2018 FreightLiner DEF Consumption Specifications

[turbopilot]

I have been operating diesel truck powered RV's since before the big 2010 EPA crackdown on PM and NOx emissions. My first truck just had a DPF in the exhaust system using extensive EGR to control NOx. EGR was a problem since it lowered fuel economy and increased particulate loading.

In 2012 I took delivery of one of the first diesel engines using SCR by adding DEF to the exhaust after treatment to further drive down the NOx to conform with increasingly stringent EPA regulations. The first SCR/DEF after treatment systems used very little DEF, typically 1 to 2 % of fuel flow. While still relying on EGR to drive down NOx.

The latest series of Diesel engines from Cummins now us SCR as the primary component to lower NOx but the key is they need to use a lot of DEF as they pull back on EGR to do the job. Using more SCR/DEF and less EGR increases fuel economy and decreases PM generation so there are some good economic trade offs.

This brings us to 2018. Folks buying 2018 DP will notice that the DEF tank capacity has significantly increased over the last few years. My last 6.7 liter Ford diesel had a 6 gallon tank that seem to last for ever, while my New Aire has a 17 gallon tank that drains quickly.

If you do searches on line of expected DEF consumption most sources point to performance in SCR equipped diesel built before 2013. These engines would nominally consume DEF in gallons equal to 2% of fuel consumption.

But for 2018 the DEF consumption numbers have significantly changed. Since getting delivery of my NA I have consistently logged DEF consumption. In my NA I am seeing DEF usage equal to around 5% of fuel usage. This is way out of line with my expectation. I have now talked to both FreightLiner and Cummins about my coaches excessive use of DEF. Cummins sent me documentation showing that my engine is specified to use between 3 and 5 percent of fuel flows in DEF. So neither company will even troubleshoot my engine for excessive DEF use. It is considered normal.

Some of you have suggested that you are seeing lower DEF usage in post 2013 FreightLiner models which is great, but for the rest it appears up to 5% DEF usage is the new normal. Apparently throwing much more DEF at the exhaust was the only to comply with new EPA standards.

[Stuart W]

17 gallons of DEF on a New Aire seemed high, just looked and its 10 gallons, not sure if this effects your calculation. My DS has a 15 gallon DEF tank and I used 4 gallons for 105 gallons of fuel, 4%

[Carefree]

On our 2016 DSDP it seems that I'm constantly adding DEF. Your calculations seem spot on. I remember laughing at the Freightliner Camp when Mike said I should be able to drive the coach across the country and back with one tank of DEF - not gonna happen. Just as I'll never see 8 mpg diesel consumption (another one of his statements).

[Stuart W]

By the way, I purchased 2.5 gallon containers of DEF @ Walmart for $7.98 each, wasn’t to bad, convenient with a nice poor spout.

[turbopilot]

Originally Posted by Stuart W

17 gallons of DEF on a New Aire seemed high, just looked and its 10 gallons, not sure if this effects your calculation. My DS has a 15 gallon DEF tank and I used 4 gallons for 105 gallons of fuel, 4%

Newmar information is wrong for the New Aire. FreightLiner site states 15 gallons for the DEF tank. I measured the physical volume of my tank and I came up with 17 gallons short of air space above the filler. In any event it has at least 15 gallons useable.

All the DEF related documentation I can find on the Cummins/FreightLiner web sites uses consumption data for pre 2014 engines.

[Stuart W]

That’s good as ratio of on board fuel to DEF. I hold twice the fuel with the same size DEF tank...makes me think FL anticipated high usage on your engine design

[turbopilot]

Originally Posted by Stuart W

That’s good as ratio of on board fuel to DEF. I hold twice the fuel with the same size DEF tank...makes me think FL anticipated high usage on your engine design

About 2,200 miles of DEF range in my NA. Neat thing about NA is that it is relatively easy to use auto diesel pumps but with limited DEF range I am forced into truck lanes to get to the DEF pumps.

The other issue not talked about much is the need to keep the DEF tanks full to avoid problems. Running these DEF tanks low can foul the measurement systems with DEF crystals. There is a Cummins service letter on this issue. Most crystals will come into solution in time when the are back under the fluid level but it may take a while, at the same time throwing MIL lights for low DEF.

[Stuart W]

@ 375 gallons of fuel @4% DEF usage = 15 gallons of DEF
375 gallons of fuel X 6.5 MPG = 2437 miles driven I understand that without over filling the DEF tank this would not be ok to go this low on DEF

[turbopilot]

Originally Posted by Stuart W

@ 375 gallons of fuel @4% DEF usage = 15 gallons of DEF
375 gallons of fuel X 6.5 MPG = 2437 miles driven I understand that without over filling the DEF tank this would not be ok to go this low on DEF

My goal based on previous experience with DEF level measurement systems is to keep the bottom half of the DEF measurement sensors under the DEF fluid level. For my NA this gives me a nominal DEF range of around 1,000 miles.

