Episode 191

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Published on:

2nd Jul 2025

Why Do We Really Use EGR? [E191]

Thanks to our Partner, NAPA Autotech Training

In 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 Covered

EGR’s Real Purpose

  • Beyond 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 & Efficiency

  • How 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 Timing

  • Modern 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 Technicians

  • Understanding 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 & References

  • SAE 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 Training

NAPA 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 Information

The 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/

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About the Podcast

Automotive Field Theory
From Automotive Diagnostics to Metallica and Mental Health
Automotive Field Theory explores the forces that shape automotive repair, including the ones measured with a meter or oscilloscope and the ones that cannot be found on a wiring diagram.

Hosted by automotive diagnostic specialist, shop manager, and instructor Matt Fanslow, the podcast begins in the automotive aftermarket but rarely stays inside its traditional boundaries. Diagnostics, electricity, technology, leadership, psychology, economics, game theory, history, music, movies, family, and human behavior may appear unrelated. Look closely enough, however, and connections begin to emerge.

A vehicle may arrive with a technical fault, but the work surrounding it is rarely technical alone.

Information is incomplete.

People make decisions under pressure and uncertainty. Incentives shape behavior. Standards gradually drift. Good intentions produce unexpected results. The official process may say one thing while the system quietly rewards another.

Automotive Field Theory is an attempt to understand those interactions.

Drawing from real diagnostic work, shop management, industry conversations, personal experience, and an occasionally inconvenient level of curiosity, Matt examines not only how things work, but why they work that way, how they became what they are, and what apparently unrelated subjects might teach us about repairing vehicles, leading people, running businesses, and improving the automotive industry.

Some episodes begin with a failed component. Others begin with Metallica, quantum physics, professional wrestling, a historical disaster, a round of golf, or a question that refuses to leave Matt alone.

Eventually, they all enter the same field.