Why I Switched from 0W20 to 5W30 in My 3.0 Duramax — And What Oil Analysis Revealed
- Greg Nelson
- 3 hours ago
- 3 min read
When it comes to maintaining the longevity and performance of your 3.0L Duramax diesel engine, oil choice matters — a lot. While the owner's manual and oil cap clearly state that 0W20 is the recommended oil for this engine, real-world testing and used oil analysis (UOA) tell a deeper story.
In this post, I’ll walk you through my oil testing journey — how I went from 0W20 to 5W30, what the lab results revealed about engine wear, and why I'm now confidently running 5W30 in my own truck.
🛠️ The Factory Recommendation: 0W20
General Motors recommends 0W20 for the 3.0L Duramax (LM2 and LZ0) for a few reasons:
Optimized fuel economy
Cold-start flow behavior
Compliance with emissions systems
But there’s a tradeoff: 0W20 is very thin, and that might not always offer the best protection — especially under towing, heavy throttle, long trips, or high heat.
That’s why I turned to used oil analysis for answers.
🔍 What I Did
Instead of jumping straight into thicker oil, I ran a test series:
Ran several brands of 0W20 (Hot Shot’s Secret, AMSOIL, and Mobil 1)
Pulled used oil samples and sent them in for lab analysis
Compared wear metals, viscosity, oxidation, and fuel dilution
Switched to Pennzoil 5W30 and repeated the process
Bonus: A viewer submitted two samples of Schaeffer’s 0W20 for us to examine as well.
👉 You can view the full comparison of UOA results at: duramaxnews.com/oil-analysis
📊 0W20 Oil Analysis Breakdown
🧪 Hot Shot’s Secret 0W20
Iron: 47 ppm
Aluminum: 3 ppm
Copper: 7 ppm
Viscosity @ 100°C: 9.4 cSt
Decent, but iron was a little high. No engine flush was done between oil types, so results may be slightly skewed.
🧪 AMSOIL 0W20
Iron: 59 ppm (highest tested)
Viscosity: 8.6 cSt
Base Number: 2.31 (additive package was low)
Viscosity @ 100°C: 8.6 cSt
AMSOIL has a strong following, but these results weren’t promising.
🧪 Mobil 1 0W20
Iron: Better than AMSOIL @ 43 ppm
Oxidation: 30 (High result due to PAO/Ester Blend - Thanks Motor Oil Geek !)
Fuel Dilution: 2.8%
Viscosity: Lowest of the bunch
Not confidence-inspiring. Oxidation and fuel dilution levels were creeping into concern territory as reported by analysis lab but The Motor Oil Geek shared information on the video - "The Oxidation level of the Mobil 1 is due to it being a PAO/Ester blend. The result of 30 is normal for that oil. The 5W-30 is working better for these engines based on what we are seeing from these engines"
🔁 The Switch to 5W30 — Game Changer?
I decided to test Pennzoil 5W30, and the results were clear:
🧪 Pennzoil 5W30 (after 3,500 miles)
Iron: 26 ppm — lowest of all
Aluminum and Copper: Also decreased
Viscosity: 11.0 cSt
Oxidation: Stable
Fuel Dilution: Within normal range but still needs to be watched - possible injector issue or too much idling.
These results are a clear improvement. Lower wear metals and better stability made 5W30 a solid choice for my conditions.
🧾 What About Schaeffer’s?
Thanks to Karl (a viewer), we also got to review two UOAs from Schaeffer’s 0W20:
Iron: 48 ppm and 38 ppm
Copper: 12 and 11 ppm
Slightly higher iron and copper than my Pennzoil 5W30 sample. Even the lab recommended trying 5W30 to lower wear — assuming the additive package remains similar.
❓ Should You Run 5W30 in Your 3.0 Duramax?
By warranty, GM says 0W20. That’s what you’ll find on the oil cap and in the owner’s manual.
But if you’re considering making a switch, do it at your own risk:
Run UOA tests on your current oil first
Switch to 5W30 and compare wear metals
Don't mix oil brands unless you flush properly
Pay attention to iron, aluminum, copper, oxidation, and viscosity
For me, Pennzoil 5W30 outperformed all 0W20 options in real-world use. That doesn’t make it a one-size-fits-all answer — but it’s a step toward better engine protection.
📎 The Bottom Line
While 0W20 might meet EPA targets and offer cold-start performance, your engine might thank you for a slightly thicker option—especially if you’re towing, hauling, or keeping your truck long-term.
Data-driven decisions matter. That’s why I recommend using oil analysis before and after any switch.
👉 Want to compare oil reports? Visit the full UOA library on DuramaxNews.com
💬 Have questions or your own experience to share?
Drop a comment on the YouTube video or join the conversation on the site.
📺 Subscribe to DemonWorks on YouTube
Because the owner’s manual is just the start.