What are the negatives of oil catch can?

The negatives of oil catch cans include added cost, ongoing upkeep, potential disruption to the PCV system, risk of leaks, possible contamination of sensors, and mixed evidence on effectiveness depending on the vehicle. In short, they can create more problems than they solve if misapplied or poorly maintained.

Common drawbacks you should know

Before investing, consider these frequently cited downsides that can arise with oil catch cans:

• Added cost and ongoing maintenance: you buy the can, hoses, fittings, and you must regularly drain and clean it to prevent buildup.


• Potential for leaks and misrouting: a poorly installed system can leak crankcase oil or cause boost/vacuum leaks, which can trigger codes or rough idle.


• Impact on PCV system performance: if the can is too restrictive, it can raise crankcase pressure or alter the PCV flow, affecting engine breathing and seals.


• Sensor contamination risk: placing the can before the MAF or downstream of certain sensors can coat sensors with oil vapor, skewing readings and fuel trims.


• Oil mist in the intake: poorly baffled designs may still let oil droplets reach the intake, defeating the purpose or causing fouling elsewhere.


• Environmental and emissions considerations: venting to atmosphere (some versions) releases oil aerosols; this is not permitted in some regions and can violate regulations.


• Questionable performance gains: many engines do not show measurable improvements in horsepower or fuel economy, and carbon buildup on intake valves remains an issue for some engines.


• Compatibility and installation challenges: turbocharged engines, direct-injection systems, or cars with closed crankcase ventilation may require careful compatibility checks; a wrong fit can cause more harm than good.

These factors highlight why installation quality and engine type are decisive in whether a catch can is beneficial or problematic.

Engine design matters: when negatives bite hardest

Engine architecture and how the PCV/VVT/boost systems are integrated determine the risk profile of an OCC. Here are the angles to watch depending on your setup:

• Direct-injection and intake-valve carbon: in engines with direct injection, oil vapor still contributes to carbon buildup on intake valves; a catch can may reduce some oil carryover, but it is not a universal cure and the level of benefit varies widely.


• Turbocharged or supercharged engines: boosted engines place higher demands on the PCV path; a poorly rated catch can can become a restriction, causing crankcase pressure changes, leaks, or oil starvation in some configurations.


• Placing the can relative to sensors: if the catch can is installed upstream of the MAF sensor or in a sensitive air stream, oil films can foul the sensor and throw off air-fuel ratios.


• Vent type and emissions rules: many OEMs keep PCV systems sealed and reroute captured vapors back to the intake; some aftermarket cans vent to atmosphere, which can raise emissions and draw environmental concerns in certain jurisdictions.


• Maintenance and engine age: newer, well-maintained engines with clean PCV paths may see little or no benefit, while older engines with sludge buildup could see limited improvement yet require careful maintenance to avoid leaks.

In short, the negatives are more likely to materialize in engines where the PCV route is sensitive to restrictions or where sensors are vulnerable to oil vapor contamination.

Installation, maintenance, and reliability concerns

Even when a catch can is chosen with care, the practical realities of upkeep can be a pain point for many motorists. Consider these factors:

• Regular draining and cleaning: oil collects in the can, and if it isn’t emptied, it can back up into the PCV line or into the intake, causing smoke, odor, or performance issues.


• Quality and compatibility: cheaper cans with poor seals or low-grade hoses can leak or crack, especially under heat cycling or boost; compatibility with your engine’s PCV valve and vacuum lines is essential.


• Proper routing and orientation: incorrect hose routing can cause kinks, restrictions, or vacuum leaks; many manufacturers provide recommended routing diagrams—follow them closely.


• Installation risk: drilling or cutting into PCV hoses or manifolds can introduce leaks; if not confident, seek professional installation.


• Maintenance schedule: set a routine (e.g., every 4,000–6,000 miles) to inspect for leaks, check the fittings, and verify that the can is not blocked.


• Potential diagnostic confusion: if a problem arises (rough idle, codes, misfires), an OCC-related issue should be considered along with other common sources.

Adhering to manufacturer guidelines and selecting a high-quality, properly rated can minimizes these risks, but maintenance remains essential.

