LZ0 vs LM2 - Holiday MPG update

SC4R3C120W · January 6

I went from a 2020 LM2 (2wd) to a 26 LZ0 (4wd) and have been enjoying it a lot. I commute 60 miles, 1-way to work (120 round trip) from Orange County to Los Angeles. In the morning it takes my roughly 1-hour, heading home 1hr 45min - 2.5hours. My previous normal average was 30 - 33 mpg in my LM2 (modded with 3" lift, 33" tires, and a few PPE tubes). With the new stock truck (no mods, 31" tires, and 4x4), I average 28mpg. With the holidays, colder temps, and less traffic, I now jumped up to 30mpg. I use a fuel tracker and can confirm that the numbers on the dash are typically spot on with the actual driving.

Another thing I noticed, and maybe because it's new, but the DEF usage is much less. My background with DEF is, and is my opinion, that is is corrosive and crystalizes easily. Also being an emissions item, I don't like being less than half a tank. I figure with the heaters in the def tank and the way it can crystalize, I always want it full. Plus, when I get down to half a tank of DEF, it takes a single 2.5 gallon box. No over filling and spilling, no filling and realize you need more for full. My LM2 went about 2000-3000miles to a half tank (one box), and my first fill up in the LZ0 was 3770 miles. I hope this continues.

Below are some pics of the screen and mileage app

Atlas · January 7

Good info.

My truck was delivered with the DEF tank just under half full. Truck only had something like 30 miles on it so it was probably that way from the factory. Long story short, I didn't care. Threw in a 2.5 gallon jug of DEF when I got home and that brought it up to completely full. That's when I found out the capacity of the tank is probably ~5 gallons.

In 1500 miles of driving... The truck didn't see highway speeds for literally the first 500 miles. It didn't tow anything until just after 1,000 miles. The last 400 miles were towing a loaded trailer between 6k-7k lbs depending on the car that was on it. The DEF gauge has lost one bar in 1500 miles of driving so far.

I am thinking the DEF usage complaints are definitely limited to the LM2. The 2025+ LZ0 seems to consume DEF very slowly.

StingerZ16 · January 7

2 hours ago, Atlas said:

LZ0 seems to consume DEF very slowly.

That seems true. Until you start towing.

I now carry a box of DEF in truck when I am towing my travel trailer.

It seems to suck it down when towing. I have had to stop and get DEF once, just to get home.

Now, I just bring some with me.

BIGDOGx · January 9

Man i couldn't imagine owning a Fullsize truck in that god forsaken corrupt state!

Z45 · January 13

Some info that may be helpful on DEF etc...from GM service info....

The DEF level gauge does not operate like a typical float-style gauge that is used in a fuel tank. The Engine Control Module (ECM) monitors the DEF level and consumption rate in order to calculate an estimated range. DEF levels are detected by the DEF level sensor.

There may be some fluctuation in the amount of DEF represented on the DEF level gauge. After filling the DEF tank, it may take a few key cycles to register the correct amount in the DEF tank. With the new segmented DEF level gauge, it is possible that after adding 5 gallons (18.9 L) of DEF that the gauge reads as a full tank after the fill event. However, if the actual level of DEF is just entering the last segment on the gauge, the gauge is likely to drop by one segment shortly after driving after the fill event. As a result, a driver could have an initial impression that the vehicle consumes an excessive amount of DEF.

Emissions Requirements

Every year, GM produces diesel engines that continue to meet aggressive federal requirements to reduce Nitrogen Oxides (NOx) in the vehicle exhaust. As DEF is required to reduce the NOx in the exhaust, DEF consumption will increase as NOx reduction requirements increase. Customer trading in an older model year diesel vehicle for a newer model year vehicle will likely see an increase in DEF usage. DEF consumption increases as the newer vehicles meet the more stringent emission requirements for that model year.

The amount of DEF consumed also is a function of how hard the engine is working, or engine load. Due to engine use, it is more representative to compare DEF consumption to the amount of fuel consumed – also a function of engine load – instead of miles traveled. In addition to engine load, other factors that affect the DEF usage rate are the humidity, temperature, and altitude where the vehicle is operating.

Under certain conditions, the ECM will increase or decrease the amount of DEF used based on learning or adaptive algorithms. In the event of a malfunction and Check Engine light, the ECM may double or even eliminate the amount of DEF that is being used. An improper amount of DEF use will continue until the vehicle is repaired and the learned value in the ECM is reset.

– Thanks to Larry Yaw

N715DP · January 13

I thought I'd pop in here just for future reference as folks come across this thread. My data is related to the LM2. I bought my 22 (refreshed) in June of 2024 and for the first (roughly) six months, I tracked all of my fuel usage - sadly, I didn't with DEF but it's so minimal that it doesn't really matter. The google spreadsheet linked below are the results. The comparison was to real-world mileage of my final-year Chevrolet Avalanche with the 5.3 (I had the "displacement on demand" disabled because it was worthless and annoying).

https://docs.google.com/spreadsheets/d/1MKHG6HOO_osUZQHqQQuoGAeSveTb7jN0ePLnCsLUeVk/edit?usp=sharing

TL:DR, tracking cost per gallon of regular versus diesel and my driving experiences over that 6 monthly led to a roughly 30% "savings" compared to the 5.3. Obviously the cost of DEF and other factors such as fuel filter replacement would bring this down but those costs are so minimal, I didn't bother to factor them in. I will also note that I am a conservative driver, rarely speed more than a couple MPH over the limit with traffic flow. I don't "hyper mile" but I don't drive my truck like a sports car either.

Not sure if anyone cares, just thought I'd drop it here for anyone that happens upon this thread looking for information.