Why Do We Really Use EGR? [E191] - Diagnosing the Aftermarket A to Z

About this episode

Thanks to our Partner, NAPA Autotech TrainingIn this technical deep-dive, Matt Fanslow tackles the misconceptions surrounding Exhaust Gas Recirculation (EGR) in modern engines. Far from just a NOx-reduction tool, EGR plays a critical role in thermal efficiency, throttling losses, and combustion control. Matt dismantles common myths (like "lean burns hotter") and explains why engineers use EGR—even as technology evolves.Key Topics CoveredEGR’s Real PurposeBeyond NOx reduction: How inert exhaust gases slow flame fronts, improve thermal efficiency, and reduce throttling losses.Why lean air/fuel ratios don’t burn hotter—but can still cook exhaust valves.Throttling Losses & EfficiencyHow EGR allows wider throttle openings, reducing engine workload and boosting fuel economy.The link between EGR, Atkinson/Miller cycles, and extended combustion push.Internal EGR & Valve TimingModern engines use cam phasing to trap exhaust gases, creating insulating "pockets" that reduce heat loss to cylinder walls.SAE paper highlights: HCCI engines, controlled auto-ignition, and residual gas effects.Why This Matters for TechniciansUnderstanding EGR helps diagnose drivability issues, software updates, and emission failures.Matt’s rabbit-hole warning: Complexity is growing, but so are diagnostic opportunities.Notable Quotes"Lean air/fuel ratios burn longer, not hotter—that’s why exhaust valves fry.""EGR isn’t just about emissions; it’s about making the engine work smarter, not harder.""The more you know why engineers do something, the better you’ll diagnose it."Resources & ReferencesSAE Papers (Available at sae.org):Lean Burn SI Engines: NOx Control via Air/Fuel Ratio Modulation (2017)Impact of Valve Timing on Cold Start Emissions in GDI Engines (2019)Effects of Valve Timing on Residual Gas, Combustion, and Heat Transfer (2009)Thanks to our Partner, NAPA Autotech TrainingNAPA Autotech’s team of ASE Master Certified Instructors are conducting over 1,200 classes covering 28 automotive topics. To see a selection, go to napaautotech.com for more details.Contact InformationEmail Matt: mattfanslowpodcast@gmail.comDiagnosing the Aftermarket A - Z YouTube Channel Subscribe & Review: Loved this episode? Leave a 5-star review on Apple Podcasts and SpotifyThe Aftermarket Radio Network: https://aftermarketradionetwork.com/Remarkable Results Radio Podcast with Carm Capriotto: Advancing the Aftermarket by Facilitating Wisdom Through Story Telling and Open Discussion. https://remarkableresults.biz/Diagnosing the Aftermarket A to Z with Matt Fanslow: From Diagnostics to Metallica and Mental Health, Matt Fanslow is Lifting the Hood on Life. https://mattfanslow.captivate.fm/Business by the Numbers with Hunt Demarest: Understand the Numbers of Your Business with CPA Hunt Demarest. https://huntdemarest.captivate.fm/The Auto Repair Marketing Podcast with Kim and Brian Walker: Marketing Experts Brian & Kim Walker Work with Shop Owners to Take it to the Next Level. https://autorepairmarketing.captivate.fm/The Weekly Blitz with Chris Cotton: Weekly Inspiration with Business Coach Chris Cotton from AutoFix - Auto Shop Coaching. https://chriscotton.captivate.fm/Speak Up! Effective Communication with Craig O'Neill: Develop Interpersonal and Professional Communication Skills when Speaking to Audiences of Any Size. https://craigoneill.captivate.fm/