3.0 Duramax AT4 - Great so far

MPX1 · May 22, 2021

Since most forum posts consist of folks' negative experiences with anything and everything, I figured I'd post about my positive experience with the 3.0 Duramax up to this point. Granted, I haven't had it long. I've put about 1000 miles on it - most of that has been city driving. Lots of short trips, idling, etc. A few highway drives here and there.

I've had zero issues with the truck or the engine up to this point. It seems like a lot of the posts here show issues with the Duramax within the first 1000 miles or so (throwing codes, trips to the dealer for xyz, on and on). It drives incredibly well and has even seemed to smooth out and drive better past the early break-in period.

For prospective buyers of the 3.0 - this likely won't go over well with the traditional diesel guys, but don't listen to them. Old-school (and even some "newer" school) diesel rules don't really apply to this engine. If you look at the design, it was built with the daily driver in mind. Being that the exhaust system has always been an issue for diesel trucks built over the last decade or more, it seems that GM went out of their way to make that mostly a non-issue on this truck.

The engine is small, so it doesn't take long to get up to temp. Combining the DPF and the SCR into one unit and placing it next to the engine makes it far more efficient and exposes it to more heat more often. In my first thousand miles, I've only noticed one regen (I'm not using a OBD to track...I don't care to get that granular). It's likely had more than one, but I've only "noticed" one. AND...it occurred over multiple short trips around town. It completed on its own with no issues. There was a day where I had to bounce around town and do a bunch of ******, and over the course of a couple hours and probably 6-7 destinations with tons of stop and go, the regen ran through the cycle and completed on its own. No problem.

I'm sure plenty of diesel guys will show up here and tell me how wrong I am and how I'm asking for issues, but keep in mind - GM is putting this engine in a bunch of family cars and heavily incentivizing people to move in that direction (no-cost upgrade on the Escalade, $995 on most other vehicles). Being that this is one of the few diesel engines in America that wasn't sourced from a European manufacturer and repurposed for the US (clean sheet design, etc), it seems like GM really put a ton of effort into figuring out the exhaust system issues. Being that warranty repairs cost the manufacturer money, it doesn't make a ton of sense that they'd put these in cars that would idle a ton and be subjected to stop-and-go traffic if it were going to cause a boatload of issues. People freaked out back in the day when gas engines were forced to use catalytic converters and such. Eventually, manufacturers figured it out and now they're a non-issue. I feel like this engine has been a big step in that direction for diesel.

I may eat crow and come back here cursing myself for purchasing the diesel down the road, but so far it's been great and I couldn't be happier with this truck. It's an absolute joy to drive on a daily basis.

I'll keep this thread updated as my ownership progresses.

jbjlock26 · May 28, 2021

I have less than 700 miles on mine. Very pleased with performance and full economy. What coolant temp are you seeing in normal highway driving. I notice the gauge is 210 straight up and I'm seeing just slightly above that.

Grover67 · May 29, 2021

Your engine temp is normal jbjlock26. If you haven't read up on the 3.0l on how it operates might check it out

-grover67

MPX1 · June 14, 2021

On 5/28/2021 at 6:14 PM, jbjlock26 said:

What coolant temp are you seeing in normal highway driving. I notice the gauge is 210 straight up and I'm seeing just slightly above that.

Late reply here, but yeah same - 210. Kind of floats around that. I've noticed during regens that it'll kick a notch higher here and there and then settle back down to 210 when it's done.

This thing is going on some long road trips in the next few months so I'll have a lot of mileage to report. Still great though at 1700 miles. No issues.

swervin36 · June 15, 2021

I bought mine last May, it now has 16500 on it with no issues. I have to agree with MPX1. 1/2 Ton trucks are daily drivers and grocery getters. Time will tell but I love this truck.

z28tranz · June 15, 2021

I purchased a 21 AT4 with the 3.0 Duramax and I can't wait for it to come in. I drive 68 miles round trip 4 days a week so it will be nice to not have to drive my gas guzzling Tahoe.

Hamidar05 · June 16, 2021

9 hours ago, z28tranz said:

I purchased a 21 AT4 with the 3.0 Duramax and I can't wait for it to come in. I drive 68 miles round trip 4 days a week so it will be nice to not have to drive my gas guzzling Tahoe.

