DEF Math

[BurbMan]

The owner's manual says my truck has a 5.5 gal DEF tank. I waited until I was down to 1/4 on the gauge, just above the red zone, and added a 2.5 gal box of Blue DEF from Advance Auto. Now the gauge reads FULL to the top.

So the gauge must be set to give you a long warning zone to keep you out of limp mode. This is only my 2nd time adding DEF so just getting used to all of this.

Also interesting is that the DEF I got said "Blue DEF" but the Peak brand is gone, and so is the manufacture date. No date or code of any kind on the box or the container so no way to know how old it is. With tax it was $15 for 2.5 gals, so $6/gal. Probably last time I'm buying it at Advance.

[Lantley]

jaycocamprs wrote:

ktmrfs wrote:

two ways
1) my truck gives an initial warning at 30% which even worst case is at least 1,000 miles. Then it continues to count down and give warnings. If I'm dumb enough to ignore the gauge for 1,000 miles I get what I deserve.
2) DEF usage is about 1 gallon of DEF for 100 gallons of diesel. pretty easy to keep track of in my head.
3) If I'm traveling, before I leave I can have a pretty good idea based on last fill how many miles I can go before the 30% warning comes on. If I think I will be close, easy enough to put a 2.5gallon jug in the bed.

You need to keep that LML. #1 I've never seen a warning of more than 300 miles. And the mileage given isn't right, it's short 20-25%. And #2 the L5P sucks DEF. The one time I kept track of the fuel for a whole tank of DEF worked out to about 1 gal DEF to 45 gal diesel. That's twice the rate of the LML.

Exactly my L5P give some inaccurate warning mileage and threatens to go into limp mode! Good Grief! Sort of unbelievable that GM thought this was OK:h

[jaycocamprs]

ktmrfs wrote:

two ways
1) my truck gives an initial warning at 30% which even worst case is at least 1,000 miles. Then it continues to count down and give warnings. If I'm dumb enough to ignore the gauge for 1,000 miles I get what I deserve.
2) DEF usage is about 1 gallon of DEF for 100 gallons of diesel. pretty easy to keep track of in my head.
3) If I'm traveling, before I leave I can have a pretty good idea based on last fill how many miles I can go before the 30% warning comes on. If I think I will be close, easy enough to put a 2.5gallon jug in the bed.

You need to keep that LML. #1 I've never seen a warning of more than 300 miles. And the mileage given isn't right, it's short 20-25%. And #2 the L5P sucks DEF. The one time I kept track of the fuel for a whole tank of DEF worked out to about 1 gal DEF to 45 gal diesel. That's twice the rate of the LML.

[NJRVer]

I use Blue DEF from Walmart as a matter of convenience.
In the past month or so it seems like all of a sudden Home Depot and Lowes around me are on a massive Blue DEF push.

You used to see maybe 5 or 6 boxes in an out of the way location.
Now, pallets of the stuff right in your face as soon as you walk in the door in the contractor end of the stores. Prices are within cents of each other $12.25 - $12.50.

[tkcrawford]

Just for giggles, I just now looked up the price of Peak Blue DEF on the Canadian Wal-Mart (walmart.ca) page. You're not gonna believe this...

For one gallon of Peak Blue DEF at Wal-Mart the price is $78.97 with a shipping fee of $169.05. Now don't you all feel better?!

[Me_Again]

FishOnOne wrote:


The Ram def usage rate is not linear and will go down at a faster rate once the fluid gets down to a certain level. Not sure if Ford or GM does the same.

Usage is linear, however the gauge is not! Those are separate issues. Like Russ said, it is nice that RAM gave "us" a gauge. I like having it, as it makes it easy to know when to look for a WM and put in a box of Peak Blue DEF. All has been Peak Blue DEF except of the last one which for WM Supertech Jug, and I am going to run it lower before adding another box. All has been from WM except one in Wells, Nv from Love's.

[noteven]

Lantley wrote:

noteven wrote:
What we learned in the class 8 world is high EGT's (power demand) result in increased NOx emission which = increased DEF use. In a working class 8 truck that was around 1-2% DEF vs fuel.

If I owned a DEF using pickup I would measure in some DEF fills at the pumps vs fuel used and soon have a rate vs fuel use vs work we are doing today factor to know when to fill the DEF tank.
a shopping plaza or China parts store to buy DEF in a cardboard box down aisle 300.

In my case my DEF use is erratic because my truck is my daily driver. I'm not towing all the time.
Tying to calculate/predict my DEF use based on my driving habits is futile.
Just need a gauge!

Wanting a gauge for DEF is not unreasonable.

[rhagfo]

FishOnOne wrote:

rhagfo wrote:

Me Again wrote:

rhagfo wrote:

Cummins12V98 wrote:
15 RAM with gauge at 1/2 a 2.5 fits easily.

X2!

