GMC AT4X - Diesel or Gas?

[nabatron]

The complicated emissions system is more likely to have issues IMHO. Doesn't mean it will happen, but higher chance of it.

The better MPG is nice on the diesel. When I originally got my 2020 AT4 3.0, diesel was actually a bit cheaper than gas at that time. So a win/win on diesel being cheaper (not by much, but a bit) and much better MPG (5 to 7 mpg better on mine over a gas truck). But the cheaper diesel didn't last long. At this point it is close to a wash on fuel cost diesel vs gas. Just shorter range on the 6.2 given they both have the measley 24 gallon tank.

As an example on lifetime MPG, my 2020 AT4 averaged 16.9 mpg on the lifetime trip meter. So far at almost 10K miles, my 6.2 AT4 is at 13.6 mpg. My MPG is lower because I pull a heavier, high wind resistance 16' enclosed job trailer (that is loaded to the gills inside) with a tall ladder rack on top with 6 larger extension ladders on it. Lots of wind resistance pulling that trailer on mountainous hwys here in MT. So my lifetime MPG is significantly lower because I pull my job trailer (along with a couple other trailers) as a contractor. On normal driving with no trailer, I get 15 to 16 on the 6.2. 20 to 22 is what I got on the 3.0 diesel. Similar sized tires/wheels with front level on both, so same situation with both trucks.

In my area of Canada the price of diesel is around 2 cents cheaper than gas but obviously depends on what gas station you go to. All prices are inconsistent in my area. Driving a hemi I know how terrible the gas mileage can be in a big V8 and I have the bigger gas tank as well. It’s funny in comparison the 6.2 even though it take premium and gets better has mileage then my hemi.

I already have wheels and tires from my ram that I will be switching over to the Sierra once I get it. Been reading up on tirile sizing and offset and seems like my mine should be able to fit with obviously trimming and a level.

 

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[nabatron]

I bought my 2022 at4 with the LM2 in September. I have about 8k miles on it. Awesome truck, great engine and trans combo. I had some minor emissions issue early on (loose claps, NoX sensor unseated). The dealer took care of the issues and got me a 3-year service plan for my troubles. I love this truck and engine. I recommend it for anyone who wants V8 power with better mpg. DEF usage will align with your MPG. I have 35’s on my truck, so my mpg averages 20 and I use a take of DEF every 4k miles.

That’s good to hear besides the minor emissions stuff. How’s the regen on the trucks? I’ll be doing mostly city and short trips to work. I know you have to do a long drive for the regen to burn off the soot.

 

[Teegunn]

In my area of Canada the price of diesel is around 2 cents cheaper than gas but obviously depends on what gas station you go to. All prices are inconsistent in my area. Driving a hemi I know how terrible the gas mileage can be in a big V8 and I have the bigger gas tank as well. It’s funny in comparison the 6.2 even though it take premium and gets better has mileage then my hemi.

I already have wheels and tires from my ram that I will be switching over to the Sierra once I get it. Been reading up on tirile sizing and offset and seems like my mine should be able to fit with obviously trimming and a level.

That's nice that diesel is cheaper than gas in your area.

I don't use premium, I have tried it a few times and noticed no difference in power or MPG, so the 30 to 50 cents extra a gallon doesn't seem worth it. Of course a big V8 is just not going to get good mileage, just how it is.

 

[nabatron]

That's nice that diesel is cheaper than gas in your area.

I don't use premium, I have tried it a few times and noticed no difference in power or MPG, so the 30 to 50 cents extra a gallon doesn't seem worth it. Of course a big V8 is just not going to get good mileage, just how it is.

