First time towing in the 3.0 Duramax - DEF usage?

redwngr · October 21, 2020

28 minutes ago, Carbon said:

I ended up using just over 3.5 gallons on my 1300ish mile trip towing. I added 2.5 when my display told me I had 300 miles remaining and it still showed 1/2 tank. when I got home i topped off with just over 1 gallon bringing the total to just over 3.5 gallons.

Was it topped off before the trip or just a gauge check or...?

What was the fuel usage/mileage for the trip?

DemonWorks · October 21, 2020

1 minute ago, redwngr said:

Was it topped off before the trip or just a gauge check or...?

What was the fuel usage/mileage for the trip?

topped off until it overflowed before I left and topped off the same when I returned.

mileage was roughly in the 17's after going to and from, was 17.8 one way and 16.x the other

redwngr · October 21, 2020

1300 miles / 17.5 miles per gallon = 74.3 gallons of fuel.

3.5 def/ 74 fuel x 100% = 4.7%, or 4.4 gallons def per 100 gallons fuel.

FWIW, that's about triple what my 6.6's seem to use.

(both on miles per def gallon and def/fuel ration basis)

Edited October 21, 2020 by redwngr

DemonWorks · October 26, 2020

Part 1 of 2, I didn't realize how much time the footage took up. Some hill climb videos didn't make it, unfortunately. My trip back (part two) had some good hill videos as well as my def usage. Stay tuned for that.

Desmo · October 28, 2020

I just did a round trip from Salt Lake City to San Diego, towing a 7x16 cargo trailer. My MPG ranged from 9-12 when towing at 75MPH and I got around 15 when towing at 55-60MPH. I did not calculate DEF usage, but it was horrible. I assumed that if I topped off before the trip that I would make it back, but not even close. When I got to SD the warnings started to appear, so I added 2.5 gallons of DEF, the gauge then read full. On the way back, more steep uphill climbs, I was not taking it easy, I wanted to really test the LM2, by Mesquite NV more warnings and the gauge showed one red bar. Assuming that the tank was empty I purchased two 2.5 gal. jugs at Walmart and after about 3 gallons in the tank overflowed. Arriving back home the gauge was down a only a few bars (1/2 to 3/4 tank), but after taking it out of tow mode and putting a few miles on it the warnings came back. I added my remaining DEF from the overflow situation and still had to run errands all day before the thing realized there was enough DEF or the estimated miles to empty DEF was back to normal.

My take-away, the "calculated" gauge and warnings based on estimated miles of DEF are a joke. The consumption seems reasonable but whats the point of a 5+ gallon DEF tank that you only get to put 3 gallons into before the truck turns itself into a paperweight... Seems like a flaw or bad programming or bad design from GM, hopefully they realize this and a recall on the tank/sensor or a software update is coming. Next long towing trip, I'm packing a couple jugs of BlueDEF. and I'll keep my speed closer to 70MPH and keep my foot out of it on the hills.

Overall, wow, the power of this 3L DMAX (backed by the 10L80) is impressive, no drama towing, just set the cruise and watch for the other dummies on the road.

Edited October 28, 2020 by Desmo

DemonWorks · October 28, 2020

32 minutes ago, Desmo said:

I just did a round trip from Salt Lake City to San Diego, towing a 7x16 cargo trailer. My MPG ranged from 9-12 when towing at 75MPH and I got around 15 when towing at 55-60MPH. I did not calculate DEF usage, but it was horrible. I assumed that if I topped off before the trip that I would make it back, but not even close. When I got to SD the warnings started to appear, so I added 2.5 gallons of DEF, the gauge then read full. On the way back, more steep uphill climbs, I was not taking it easy, I wanted to really test the LM2, by Mesquite NV more warnings and the gauge showed one red bar. Assuming that the tank was empty I purchased two 2.5 gal. jugs at Walmart and after about 3 gallons in the tank overflowed. Arriving back home the gauge was down a only a few bars (1/2 to 3/4 tank), but after taking it out of tow mode and putting a few miles on it the warnings came back. I added my remaining DEF from the overflow situation and still had to run errands all day before the thing realized there was enough DEF or the estimated miles to empty DEF was back to normal.