One has to use 1 to 1.5 gallons when the tank is full before the gauge even starts to move down. It is very slow at the top and more speedy on once the gauge starts moving.

While that may be true, at least Ram thought in give you a gauge. Ford and GM didn’t have them early on, and I am not sure if either has a gauge yet.

The 11-16 Super Duty's tells you "The exhaust system is OK", "under half full", and two different miles left warnings (don't remember the exact miles left messages). The '17-Up have a digital DEF gauge.

The Ram def usage rate is not linear and will go down at a faster rate once the fluid gets down to a certain level. Not sure if Ford or GM does the same.

I was a Ford man for about 45 years and most of my fuel gauges were not linear either. That and I could watch the file gauge needle move on our old 460 F250 ,twin 19 gallon tanks!

[FishOnOne]

Here's a video on DEF common problems. Crystallization and contamination being a couple of the big problems.

Link

[FishOnOne]

rhagfo wrote:

Me Again wrote:

rhagfo wrote:

Cummins12V98 wrote:
15 RAM with gauge at 1/2 a 2.5 fits easily.

X2!

One has to use 1 to 1.5 gallons when the tank is full before the gauge even starts to move down. It is very slow at the top and more speedy on once the gauge starts moving.

While that may be true, at least Ram thought in give you a gauge. Ford and GM didn’t have them early on, and I am not sure if either has a gauge yet.

The 11-16 Super Duty's tells you "The exhaust system is OK", "under half full", and two different miles left warnings (don't remember the exact miles left messages). The '17-Up have a digital DEF gauge.

The Ram def usage rate is not linear and will go down at a faster rate once the fluid gets down to a certain level. Not sure if Ford or GM does the same.

[rhagfo]

Me Again wrote:

rhagfo wrote:

Cummins12V98 wrote:
15 RAM with gauge at 1/2 a 2.5 fits easily.

X2!

One has to use 1 to 1.5 gallons when the tank is full before the gauge even starts to move down. It is very slow at the top and more speedy on once the gauge starts moving.

While that may be true, at least Ram thought in give you a gauge. Ford and GM didn’t have them early on, and I am not sure if either has a gauge yet.

[Me_Again]

rhagfo wrote:

Cummins12V98 wrote:
15 RAM with gauge at 1/2 a 2.5 fits easily.

X2!

One has to use 1 to 1.5 gallons when the tank is full before the gauge even starts to move down. It is very slow at the top and more speedy on once the gauge starts moving.

[Bionic_Man]

ShinerBock wrote:
Buy from the pump at truck stops. Not only is it fresh and stored in a cool place to last longer, but is also only costs about $2 per gallon.

My dealerships sells DEF. I can tell you that most of it sits out in a hot warehouse or in a hot semi-trailer for ages before being put out in the showroom which lowers the shelf life.

Between the cost savings, and being assured you have fresh, not expired DEF, I don't know why anyone would buy it in a box. Sure, it can be slightly inconvenient pulling up to the truck stop and running inside, but as sensitive as some report the fuel systems are it is worth the trouble.

Filled my Jeep up this week. It gets about 1500 miles/gallon of DEF, granted it is more DD, but is used to tow boats. That 8 gallon tank is nice. Not sure why the trucks don't use a bigger tank.

[FishOnOne]

Lantley wrote:

noteven wrote:
What we learned in the class 8 world is high EGT's (power demand) result in increased NOx emission which = increased DEF use. In a working class 8 truck that was around 1-2% DEF vs fuel.

If I owned a DEF using pickup I would measure in some DEF fills at the pumps vs fuel used and soon have a rate vs fuel use vs work we are doing today factor to know when to fill the DEF tank.
a shopping plaza or China parts store to buy DEF in a cardboard box down aisle 300.

In my case my DEF use is erratic because my truck is my daily driver. I'm not towing all the time.
Tying to calculate/predict my DEF use based on my driving habits is futile.
Just need a gauge!

I'm surprised you don't have some form of gauge. I use my truck as a daily driver and notice it uses less DEF during the cold months.

Bottom line after 8 years and 200k miles I never ran out and never had any DEF related issues using only Peak Blue DEF. I use a Ford brand DEF nozzles that prevents over fills that I clean and store it in the zip lock bag it came in. I typically add 2.5 gallons every ~6,000 miles

[Lantley]

noteven wrote:
What we learned in the class 8 world is high EGT's (power demand) result in increased NOx emission which = increased DEF use. In a working class 8 truck that was around 1-2% DEF vs fuel.

If I owned a DEF using pickup I would measure in some DEF fills at the pumps vs fuel used and soon have a rate vs fuel use vs work we are doing today factor to know when to fill the DEF tank.
a shopping plaza or China parts store to buy DEF in a cardboard box down aisle 300.

In my case my DEF use is erratic because my truck is my daily driver. I'm not towing all the time.
Tying to calculate/predict my DEF use based on my driving habits is futile.
Just need a gauge!