Will a catch can increase mpg?

In practice, a catch can does not reliably increase miles per gallon. Any mpg gain is typically small and depends on the engine, installation quality, and driving conditions. The device's main purpose is to trap oil vapor and reduce carbon buildup in the intake path, rather than to deliver a fuel economy boost.

How a PCV catch can works

Most modern engines use a positive crankcase ventilation (PCV) system that routes blow-by gas from the crankcase back into the intake to be burned. A catch can is an optional add-on that sits in the line between the PCV valve or valve cover and the intake, attempting to capture oil droplets and moisture before the vapors reach the engine. If designed and installed correctly, the can should not significantly restrict airflow; some designs vent to the intake again while others vent to the atmosphere. The key is to maintain a closed loop and to maintain proper vacuum in the PCV system.

Types and placement

There are several configurations, including inline cans between the valve cover and PCV valve, or between the PCV valve and the intake manifold. Some products vent to atmosphere; others keep the system closed with a check valve and a filter. For road-legal use in many places, a sealed, internal-filter catch can that returns vapors to the intake is preferred to minimize emissions and avoid leaks.

Impact on fuel economy

What matters for mpg is how the catch can affects airflow, engine breathing, and long-term cleanliness of intake passages. The following points summarize the current understanding:

• Direct impact on air flow: A high-quality, properly installed catch can should add negligible flow resistance, so immediate mpg change is typically minimal. Poor fitment or overly restrictive designs can reduce airflow and possibly lower mpg under some conditions.


• Carbon buildup and long-term efficiency: By trapping oil, a catch can can reduce carbon buildup on intake valves in some engines, which may help maintain efficiency over time. Any mpg benefits from this are usually small and accrue gradually with mileage.


• Emissions and regulations: Venting vapors to the atmosphere increases hydrocarbon emissions and can be illegal in many regions; a closed system is generally required for street use. Noncompliant setups won't improve emissions or mpg and can cause failures in inspections.


• Engine type and usage pattern: Turbocharged or high-blow-by engines may see more noticeable effects on long-term performance, but the immediate mpg improvement remains uncertain and highly variable associated with maintenance levels and driving style.


• Measurement and context: MPG is influenced by aerodynamics, tires, weather, and driving, which overshadow the tiny changes a catch can might cause.

In practice, drivers should not expect a reliable fuel economy gain from a catch can. The more tangible benefits are related to engine cleanliness, throttle response, and potential long-term maintenance costs avoidance, rather than a guaranteed mpg boost.

Practical considerations for installation

Before installing a catch can, consider the legal, maintenance, and performance implications. The following tips help ensure safety and reliability, rather than fuel economy gains:

• Choose a sealed, baffled catch can designed for automotive use, with a proper check valve and no venting to atmosphere in regions with strict emissions rules.


• Ensure correct routing: from the valve cover/PCV to the intake, avoiding vacuum leaks and ensuring the PCV valve's operation remains within manufacturer specifications.


• Regularly drain and inspect the can; a clogged can can impede crankcase ventilation and cause vacuum leaks or reduced engine performance.


• Monitor for leaks, odors, or check-engine warning lights after installation; if issues arise, revert to stock configuration or consult a professional.

In short, the catch can is a maintenance-oriented device rather than a guaranteed efficiency upgrade; if used, it should be part of a broader program of engine care and compliance with local regulations.

Summary

The catch can serves to manage crankcase vapors and help reduce intake carbon buildup, which can support long-term engine reliability. It is not a proven method to reliably increase miles per gallon, and any mpg gains are typically negligible and highly dependent on many variables. For most drivers, the cost and potential risk to emissions or drivability are not justified by expected fuel economy improvements. Emphasize proven efficiency practices alongside any catch can installation.

Why are oil catch cans illegal?

Oil catch cans can be illegal because they modify a vehicle's positive crankcase ventilation (PCV) system, which is part of the vehicle's emissions control system. Altering the PCV system is often illegal in states with strict emissions standards, such as California, as it can interfere with the reintroduction of crankcase fumes into the engine for proper combustion and emission control. Some catch cans that vent to the atmosphere are explicitly illegal because they release pollutants, while others may be non-compliant if they aren't installed correctly or don't meet local regulations.
 
This video explains why oil catch cans can be illegal in some areas and when they are compliant: 1mBig Truck Lovers YouTube · Aug 27, 2025
Reasons why oil catch cans can be illegal

• Tampering with emissions systems: Installing an oil catch can is considered a modification of the factory emissions system. The PCV system is designed to route crankcase fumes back into the engine to be burned, which reduces air pollution. 
• Venting to atmosphere: Many catch cans have an air filter that vents to the atmosphere, releasing pollutants and making them illegal in many areas with strict emissions laws. 
• Disrupting engine function: Some catch cans can alter the flow of air and pressure in the engine, potentially causing the engine to run less efficiently. 
• Visual inspection: During an emissions test, a visual inspection may identify the catch can as a non-compliant modification, leading to a failed inspection. 

When catch cans might be legal

• Closed-loop systems: Some catch cans are designed to be compliant because they maintain a closed-loop system by venting clean air back into the intake, but this requires specific, non-venting designs. 
• Local regulations: The legality varies greatly by location. Some states may allow them, while others, like California, have much stricter rules. 
• CARB-compliant models: If a model is specifically certified by the California Air Resources Board (CARB) and is installed correctly, it may be legal to use in California. 

You can watch this video to learn more about the effects of oil catch cans: 1mAuto Expert John CadoganYouTube · Jul 18, 2018

What upgrades increase MPG?

Air Intake Systems
One of the simplest ways to increase gas mileage is by installing an aftermarket air intake system. These systems are designed to allow more air to flow into the engine, which can result in improved combustion and better fuel efficiency. Some air intake systems can increase gas mileage by up to 5%.

Will a catch can improve MPG?

Oil catch cans don't directly improve fuel economy, but they do help by limiting engine wear and tear caused by knocking and pinging.

Do catch cans make a difference?

Oil catch cans are simple devices that can greatly benefit direct-injected engines. They prevent oil and other contaminants from causing buildup inside your engine's intake manifold.An oil catch can acts as a filter, plugging into this hose line to "catch" the contaminants before they can reach the intake.