LM2 vs LZ0 Glow Plugs: Critical Differences You Must Know Before Replacing Them on Your 3.0 Duramax

Greg Nelson
50 minutes ago
3 min read

If you're planning to swap the glow plugs on your 3.0L Duramax diesel (whether it's in a Silverado, Sierra, Tahoe, Yukon, or Escalade), stop right there. The LM2 and LZ0 engines use completely different glow plugs — even though they look nearly identical at first glance. Mixing them up can send the wrong voltage through the system, leading to poor cold starts, damaged components, or even catastrophic engine failure.

In our latest video, we pulled both types apart, tested them, and showed exactly why you need to get this right.

LM2 Glow Plugs (73G) – First-Gen 3.0 Duramax

Part reference: 73G (often listed as GM 24000504 or ACDelco 73G)
Control: Uses a dedicated Glow Plug Control Module
Nominal voltage: 5.4 volts
Cold start sequence:
- 7.2 volts for 2.2 seconds
- Then 5.7 volts for 8 seconds
- Then 5.4 volts until reaching approximately 1200°C
Operating range (once running): 4.7–10 volts
Target temperature: 1150–1180°C

These plugs are single-use only. Anytime you remove a glow plug, it must be replaced with a new one. Early 2020 LM2 engines also came with a special 150,000-mile warranty policy on the #2 glow plug — check with your dealer to see if it still applies to your VIN.

LZ0 Glow Plugs (72G) – Updated 3.0 Duramax

Part reference: 72G (ACDelco 72G)
Control: No separate Glow Plug Control Module — now fully ECM-controlled
Cold start sequence:
- 11 volts for 2 seconds
Steady state: 7 volts to maintain 1100–1250°C

The LZ0 runs higher initial voltage and a simpler control strategy. This is a big reason why the two plugs are not interchangeable. Applying 11 volts to an LM2-style plug (or vice versa) can cause serious issues.

Both versions reach roughly the same operating temperatures, but they get there in very different ways.

Physical Differences – How to Tell Them Apart

Even though they look similar, close inspection reveals key differences:

Thread to head spacing
Tip design (LZ0 has a distinct step design)
Gap between threads and the body
Part numbers stamped on the plugs (though they can be hard to read)

Pro tip: Always compare the new plug to the one you removed, or check your exact engine code (LM2 or LZ0) before ordering.

Why These Glow Plugs Are Extremely Fragile (And How to Avoid Disaster)

These are ceramic-tipped glow plugs — not traditional metal ones. They are very delicate:

Never drop them. If you drop a new glow plug, replace it immediately. In the video, we dropped one on purpose — the ceramic tip popped right out.
New plugs often ship loose in the box with no protection. Gently pull on the tip to check that it’s secure before installation.
Always use a glow plug bore reamer before installing a new plug. Carbon and soot buildup from the old plug stays in the bore. Installing a fresh plug without cleaning can sideload the fragile ceramic tip and cause it to break off inside the cylinder — resulting in “kaboom” engine damage.

A good reamer (available on Amazon or from GM tool suppliers) is cheap insurance. The GM special tool is essentially identical to quality aftermarket versions. Glow Plug Reamer: https://amzn.to/4svvdvV - Amazon Affiliate Link

How to Test Glow Plugs Before Installation

We strongly recommend testing every glow plug with a multimeter before installing it:

Use alligator clips on the multimeter.
A good plug reads around 0.5 ohms.
An open circuit (infinite resistance) means the plug is bad — do not install it.

Testing only takes a minute and can prevent installing a faulty plug whose tip might fall into the combustion chamber.

Installation Tips

Torque spec: 150 inch-pounds (do not overtighten)
These are single-use only — never reuse a removed glow plug
Be gentle during handling and installation
Install dry, no lubrication on threads

Watch the Full Video

See the side-by-side comparison, voltage explanations on the whiteboard, bore reamer demo, multimeter testing, and the dramatic glow plug drop test:

[Watch the Video: LM2 vs LZ0 Glow Plugs – The Difference That Can Destroy Your 3.0 Duramax] https://youtu.be/kXbZNvF2Q5Y

Final Advice

Double-check whether your truck has the LM2 or LZ0 engine before buying glow plugs. Confirm the part number and visually compare if possible. Taking a few extra minutes to verify can save you from thousands of dollars in engine repairs.

Have you ever replaced glow plugs on your 3.0 Duramax? Did you run into any issues with the ceramic tips or identifying the correct part? Drop your experiences in the comments below.

Stay tuned to Duramax News for more in-depth maintenance, repair, and technical guides on the LM2 and LZ0 3.0L Duramax diesel.