2018 Chevrolet Colorado Spark Plug Replacement — 3.6L Gas vs. 2.8L Duramax Diesel

I've done the spark plugs on the 3.6L Colorado and it's a clean job once you know the layout. There's one important thing to address upfront: if you have the 2.8L Duramax diesel, you do not have spark plugs. Diesel engines ignite fuel through compression, not a spark. What you have are glow plugs — a completely different component. I'll cover both engines so you know exactly where you stand.

Which Engine Do You Have?

• 3.6L V6 (LGZ) — Natural gas engine. Six spark plugs. This guide covers the full procedure.
• 2.5L I-4 — Also gasoline. Four spark plugs. Similar procedure but different plug spec.
• 2.8L Duramax LWN diesel — Compression ignition. No spark plugs. Has 4 glow plugs instead.

3.6L LGZ V6 — Spark Plug Replacement

Parts and Specs

Item	Spec / Part Number
Spark plug	ACDelco 41-122 (iridium)
OEM GM equivalent	GM 12643659
Alternative	NGK 95770 (ILZKAR7D11)
Plug gap	Pre-gapped — do not adjust
Thread size	M14 × 1.25
Torque	15 ft-lb (20 Nm)
Interval	97,500 miles (iridium)
Socket size	5/8"

Tools Needed

5/8" spark plug socket, 3" / 6" / 10" extensions, wobble extension (helpful for rear bank), torque wrench, 10mm socket (COP bolts), compressed air, dielectric grease.

3.6L V6 Step-by-Step

Bank access: Front bank (cylinders 1, 3, 5) is accessible from the front. Rear bank (cylinders 2, 4, 6) is at the rear near the firewall — this is where you'll spend most of your time.

1. Let engine cool completely. Aluminum heads strip easily when warm.
2. Remove plastic engine cover — lifts off 4–6 mounting posts.
3. Remove front bank COPs (3 units): one 10mm bolt + connector each. Pull straight up.
4. Remove rear bank COPs (3 units): long extension needed for the 10mm bolts near the firewall.
5. Blow out all plug wells with compressed air before removing any plug.
6. Remove front plugs: 5/8" socket + 6" extension. Work one at a time.
7. Remove rear plugs: 5/8" socket + 10" extension + wobble joint. Take your time — forcing a misaligned plug in an aluminum head causes cross-threading.
8. Install ACDelco 41-122 plugs. Pre-gapped — do not adjust. Thread by hand until snug, torque to 15 ft-lb (20 Nm).
9. Apply dielectric grease inside each COP boot. Reinstall all 6 COPs, tighten 10mm bolts, reconnect connectors.
10. Replace engine cover. Start engine and monitor for misfire codes (P030X).

2.8L Duramax Diesel — Glow Plug Service

No spark plugs on this engine. It has 4 glow plugs (one per cylinder) that pre-heat the combustion chamber for cold starts.

Item	Spec
Glow plug	ACDelco 2100011
Torque	13 ft-lb (18 Nm)
Socket size	8mm hex

If the plugs have been in over 80,000 miles, apply penetrating oil the night before — diesel glow plugs seize in aluminum heads badly.

Common Mistakes

Installing rear bank plugs with a ratchet at an angle to the plug axis. Deep wells + wobble extension + limited swing room = easy to start threading cross-angle. If you feel any resistance threading by hand, stop and back the plug out. A cross-threaded plug in an aluminum head is a $300+ helicoil repair. Thread every plug by hand for at least 4–5 full rotations before putting a tool on it.

Pro Tips

• The 3.6L V6 rarely shows symptoms before plugs are fully worn — follow the 97,500-mile interval.
• For the diesel: if you have long cranking times in cold weather, check the glow plug relay and module before replacing the plugs — the relay fails more often.

Save Money with OwnerDrop

A dealer spark plug service on the 3.6L Colorado runs $200–$300. ACDelco 41-122 plugs cost about $10 each ($60 for 6). That's $140–$240 in savings for a 90-minute job.

For related Colorado maintenance, the 2015 Chevy Colorado brake pad replacement guide covers the front and rear brake procedure. The 2018 GMC Canyon oil change guide shares the same 2.8L Duramax platform service tips.

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