# 15 CTD DEF Usage



## IndyDiesel (May 24, 2015)

I had my DEF tank heater replaced under some special warranty at 44,500 miles maybe around Oct 2017, dealer topped off DEF when they performed replacement. Now I am at 58,500 and have driven 14,000 miles, my DEF % just hit 35% left, if I do a little math and ran to empty it would be 21,500 miles to a full tank of DEF. Obviously I won’t go that far but in theory could. I drive about 85% to 90% nighway miles. Just curious what others are getting in miles for DEF usage. I think they changed things for gen 2, it uses more as I understand it.


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## Rivergoer (Mar 30, 2017)

IndyDiesel said:


> I had my DEF tank heater replaced under some special warranty at 44,500 miles maybe around Oct 2017, dealer topped off DEF when they performed replacement. Now I am at 58,500 and have driven 14,000 miles, my DEF % just hit 35% left, if I do a little math and ran to empty it would be 21,500 miles to a full tank of DEF. Obviously I won’t go that far but in theory could. I drive about 85% to 90% nighway miles. Just curious what others are getting in miles for DEF usage. I think they changed things for gen 2, it uses more as I understand it.


Hey Indy, 

I never top off, just wait till 35% or so then pour in a full 2.5 gallon container from Walmart. For me it’s easier than pulling all my crap out of the trunk at a truck stop to use a DEF pump.

I went 8,000 miles on the 1st fill (2.5 gal). Since the last 2.5 gal fill I’ve gone 7,000 miles and DEF still reads “OK”. 

For reference my 2014 has 84,000 miles on the odometer. Cheers!


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## beaurrr (Aug 27, 2016)

Rivergoer said:


> Hey Indy,
> 
> I never top off, just wait till 35% or so then pour in a full 2.5 gallon container from Walmart. For me it’s easier than pulling all my crap out of the trunk at a truck stop to use a DEF pump.
> 
> ...


That sounds about right; 7 or 8,000 miles after dumping in 2.5 gallons when the indicator comes on at 35%. Now that I'm not driving much, I run it down to almost empty before I add 2.5 gallons.


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## LiveTrash (May 24, 2015)

From the rough estimates I did mine seems to get about 20,000 km per tank of DEF. Didn't do any proper math but from examining the odometer and comparing it to what I've been filling it up with, it seems to work out. I believe you're right about the Gen2, it uses more to probably meet higher emissions standards.

I'll personally let mine run for a little bit and typically allow it to give me a second warning after the first low DEF warning. I like to let it run through most of what's in the tank and then put in some fresh so it doesn't get stale (especially when it's constantly frozen throughout the winter time).


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## Tomko (Jun 1, 2013)

I’m about 15,000 miles per tank of DEF.


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## MP81 (Jul 20, 2015)

It looks like I average adding a 2.5 gallon jug between every 6,000 and 8,000 miles or so - really depends on how often my wife looks at the DEF screen, and then if she does, when (or more likely: if) that information is relayed to me.


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## mkohan (Dec 19, 2015)

Mine takes a little over 3 gallons every 10,000 mikes


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## Gator (Jul 14, 2013)

8000 miles I use a little under 2 gallons


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## sailurman (Sep 29, 2016)

That 35% indication is not accurate at all.


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## IndyDiesel (May 24, 2015)

I am over 15k miles now on a tank of def and percentages are 28% or so, I will let it go down a little more and add at a truck stop and will see how accurate it is on my car. Looks like highway miles we use less, city driving use more.


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## Rivergoer (Mar 30, 2017)

IndyDiesel said:


> I am over 15k miles now on a tank of def and percentages are 28% or so, I will let it go down a little more and add at a truck stop and will see how accurate it is on my car. Looks like highway miles we use less, city driving use more.


I know I go more miles between regens when those miles are all highway vs mixed city/highway. 

I’ve always wondered WHEN is DEF consumed...Full-time or only during Regen? I know diesel is injected post combustion to elevate EGTs over 1100F during Regen, is the diesel only burned during Regen or is DEF also used at that time?


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## MP81 (Jul 20, 2015)

DEF is used at all times - regen just temporarily increases particulate emissions (via increasing EGTs...via using more fuel) in order to clean out the DPF.


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## IndyDiesel (May 24, 2015)

If it’s used at all times on a gen 1 it’s a very small amount. If on highway you average 50 mph and it lasts 20000 miles that is 400 hours for about 5 gallons on DEF.


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## sailurman (Sep 29, 2016)

Good info. Thanks.


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## MP81 (Jul 20, 2015)

IndyDiesel said:


> If it’s used at all times on a gen 1 it’s a very small amount. If on highway you average 50 mph and it lasts 20000 miles that is 400 hours for about 5 gallons on DEF.


Yeah, it'll use less DEF where less NOx emissions are being produced, as it has less the SCR needs to convert.


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