[Dutch Star Don]

"turbopilot".....there can be many reasons for excessive DEF usage, including your driving habits. You don't say what mpg you're getting, but my guess would be that small engine is working hard to push that heavy coach. Your math says you're within limits of DEF usage. Break in time may also be a factor.

I track everything on my coach, with the exception of DEF usage. It just isn't an issue or something I feel that needs to be tracked, especially that it's almost impossible to keep track of how much you use, unless you fill up at a pump. Out west, DEF pumps are few and far between. When my tank gets to about half, I pick up two containers at Walmart and refill. This has worked well for 4 years and a coast to coast trip.

Just enjoy the coach and don't worry if it's using 2%, 3% or 4%. It doesn't really matter in the big scheme of things.

[turbopilot]

Originally Posted by Dutch Star Don

"turbopilot".....there can be many reasons for excessive DEF usage, including your driving habits. You don't say what mpg you're getting, but my guess would be that small engine is working hard to push that heavy coach. Your math says you're within limits of DEF usage. Break in time may also be a factor.

I track everything on my coach, with the exception of DEF usage. It just isn't an issue or something I feel that needs to be tracked, especially that it's almost impossible to keep track of how much you use, unless you fill up at a pump. Out west, DEF pumps are few and far between. When my tank gets to about half, I pick up two containers at Walmart and refill. This has worked well for 4 years and a coast to coast trip.

Just enjoy the coach and don't worry if it's using 2%, 3% or 4%. It doesn't really matter in the big scheme of things.

Don, your post is not helpful and full of inaccuracies. There are plenty of DEF pumps out West. I know because I have been visiting them frequently with my new coach. Miles per gallon is totally irrelevant when it comes to DEF usage. DEF usage is calibrated to the amount of fuel burned. The after treatment equipment has no idea how efficiently the truck does that job moving down the road.

I have been operating large truck diesel engines since the beginning of EPA mandated after treatment began (five including my new FreightLiner). Until now none of those engines ever used more than 2% of fuel flow in DEF. My new FreightLiner engine is now using 5% of fuel flow in DEF. Cummins documentation states it should use no more than 2% (which I now know is outdated).

Cummins has now confirmed to me in writing the DEF usage up to 5% of fuel flow is now "normal" in order to comply with recent EPA changes to the permissible level in NOx emissions.

So with all due respect you don't need to tell me what not to worry about. I have a new machine and I am trying to determine if it is operating normally. I would guess other owners of 2018 FreightLiners would be interested as well.

[NealC]

turbo you’re out of line. He was not being condescending. He was just encouraging you to enjoy your NA and back off the microscope. But we all know you enjoy the dissection of your coach more than camping. To each their own.

Back to DEF. While I don’t have stats my consumption is very low. ISL9 400hp. I don’t even carry DEF anymore. Nor do I worry about it getting low. About when it’s half way I’ll find a pilot/flying J and fill up. Even when you run out of DEF you can drive 1000mi and find def. Turn the engine off and you’re done.

Happy camping or whatever your joy.

[turbopilot]

Originally Posted by NealC

turbo you’re out of line. He was not being condescending. He was just encouraging you to enjoy your NA and back off the microscope. But we all know you enjoy the dissection of your coach more than camping. To each their own.

I see it differently. Look up the definition of condescending.

For others interested in the facts about this issue technology and regulations have been changing constantly since EPA cracked down on NOx emissions starting in 2007.

Initially most engine makers relied on EGR to knock down NOx. That came with a big penalty in efficiency and particulate production leading to EGR maintenance issues and DPF issues. As the regulations tightened more in 2013 some engine makers began to back off aggressive EGR in favor of throwing more DEF at the problem. More DEF helped with better fuel economy, EGR issues and DPF issues. Some think that trade off was worth it when you considered the full cost (ie fuel, DEF and maintenance).

In recent years the VW diesel disaster has made the engine manufacturers more concerned with meeting emissions goals across the fleet, so I am guessing (my guess, no data) that they have been turning up the DEF spigot a little more "just in case".

Whatever the reasons, it is clear those with 2018 engines will likely be getting more experience using the DEF pumps.

[Newaire1]

Hey Turbopilot

You are 100% correct. I just googled the issue and read plenty about others seeing new engines burning way more DEF. So that is a big change being kept quite. All my previous engines went forever on a tank of Def. My Sprinter Chassis Motorhome would go 5000 miles. My GMC pickup could go 8000 miles. A 25 gallon tank should have been used at the very least on the New Aire.
The EPA is now being run with less radical leadership. Today they announced rolling back the 50 MPG mandate for cars that would have taken effect in a few short years. So maybe common sense regulations may come in to play and allow reflashing these engine computers to a reasonable emission level or not.
Looks to be lazy engineering. Fixing one issue with no regard to the effect of the change downstream. Cranking DEF use up 250% and not addressing tank size?
It’s like having a 7 gal tank At the old use rate! Oops, somebody wasn’t thinking.