So you are running 87? And don’t have any knock from the engine? I found it pretty surprising that GM says it recommends 93 on a naturally aspirated engine. I mean if it was boosted I could see using 91-93 but yeah doesn’t make sense with out a turbo or supercharger

 

[Teegunn]

So you are running 87? And don’t have any knock from the engine? I found it pretty surprising that GM says it recommends 93 on a naturally aspirated engine. I mean if it was boosted I could see using 91-93 but yeah doesn’t make sense with out a turbo or supercharger

Yes, 87, sometimes it is listed at 88 as some gas stations. But no knock, no issues. I remember a poster here that mentioned in a thread someone he knew well (may have been a family member) who works for GM, said that premium isn't needed in these 6.2's. I believe in that post, the person who works for GM said you might get 20 more horsepower from premium but otherwise no real benefit or risk using regular. Can't remember the thread the post was in however.

I think I put two tanks of premium in my 23 AT4X, and honestly didn't notice any difference. I did actually listened for knocks, etc, with premium vs regular, and never noticed any difference.

Most likely, long term, premium is better for the engine. I just can't bring myself to spend 10 bucks or so more a tank for premium. Maybe it will bite me in the arse down the line.... although IDK how one would ever know that.

 

[nabatron]

Yes, 87, sometimes it is listed at 88 as some gas stations. But no knock, no issues. I remember a poster here that mentioned in a thread someone he knew well (may have been a family member) who works for GM, said that premium isn't needed in these 6.2's. I believe in that post, the person who works for GM said you might get 20 more horsepower from premium but otherwise no real benefit or risk using regular. Can't remember the thread the post was in however.

I think I put two tanks of premium in my 23 AT4X, and honestly didn't notice any difference. I did actually listened for knocks, etc, with premium vs regular, and never noticed any difference.

Most likely, long term, premium is better for the engine. I just can't bring myself to spend 10 bucks or so more a tank for premium. Maybe it will bite me in the arse down the line.... although IDK how one would ever know that.

I mean if for some reason the engine blew up or whatever only way GM would know I guess would to tear down the engine and test the gas? Seems like a huge pain in the ass to do on their part but who knows. Shit now I’m on the fence between gas or diesel lol I’m weighing out pros and cons. I’m not going to tow anything and pretty much just want the diesel for mpg. Also would want to upgrade things on it for it to last. Like ppe oil pan, tranny pan, banks idash. Where as with the 6.2 just would have to worry about putting gas in and that’s about it lol

 

[Andystoy AT4]

I don't believe that any upgrades are necessary on the LZO to make it last, its only a 3L engine and holds 7 quarts of oil, the transmission is sealed so no dipstick, and the ECM controls transmission temperature via the 2 way valve. The air intake is a cold air intake in stock form and there is no muffler so its free flowing after the catalytic converter. There are enough miles on these engines that the LZO has the upgrades that GM thought were needed. The I Dash is useful for monitoring things like regen, oil temps etc. that the ECM monitors but are not displayed on the DIC.

IMO there is no free lunch with the 6.2 engine as far as octane of fuel recommended or required. All engines built today have very good knock sensors that pull timing whenever they detect preignition. You will not hear preignition before the sensor does but that does not mean that the ECM hasn't reduced timing by as many degrees as is required to stay out of the knock range. Reduced timing means reduced performance and fuel economy. Will the engine run on lower octane fuel yes but not in its optimal range.

Bottom line is its your truck so you can run whatever fuel you want to or can buy, as well as any upgrades you think are necessary. JMO

 

[Bullhound]

I have a 22 AT4 refresh with the baby Duramax. I've got over 12k miles and no complaints except the tires roar a lot more than I expected. It came with the Goodyear MT's. I absolutely love the fuel mileage. The best fuel econmy over 25 miles is 39mpg and 50 miles is 36.9. I came from a 2017 F150 (5.0) and would barely get 350 miles to a 24 gal tank. I'm getting close to 600 miles or more on this 24 gal tank. Also, from what I can tell, a full tank of DEF goes about 5000 miles, give or take. I'm getting much better price per mile on this DSL then I did on the F150 gas burner for sure!

 

[AmPitBull]

I went from a 6.2l to the 3.0 LZO... After 10k miles, I cannot imagine EVER going back to a gas engine in a half-ton truck.
I still have a 6.2l in a Denali w/ 200k+ miles on it. So, I am not jaded when it comes to the gasser.

