3.0 Duramax - Regens, mileage, and the computer. Do I have a problem here?

redvettez06 · October 9, 2020

I just bought a dealer demo 3.0 Duramax and have put about 50 miles on it since I picked it up a couple of days ago (It is at about 1800 miles total now). This morning I noticed a slightly deeper rumble from the exhaust, and figured that a Regen was starting. I switched the display to fuel economy because I also have read that the regen process drops the gas mileage by a lot. It was reading on the gauge that the fuel economy was averaging 20 miles per gallon. I drove 30 miles on the highway to let the system do it's thing. The deep rumble went away at some point in the drive but the fuel economy on the computer never improved much more than a mpg or so. Am I missing something here or is the computer slow to respond in general or during a regen? The 2017 with the 6.2 engine that I had been driving had a computer that was very dynamic about adjusting the fuel economy report based on my driving. This thing seems like it hardly shifts at all and I am babying the hell out of it. Other that this little thing, I freaking love this truck and don't miss the 6.2L/8-speed combo at all.

newdude · October 9, 2020

Sounds normal to me. I'd keep driving it and get some more miles on it, seeing you've only driven it about 50.

Regens should occur once per tank of fuel, or approximately every 300-400 miles.

redvettez06 · October 9, 2020

Cool. yeah I tend to be paranoid about these things so I'm probably overreacting. Thanks for the insight.

redwngr · October 9, 2020

What trim level?

Different levels have different DIC, with different screens available.

Which fuel economy screen were/are you watching?

There is one fuel economy number with each of the trip meters -- they show the average since it was last reset -- many reset one of them each time they put in fuel. The more miles in the trip, the slower the average will change.

There is also a series of 'interval' graph displays that show intervals (like 25/50/400) - and have an instantaneous fuel economy number on them as well.

They will show the average for the most recent 25/50/400 mile interval.

The instantaneous number/bar graph will be the economy for the last few seconds.

The interval screens will show the average for the last xx miles, the instantaneous and the best xx miles. The 'best' number can be reset.

Duramax3oh · October 9, 2020

4 hours ago, redwngr said:

What trim level?

Different levels have different DIC, with different screens available.

Which fuel economy screen were/are you watching?

There is one fuel economy number with each of the trip meters -- they show the average since it was last reset -- many reset one of them each time they put in fuel. The more miles in the trip, the slower the average will change.

There is also a series of 'interval' graph displays that show intervals (like 25/50/400) - and have an instantaneous fuel economy number on them as well.

They will show the average for the most recent 25/50/400 mile interval.

The instantaneous number/bar graph will be the economy for the last few seconds.

The interval screens will show the average for the last xx miles, the instantaneous and the best xx miles. The 'best' number can be reset.

Excellent post I was going to say the exact same thing.

The "interval" graph would be the best to pay attention to for this matter to look at instantaneous and the 25 mile average. I reset Trip 1 each time I fill up the tank and I'm trying never to change Trip 2... I reset it as I drove off the lot so that I can easily see my lifetime miles and MPG. Next time you're able to spend half an hour or so playing around with this, find a good highway stretch that you can just set cruise control on 60 or 65 MPH and not have to change it due to traffic or turns. At that speed my 3.0L gets about 30 MPG if not a little more so you can do a comparison. If you're getting close to 20 MPG on that 25 mile trip setting then I'd start worrying more... unless it's extremely windy or you're driving uphill.

Lastly, keep in mind a dealer truck that's been test driven a lot will have a ton of engine hours of just sitting in park while people are looking at the features in the A/C and all. Not the best thing for the diesel engine so I say go spend some time doing highway driving and enjoy your new ride. It's a wonderful engine IMO. I'm like you though and really pay attention and worry about things. Don't worry but be aware and keep an eye on it. Good luck!

Ojustracing · October 15, 2020

On 10/9/2020 at 1:31 PM, newdude said:

Sounds normal to me. I'd keep driving it and get some more miles on it, seeing you've only driven it about 50.

Regens should occur once per tank of fuel, or approximately every 300-400 miles? try 180-300 not towing. More like 2 a tank minimum. My truck is getting 35+mpg tanks on average 3 regens a tank. Avg is 246 on mine. Even if I dont get lower mpg 28 tanks. still 2 regens a tank.