I bought a Tacoma for good mileage and get 21 MPG combined, but looking forward to my LTZ 3.0l and even better mileage in a bigger truck!

z28tranz · June 16, 2021

6 hours ago, Hamidar05 said:

I bought a Tacoma for good mileage and get 21 MPG combined, but looking forward to my LTZ 3.0l and even better mileage in a bigger truck!

I traded my 20 TRD Offroad 4x4 Tacoma for the AT4. The Taco was a great truck but it was just a little too small and for being a V6 it got crap gas mileage, I might as well of had a V8.

MNJoel · June 16, 2021

I''ve got 4,100 on my baby diesel and just did a 2k mile trip in it. I averaged 23.5 mpg with all 75-85 mph highway speeds. Pretty damn good for the little diesel. Way better than my 5.0 F150 that would average 14-15.

MPX1 · July 18, 2021

Wanted to update - 3700 miles after a 1200-ish mile road trip last week.

I know I'm still very early in the ownership period for this truck, but if I wasn't 100% sold on the 3.0 Duramax before my long trip, I am now. I honestly can't say enough positive things about this powertrain, not to mention the AT4 itself.

Truck was loaded up with my wife and daughter and the dog and a bed full of luggage and gear. On the way out to the Carolinas via I-40, I hand-calculated 27 mpg. I usually try to keep between 70-80 on the highway.

My best 50 mile run was 38 mpg, with the worst being about 22 and that was during a stint of driving...uh...fast. Haha.

Zero issues, diesel is an absolute beast. TONS of passing ability on the highway which surprised me. It won't put you in the back of the seat like maybe the 6.2 would, but it's more than enough. They really found a way to make this engine sing at all speeds.

Extremely comfortable, and the camera system was clutch in the mountains. Getting into and out of tight spaces where a wrong move could send a corner of the vehicle over a ledge was made stupid easy with the cameras. Love this truck.

MPX1 · August 27, 2021

Alright so my "great so far" ended today.

4700 miles and had a no-start crank this morning during a remote start. I posted the details on the main thread on this forum where people seem to be keeping an eye on this issue.

I jumped in the truck immediately and saw a message on the DIC that said something to the effect of "service steering column." I only saw it for a split second before it disappeared so that definitely isn't exactly what it said, but that's the best I can recall. It started immediately afterward and has started fine the rest of the day. Add my truck to the list of trucks with this issue apparently....

2021DENALI1500 · September 7, 2021

On 8/26/2021 at 9:17 PM, MPX1 said:

Alright so my "great so far" ended today.

4700 miles and had a no-start crank this morning during a remote start. I posted the details on the main thread on this forum where people seem to be keeping an eye on this issue.

I jumped in the truck immediately and saw a message on the DIC that said something to the effect of "service steering column." I only saw it for a split second before it disappeared so that definitely isn't exactly what it said, but that's the best I can recall. It started immediately afterward and has started fine the rest of the day. Add my truck to the list of trucks with this issue apparently....

My truck just did this while I was on a trip to SC. Since then I’ve returned home and it hasn’t done it again. My baby duramax currently sits at 3k miles… not too worried about it TBH. If the problem persists a trip to the dealer will ensue.

8x180 · September 12, 2021

bla bla bla

Edited September 13, 2021 by 8x180

Sqrls · September 13, 2021

As far as weird intermittent issues, I’ve noticed if we have strong windy storms overnight, the next day I may have a random reboot of the software or random electrical glitches that clear up. I’m guessing at an angle water can get into some electronics, but I’ve never had it after washing it or normal rain.
With the temperature gauge, it seems like it will overheat a touch to help the oil or engine heat evenly. It’s not a true overheat because anytime I get annoyed with it, if I hit the gas the temp gauges literally plummets back to normal. If it was actually not keeping up with cooling, the opposite should happen so it’s not something to worry about and that’s a good way to get myself not to worry about it lol.

Towards max load with a trailer on 90 degree or warmer days if I’m spiritedly accelerating through traffic, I do notice the gauge slightly on the high side of the the middle notch, and responsiveness of the engine seems throttled back compared to the start of the trip with the same load.