 

[Wakinvol]

I went from a 6.2l to the 3.0 LZO... After 10k miles, I cannot imagine EVER going back to a gas engine in a half-ton truck.
I still have a 6.2l in a Denali w/ 200k+ miles on it. So, I am not jaded when it comes to the gasser.

I would have to agree. Same here and I LOVE mine.

 

[Cocoabean]

That’s good to hear besides the minor emissions stuff. How’s the regen on the trucks? I’ll be doing mostly city and short trips to work. I know you have to do a long drive for the regen to burn off the soot.

The regens are fine. Its not that you need a long drive, it just wants to continue running until complete. I do quiet a bit of around town and commute driving and hardly notice regens. I can tell its in regen by the tone of the exhaust and smell if I have my windows down. As long as you get some 30+ mile trips in you'll be fine.

 

[nabatron]

The regens are fine. Its not that you need a long drive, it just wants to continue running until complete. I do quiet a bit of around town and commute driving and hardly notice regens. I can tell its in regen by the tone of the exhaust and smell if I have my windows down. As long as you get some 30+ mile trips in you'll be fine.

For regens can you just let it sit in your driveway if you don’t make the full regen? Or do you have to be driving for it to do the full cycle?

 

[nabatron]

I went from a 6.2l to the 3.0 LZO... After 10k miles, I cannot imagine EVER going back to a gas engine in a half-ton truck.
I still have a 6.2l in a Denali w/ 200k+ miles on it. So, I am not jaded when it comes to the gasser.

I literally tried test drove them back to back. 6.2 first and then LZ0. The 6.2 was raw power and you could tell it was a v8. While the diesel was super smooth power band and felt really refined. I was impressed how smooth and quiet the diesel was.

 

[nabatron]

I don't believe that any upgrades are necessary on the LZO to make it last, its only a 3L engine and holds 7 quarts of oil, the transmission is sealed so no dipstick, and the ECM controls transmission temperature via the 2 way valve. The air intake is a cold air intake in stock form and there is no muffler so its free flowing after the catalytic converter. There are enough miles on these engines that the LZO has the upgrades that GM thought were needed. The I Dash is useful for monitoring things like regen, oil temps etc. that the ECM monitors but are not displayed on the DIC.

IMO there is no free lunch with the 6.2 engine as far as octane of fuel recommended or required. All engines built today have very good knock sensors that pull timing whenever they detect preignition. You will not hear preignition before the sensor does but that does not mean that the ECM hasn't reduced timing by as many degrees as is required to stay out of the knock range. Reduced timing means reduced performance and fuel economy. Will the engine run on lower octane fuel yes but not in its optimal range.

Bottom line is its your truck so you can run whatever fuel you want to or can buy, as well as any upgrades you think are necessary. JMO

With ppe they have a bigger oil pan that can hold 2 more quarts of oil. I mean that would help with engine life no? Mind you it will help with longer oil changes. Also you didn’t mention which engine you have?

 

[nabatron]

I have a 22 AT4 refresh with the baby Duramax. I've got over 12k miles and no complaints except the tires roar a lot more than I expected. It came with the Goodyear MT's. I absolutely love the fuel mileage. The best fuel econmy over 25 miles is 39mpg and 50 miles is 36.9. I came from a 2017 F150 (5.0) and would barely get 350 miles to a 24 gal tank. I'm getting close to 600 miles or more on this 24 gal tank. Also, from what I can tell, a full tank of DEF goes about 5000 miles, give or take. I'm getting much better price per mile on this DSL then I did on the F150 gas burner for sure!

Yeah those are unreal numbers for sure. With my hemi I have the bigger gas tank and it cost around $160-180 to fill up on regular. Roughly get 12-14mpg on a 2 inch lift on winters and gets worse when I put on my 35s. DEF to me wouldn’t really make a huge difference in cost since I won’t be towing and should last quite a bit