Do catalytic converters have an adverse affect on gas mileage or engine lifespan?

It would seem it takes extra energy to operate the chemical reactions occurring in a catalytic converter, thereby decreasing gas mileage and increasing stress/strain on the engine.

  • Short answer; no. Virtually every vehicle with electronic fuel injection is self-governing, regardless of catcon operation since the catcon uses platinum to react to exhaust gases, turning them into harmless byproducts; HC, CO and NO2. Fuel mileage relies on two things; decades of mechanical engineering resulting in software programming in every engine computer to operate engines, and your right foot. The catcon is strictly for emissions control to pollute less compared to non EFI engines without catcons. Best example; every muscle car engine producing hundreds of hp with clean exhaust.
    – F Dryer
    Nov 18, 2023 at 19:30

2 Answers 2


They create back pressure in the exhaust, which takes power (and corresponding amount of fuel) to overcome.

Other than that, no adverse effects I'm aware of.

  • Yeah, that's what I thought. And that back-pressure takes more energy to overcome; ergo, it would seem catalytic converters would reduce cars' fuel economy.
    – Geremia
    Nov 19, 2023 at 21:55

The chemical reactions in the exhaust system are caused by specific byproducts interacting with the catalyst embedded in the converter. A catalyst is a compound or a component which causes or assists in a reaction without being consumed.

There is no connection between fuel economy or engine lifespan and the converter, other than that the engineers responsible for designing and building the vehicle, specifically the engine, can take into allowance that some of the chemicals generated by combustion will be processed/eliminated in the converter.

As a result, it is likely that less effort is expended in an attempt to prevent these harmful compounds from entering the atmosphere. It is also likely that the results will allow the engineer to focus on fuel economy and engine longevity. The linked site goes into much detail and also notes that a failed converter will create back pressure which is going to adversely affect the engine performance. Image from a UK site:

catalytic converter


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