My take-away, the "calculated" gauge and warnings based on estimated miles of DEF are a joke. The consumption seems reasonable but whats the point of a 5+ gallon DEF tank that you only get to put 3 gallons into before the truck turns itself into a paperweight... Seems like a flaw or bad programming or bad design from GM, hopefully they realize this and a recall on the tank/sensor or a software update is coming. Next long towing trip, I'm packing a couple jugs of BlueDEF. and I'll keep my speed closer to 70MPH and keep my foot out of it on the hills.

Overall, wow, the power of this 3L DMAX (backed by the 10L80) is impressive, no drama towing, just set the cruise and watch for the other dummies on the road.

Looks like I had good wind resistance vs you towing a wall?

That's crazy on the usage of DEF for yours, I may be towing an enclosed trailer in december and will be able to compare once again.

Here's the video of my return trip:

Desmo · October 28, 2020

11 minutes ago, Carbon said:

Looks like I had good wind resistance vs you towing a wall?

That's crazy on the usage of DEF for yours, I may be towing an enclosed trailer in december and will be able to compare once again.

Yeah, cargo trailers are like parachutes. Good luck on your trip, I bet as long as you're not in a hurry and just take it easy the DEF usage will be manageable. Pack extra DEF, it can't hurt.

On 10/21/2020 at 10:02 AM, redwngr said:

1300 miles / 17.5 miles per gallon = 74.3 gallons of fuel.

3.5 def/ 74 fuel x 100% = 4.7%, or 4.4 gallons def per 100 gallons fuel.

FWIW, that's about triple what my 6.6's seem to use.

(both on miles per def gallon and def/fuel ration basis)

This concerns me, does more DEF injection mean less emissions or did someone at GM do the math wrong? If I got triple the DEF range when I was towing, I'd be very happy.

But so many factors to consider, fuel, load, engine management... Maybe towing the same thing, the load on the 6.6 would be less which makes the 3.0 a DEF guzzler.

akramer450 · August 20, 2021

I towed my 7x14 extra tall cargo trailer across canada. Truck used a fair bit of DEF going east with a tail wind in the prairies at 125km/h 75mph 20L/100km Northern Ontario was better as i was going slower. 110km/h or 65mph. 17.5L/100k

However, coming back west into the wind across the prairies. trying to do 125 as I wanted to get home. Fuel mileage got really bad. I had to slow down just to make it to the next major city to fill up. 23L/100km Def usage was brutal. I used over 3 jugs for the 3600km trip back.

Now I also have a 3500 6.6Duramax that has pulled this trailer. It does trips to the USA alot, it averages the same fuel mileage roughly 17.5 to 20L/100km. But uses far less DEF. My thoughts are the exhaust system on the 6.6 is much larger and designed for towing. So it is probably better at handling the exhaust for the amount of fuel burned. The 3.0L dmax, while great at towing, i think it's main purpose is commuting. If you're towing, bring lots of DEF.

Rvfool · September 11, 2021

I eat DEF when I tow my 7200 lb Travel trailer. Add 2.5 galleons in Flagstaff AZ and showed 70% full on idash. Soot load 8%. Drove to Las Vegas NV (about 240 Miles), going 65 mph on cruise control. Got of Vegas and said I had only 247 mile left message. Still showed 53% def on Idash and dash bar display. I have this condition before. It would get to 150 miles left then 10 miles later say limiting speed to 65 mph in 100 miles. Once it even said I was out of def. the gage system is total unreliable on the 3.0 l. You need to carry DEF with you when you tow as the 3.0 is a DEF Hog when you Tow. What is funny you can see you soot load being reduce while towing but not around town when not towing. Around town it increases until you get to 100% then it going into active regen. Never see regen active with towing but acts like it is in regen.