuel.

Any common reasons why?

#heavydrinker

 

[Ltngdrvr]

You think ONE GALLON OF DEF per tank of fuel is a lot???

DEF usage follows fuel usage, lower fuel economy means higher DEF usage.

But, one gallon per tank of fuel ain't much.

 

[kthaxton]

Non towing use.....one gallon per tank is a lot.....however I do not have any suggestions as to what is going on.

 

[AH64ID]

I am going through 1 gallon of def per tank of fuel.

Any common reasons why?

#heavydrinker

That doesn't sound too far out of range, depending on what kind of fuel economy you're getting.

How do you know it's 1 gallon? Filling at the pump or with a box?

2-3% is what is advertised for the rate of DEF to fuel. 3% of 30 gallons is .9 gallons.

My 18 seems to burn a little less than advertised at an average of 1.64%. Mixed lifetime DEF MPG 872, Diesel MPG 12.9.

 

[bcbender]

Mine has been right at about 500mpg for the first 5000 miles, I have mixed towing with lifetime average of 13.3mpg. So that's about 37:1 and I have a 32g tank... so yep.. 1 gal / tank.

 

[Makensmoke]

I am glad I asked before taking it in! I am around 11-12 mpg average as most of the time I am pulling a trailer. I have blotches of def on the front of my trailer and I was following my wife recently driving the truck and noticed quite a bit of clear liquid running out the pipe. I also have noticeable white inside my tailpipe and I hear the clicking noise I am told is the def pump clicking very fast quite often.

All seems excessive but if it is normal I’m good with putting in a box every 2.5 tanks of fuel.

 

[AH64ID]

Leaking DEF is NOT normal, something is certainly wrong.

 

[Ltngdrvr]

I am glad I asked before taking it in! I am around 11-12 mpg average as most of the time I am pulling a trailer. I have blotches of def on the front of my trailer and I was following my wife recently driving the truck and noticed quite a bit of clear liquid running out the pipe. I also have noticeable white inside my tailpipe and I hear the clicking noise I am told is the def pump clicking very fast quite often.

All seems excessive but if it is normal I’m good with putting in a box every 2.5 tanks of fuel.

No, you have an issue. Tailpipe should not be coated in dry DEF, and none should be blowing out of the pipe.
Sounds like you have a pump or injector sticking issue, it should be turning on the check engine light and posting a code.
Now, had you stated these conditions in your original post, we could have saved some time.

 

[JR]

Are you sure the stuff coming out the pipe wasn't condensate?

What are you seeing on your trailer? Pics?

I would certainly think if DEF was running out the tail pipe you would have tripped a CEL long ago. These trucks don't have much leeway when it comes to monitored parameters like this.

 

[Makensmoke]

Are you sure the stuff coming out the pipe wasn't condensate?

What are you seeing on your trailer? Pics?

I would certainly think if DEF was running out the tail pipe you would have tripped a CEL long ago. These trucks don't have much leeway when it comes to monitored parameters like this.

It sure could be condensate, it’s still chilly up here. The def on my trailer and bed cover could have found it’s way up from a drip hanging underneath after spilling from a truck stop fill station I suppose. It does not do it regularly, but it was the same spider web crusty residue consistent with dried, spilled def.

I have no CEL and it sounds like my mpg is typical.

 

[Makensmoke]

No, you have an issue. Tailpipe should not be coated in dry DEF, and none should be blowing out of the pipe.
Sounds like you have a pump or injector sticking issue, it should be turning on the check engine light and posting a code.
Now, had you stated these conditions in your original post, we could have saved some time.

No worries sir, I am in no hurry. Life is good.

 

[bcbender]

I would suspect condensate, not sure where DEF would actually come from in that volume that far back. My pipe looks similar to yours with the "condensate river" and I only have 5000 miles on it.

 

[brucejohnson]

Here are some excerpts from a very informative article with regard to DEF:

STEP 1: DEF Becomes Ammonia and Isocyanic Acid: (NH2)2CO → NH3 + HNCO

STEP 2: The Isocyanic Acid chemically breaks down with water into Carbon Dioxide and Ammonia:
HNCO +  H2O → CO2 + NH3 overall which is this: (NH2)2CO + H2O → 2NH3 + CO2

STEP 3: At this point during the chemical reaction Ammonia will, in the presence of oxygen and a catalyst, will reduce nitrogen oxides:
2NO + 2NH3 + ½O2 -> 2N2 + 3H2O and 3NO2 + 4NH3 -> 7/2N2 + 6H2O

STEP 4: The overall reduction of NOx by urea is:
2(NH2)2CO + 4NO + O2 → 4N2 + 4H2O + 2CO2 and 2(NH2) 2CO + 3NO2 -> 7/2N2 + 4H2O + 2CO2
​

Or, in more simple terms:

The vast majority of these systems use diesel exhaust fluid (mixture of urea and deionized water) sprayed into the exhaust system to break down the generated NOx into harmless nitrogen and water molecules.
​

Chances are all is well and good.

​

 

[p-Bar]

I'm using about a gallon per 1k mi.

 

[brucejohnson]

I'm using about a gallon per 1k mi.

Same here with the pavement princess at just over 4,100 miles. No heavy towing...yet.

 

[bcbender]

Does DEF usage differ between the STD eng / 68RFE and the HO eng / AS69RC?.... Mine has been pretty steady but I do about 50% towing

 

[Jim W]

This is from the Cummins filtration page on DEF.
They have provide this claim, that for every 50 gallons of diesel fuel used you should use about 1 gallon of DEF or about 2% of fuel usage. I can't say one way or the other since I do not use DEF. But this seems about right with my youngers son 2013.5 truck when he was using DEF in it.

Here is the link to the Cummins Filtration pages.
MB10033.pdf (cumminsfiltration.com)
On the sixth page they explain usage numbers on medium duty and heavy duty trucks.

 

[bcbender]

They have provide this claim, that for every 50 gallons of diesel fuel used you should use about 1 gallon of DEF or about 2% of fuel usage.

Sounds about right... some will be above, some below based on usage, speed, load, etc...

 

[AH64ID]

Does DEF usage differ between the STD eng / 68RFE and the HO eng / AS69RC?.... Mine has been pretty steady but I do about 50% towing

It will differ based on variances in tuning, power, and the 19+ compression ratio differences.

As power increases EGR use decreases, so DEF consumption goes up. That’s why I go from ~1000mpg DEF empty to ~500mpg DEF towing.

 

[JR]

A friend of mine owned a 15 prior to his 20. He is pretty meticulous with his logs and says the 20 drinks alot more fuel than the 15. Both SO trucks. I don't know exact numbers but he was quite surprised at the difference new truck to new truck.