Every 300-400 miles between regens ? try 180-300 miles not towing. More like 2 a tank minimum. My truck is getting 35+mpg tanks on average 3 regens a tank. Avg is 246 on mine. Even if I do get lower mpg 28 tanks. still 2 regens a tank.

Edited October 15, 2020 by Ojustracing

Sqrls · October 15, 2020

3 hours ago, Ojustracing said:

Every 300-400 miles between regens ? try 180-300 miles not towing. More like 2 a tank minimum. My truck is getting 35+mpg tanks on average 3 regens a tank. Avg is 246 on mine. Even if I do get lower mpg 28 tanks. still 2 regens a tank.

My regen interval is nearly exactly like yours. I always have at least 1000lbs of weight in the truck so my mpg is a little lower, but that’s about right. With normal use, about 2 regens a tank. When towing, my mpg goes down obviously but still about 2 regens a tank (I do not tow long distance). The only time it really changes and it surprised me was on long highway trips, about 3 regens a tank.
I do have lots of city driving mixed in with my average use but I also don’t worry about mpg and don’t baby the throttle. Somehow, I’ve never had a tank average under 20mpg though compared to my 2018 5.3 getting 11-15mpg.

Ojustracing · October 15, 2020

3 hours ago, Sqrls said:

My regen interval is nearly exactly like yours. I always have at least 1000lbs of weight in the truck so my mpg is a little lower, but that’s about right. With normal use, about 2 regens a tank. When towing, my mpg goes down obviously but still about 2 regens a tank (I do not tow long distance). The only time it really changes and it surprised me was on long highway trips, about 3 regens a tank.
I do have lots of city driving mixed in with my average use but I also don’t worry about mpg and don’t baby the throttle. Somehow, I’ve never had a tank average under 20mpg though compared to my 2018 5.3 getting 11-15mpg.

Towing a 5k open car trailer netted 500 mile regen worst mpg was during this time calculated 20 mpg. just covered 4400 miles with a calculated mpg of 35.4 and 18 regens. But this is not highway driving 2 lane rural driving which the truck loves for high MPG

AlexB · October 17, 2020

I'm getting about 22-23mpg @75mph. How do you monitor when regen happens? I'm assuming it sounds different?

Ojustracing · October 18, 2020

16 hours ago, AlexB said:

I'm getting about 22-23mpg @75mph. How do you monitor when regen happens? I'm assuming it sounds different?

I use app on my phone and a wireless obd port adapter. Yes the exhaust will have a different tone and very easy to miss if you are the least bit distracted or have the radio on.

AlexB · October 18, 2020

I have the same app. Where is the regen option though? In the main list of things you can monitor?

Grover67 · October 19, 2020

19 hours ago, Ojustracing said:

I use app on my phone and a wireless obd port adapter. Yes the exhaust will have a different tone and very easy to miss if you are the least bit distracted or have the radio on.

Where can you pick the adapter up from?

-Grover67

AlexB · October 19, 2020

Grover: I have a cheapo one off of Amazon. Bluetooth version

yousaveone · October 21, 2020

Just drive it but remember diesels want to get warmed up and drive. They aren't great for short trips. Disable your start-stop.

3.0L_Johnny · December 11, 2022

On 10/9/2020 at 11:04 AM, redvettez06 said:

I just bought a dealer demo 3.0 Duramax and have put about 50 miles on it since I picked it up a couple of days ago (It is at about 1800 miles total now). This morning I noticed a slightly deeper rumble from the exhaust, and figured that a Regen was starting. I switched the display to fuel economy because I also have read that the regen process drops the gas mileage by a lot. It was reading on the gauge that the fuel economy was averaging 20 miles per gallon. I drove 30 miles on the highway to let the system do it's thing. The deep rumble went away at some point in the drive but the fuel economy on the computer never improved much more than a mpg or so. Am I missing something here or is the computer slow to respond in general or during a regen? The 2017 with the 6.2 engine that I had been driving had a computer that was very dynamic about adjusting the fuel economy report based on my driving. This thing seems like it hardly shifts at all and I am babying the hell out of it. Other that this little thing, I freaking love this truck and don't miss the 6.2L/8-speed combo at all.

They regenerate way too often for my liking, which makes it sound like a coffee can full of marbles and kills the gas mileage. It's the one poison pill about this engine. It'd be incredible to see what it could do deleted, but I'm not touching any of that until the powertrain warranty expires.