Myths vs. realities around oil catch cans

There are several popular beliefs about catch cans, but the practical impact depends on the specifics of the vehicle. The reality check below contrasts common myths with what the data and experience often show:

• Myth: A catch can eliminates all carbon buildup on intake valves. Reality: In engines with direct injection, oil vapor still contributes to deposits; a catch can may reduce some oil carryover but is not a universal fix for carbon buildup.


• Myth: They dramatically improve horsepower or fuel economy. Reality: Any gains are typically small or absent in many modern engines; improvements, if any, are highly engine-specific and often rely on other modifications.


• Myth: More expensive cans are always better. Reality: Quality matters (materials, seals, baffling) and installation matters more than price; a cheap unit poorly installed can cause leaks and sensor issues.


• Myth: OCCs are a universal solution for turbocharged engines. Reality: Some OEMs disallow modifying PCV lines, and the risk of leaks or sensor contamination can be higher; in many cases, OEM PCV design already handles crankcase ventilation well enough.


• Myth: They are maintenance-free. Reality: They require regular draining and cleaning; neglect leads to buildup and potential engine issues.

Owners should weigh claims against their engine type, driving style, and maintenance willingness before adding an OCC.

Summary

Oil catch cans can offer a modest reduction in oil vapor reaching the intake under certain conditions, but they come with tangible negatives: added cost, ongoing maintenance, potential to upset the PCV system or sensors, leaks, and mixed evidence of effectiveness. For many modern engines, especially those with well-designed OEM PCV systems or direct injection, the benefits are uncertain and the risks can outweigh them. Before installation, consult the vehicle manufacturer guidance, assess engine design and upgrade goals, and consider professional installation and regular maintenance to avoid common pitfalls. If you do proceed, monitor engine performance and emissions closely and be prepared to revert if problems arise.

Why don't manufacturers use oil catch cans?

The reason catch cans are not fitted to passenger vehicles is purely from a user experience. Most people don't even check their oil. So they would never empty their catch can. This would lead to a lot of issues when people start having problems and try to claim warranty.

Why are oil catch cans banned?

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 are the downsides of a catch can?

A filled oil catch can could reduce fuel efficiency, lower driving performance, or even damage the engine when the oil vapors aren't properly emitted.

Are oil catch cans bad for your engine?

An oil catch can is not inherently bad for an engine; however, a poorly designed, incorrectly installed, or poorly maintained catch can can cause problems. Issues arise when a catch can becomes clogged or is not emptied, which can lead to pressure buildup in the crankcase, potentially causing oil leaks or other engine damage. When installed correctly and maintained regularly by being emptied, an oil catch can can protect the engine by preventing oil vapors from entering the intake system, which keeps the intake and throttle plates cleaner.
 
This video explains how a clogged oil catch can cause engine problems: 59sAussie ArvosYouTube · Oct 1, 2022
Potential issues with oil catch cans 
This video demonstrates how an oil catch can collects oil and water vapor: 55sRepair GeekYouTube · Sep 22, 2024

• Clogging and pressure buildup: A catch can's filter can become clogged with oil, dirt, and moisture. If it is not emptied regularly, it can become full. This blockage can cause pressure to build up in the crankcase, which can force oil out of seals and gaskets, leading to leaks and potential engine damage. 
• Incorrect installation: Some catch can systems are designed to create a vacuum, which can be detrimental if the system is not correctly plumbed. A poorly designed system can also restrict the engine's Positive Crankcase Ventilation (PCV) system, leading to more issues than it solves. 
• Moisture and freezing: In cold climates, moisture collected in the catch can can freeze and block the system, causing a pressure buildup similar to a clogged filter. 

This video explains why oil catch cans are beneficial: 1mEngineering ExplainedYouTube · Apr 17, 2019
Benefits of a correctly functioning oil catch can

• Cleaner intake: It traps oil vapors that would otherwise get into the intake manifold, preventing carbon buildup on the intake valves and throttle body. 
• Reduced knock: By preventing oil from entering the intake charge, it helps maintain a cleaner fuel-air mix, which can reduce the risk of engine knock (detonation). 
• Improved engine longevity: By keeping contaminants out of the intake and combustion chamber, a catch can can help prolong engine life, especially for turbocharged or high-performance engines. 
• Pressure regulation: A properly functioning catch can can help manage crankcase pressure, which can improve piston ring sealing, horsepower, and fuel economy.