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 > DEF when towing

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Toolguy5

Columbia Station, Ohio

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Posted: 03/05/22 10:17am Link  |  Quote  |  Print  |  Notify Moderator

What is your usage of DEF when towing. I have a 2020 GMC 3500 sierra 6.6 Duramax diesel.

I have 17000 miles on it now. Most of the miles are regular driving hardly use any DEF.
Had my truck serviced oil and filter change. Fuel filter changed as well as air filter changed. Dealer topped off with DEF. 3 days after service temperature got down around zero with a brisk wind. Received an message bad DEF 100 miles to slow down. Message disappeared on way to dealer when the truck warmed up. Dealer checked for codes and nothing. Next several weeks temperatures were in the teens. We left for Florida going through West Virginia and Virginia. Right before we got to Savannah received another message 1000 miles to reduced speed DEF. I had 2 1/2 gallons with me i filled it up. When we got to Florida I bought another 2 1/2 gallons and it took almost all of that. So I had just under 900 miles and that tank of DEF. On the way home I received the message again 998 miles i put 2 1/2 gallons in the gauge showed full. About 700 miles. Went another 375 miles and received message again 998 miles to slow down. Checked the gauge and still 3/4 full. I have an appointment for dealer to look at.

Towing a 14,000 lb fifth wheel speeds of 60 to 70 MPH.


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way2roll

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Posted: 03/05/22 11:58am Link  |  Quote  |  Print  |  Notify Moderator

I don't have the problem with the codes but I do use about 2x the def when towing. Makes sense, your engine is working harder.


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doughogue1

Flower Mound, Tx.

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Posted: 03/05/22 12:45pm Link  |  Quote  |  Print  |  Notify Moderator

I think the general rule is about 1% and that is about what I get while towing. 100 gal of diesel = 1 gal of def.

Toolguy5

Columbia Station, Ohio

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Posted: 03/05/22 04:25pm Link  |  Quote  |  Print  |  Notify Moderator

doughogue1 wrote:

I think the general rule is about 1% and that is about what I get while towing. 100 gal of diesel = 1 gal of def.


With what you are saying I was probably a little more the 1 gallon per 100 gallons

ktmrfs

Portland, Oregon

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Posted: 03/05/22 05:18pm Link  |  Quote  |  Print  |  Notify Moderator

doughogue1 wrote:

I think the general rule is about 1% and that is about what I get while towing. 100 gal of diesel = 1 gal of def.


yup DEF useage is basically determined by fuel useage. And the 1% number is a good "guestimate"

On my 2015 Denali over 60K miles average 1 gallon of DEF for 90 gallons of fuel.


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rhagfo

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Posted: 03/05/22 05:41pm Link  |  Quote  |  Print  |  Notify Moderator

I the last sentence you stated you have a gauge, just check it for level. The 1,000 miles to slow down just should not show up.
I would expect a 100 mile warning anything else is a bug.

Last thing DEF will freeze, so might be the reason for warnings, the heater may not have thawed it fast enough.


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Posted: 03/05/22 05:52pm Link  |  Quote  |  Print  |  Notify Moderator

I average 450 to 500 miles per gallon of DEF pulling 19.5K.
I've never gotten the 1000 mile warning, generally get the warning that I have 250 to 400 miles before DEF Empty.


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Thermoguy

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Posted: 03/05/22 06:10pm Link  |  Quote  |  Print  |  Notify Moderator

I fill my DEF tank before I take it in for an oil change every 5000 miles. Mostly towing and local driving. 2015 Chev 2500. I buy 2 of the 2.5Gal jugs but can not fit both of them in. I have only seen the low DEF waring once and purchased the truck new. Didn't stop or anything, just waited until I got home and filled as I had an oil change appt the next week.

Lantley

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Posted: 03/05/22 06:58pm Link  |  Quote  |  Print  |  Notify Moderator

Since GM decided I don't need a gauge I have no idea how much DEF I use.
I cannot trust the mileage warning simply because I'm not sure how it works, I assume its using total miles vs. towing miles.
When the mileage warning message comes on I make it a point to fill the DEF from a fuel pump not the leaky jugs.
DEF seams to work OK in terms of cleaning up the exhaust. But the implementation and logistics of the DEF system was poorly executed by GM.
No gauge, fill under the hood, exposed tank hanging down below running board, The entire system appears to be an after thought!


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rhagfo

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Posted: 03/05/22 08:42pm Link  |  Quote  |  Print  |  Notify Moderator

Just don’t understand not having a DEF gauge, on our Ram at 1/2 tank it will take a 2.5 gallon jug. Alwa wondering how much DEF I have left.

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