Crawford Dual Chamber AOS Review: Is It Worth It?

For those who push their Subaru on the track, at autocross events, or on winding backroads, engine protection is not optional. Under high G-forces and aggressive acceleration, your engine produces significantly more blow-by, putting it at risk of oil contamination and detonation. You need an Air-Oil Separator that can handle the abuse. This is where the engineering behind a part truly matters. This in-depth Crawford dual chamber AOS review examines its performance under the most demanding conditions, answering the critical question: does it keep your intake clean when it matters most? This is a must-read for any serious performance enthusiast.

Key Takeaways

• Preserve Engine Health and Performance: An Air-Oil Separator is a crucial defense for your Subaru's engine, stopping oily blow-by from contaminating the intake system, which prevents power loss and potential engine knock.
• Invest in a Maintenance-Free Design: Unlike a catch can that needs emptying, the Crawford AOS is a true "set it and forget it" solution; its integrated heater prevents sludge buildup and its automatic drain returns oil to the engine, ensuring constant protection.
• Prioritize an AOS for Aggressive Driving: If you enjoy track days, autocross, or spirited driving, an AOS is not optional, it is essential; it provides consistent oil separation under high G-forces and heavy engine load when your Subaru needs protection the most.

What Is an Air-Oil Separator and Why Does Your Subaru Need One?

An Air-Oil Separator (AOS) is one of the most important performance parts you can install on your Subaru, especially if it has a turbocharged boxer engine. Think of it as a guardian for your engine’s health. Its job is to intercept the oily vapor, known as blow-by, that escapes from the crankcase before it can get into your engine’s intake system. An AOS catches this blow-by, separates the oil from the air, and sends only clean air back into your engine. The separated oil goes back into your engine's oil pan where it belongs.

This simple process is critical for maintaining long-term performance and reliability. By keeping oil out of the intake, an AOS prevents a whole host of problems that can reduce power and even lead to engine damage. Whether you have a daily driven WRX, a track-prepped STI, or an overlanding Crosstrek, managing blow-by is key to getting the most out of your Subaru. It’s not just a modification for race cars; it’s a smart investment for any owner who cares about engine longevity.

Understanding Blow-By in Turbocharged Engines

So, what exactly is this "blow-by" we're talking about? In any engine, a small amount of combustion gases and unburnt fuel leaks past the piston rings into the crankcase. In turbocharged Subaru engines, this process is more pronounced, creating an oily mist. This oily mist can gum up parts like your intake manifold, valves, and intercooler, making them less efficient. Over time, this buildup can restrict airflow and hurt your engine's performance.

More importantly, when that oil vapor mixes with the incoming air and fuel, it lowers the fuel's octane rating. This contamination can lead to "engine knock" (detonation), which can seriously damage your engine's internal components. An AOS directly addresses this by cleaning the air before it re-enters the combustion chamber, ensuring your engine runs on pure, high-octane fuel and air.

AOS vs. Catch Can: What's the Difference?

When looking for a solution to blow-by, you’ll often see two options: an Air-Oil Separator and a catch can. While they serve a similar purpose, they operate very differently. A catch can is a simple reservoir that "catches" the oil vapor, which then condenses inside the can. The downside is that you have to manually empty it. If you forget, it can overflow and send all that collected gunk right back into your engine.

An AOS is a smarter, "closed-loop" system. It separates the oil and then automatically drains it back into your engine. This means you don't have to empty it, making it a "set it and forget it" solution for your Subaru WRX. This automated process ensures your engine is always protected without requiring constant maintenance, giving you total peace of mind.

Breaking Down the Crawford Dual Chamber AOS

The Crawford Dual Chamber AOS isn't just another part; it's a purpose-built solution designed to address the specific challenges of Subaru's boxer engine. Its design stands out because it tackles oil separation with a multi-faceted approach. Instead of just catching oil, it actively separates it and ensures the system works flawlessly in any condition. Let's look at the three core features that make this one of the most effective performance parts you can install.

The Dual-Chamber Advantage

At the heart of the Crawford AOS is its unique dual-chamber system. This isn't just a simple can; it's an intricate separator crafted from strong, aerospace-grade aluminum. The first chamber works to slow down the air charge coming from the crankcase, allowing heavier oil droplets to fall out of suspension. The air then moves to a second chamber for a final round of separation, ensuring only the cleanest air re-enters your intake. This design is incredibly effective at its job, protecting your engine by keeping unwanted oil out of the combustion process.

Why the Built-In Heater Is a Game Changer

One of the most critical features of the Crawford AOS is its integrated heater. In cooler temperatures, condensation can mix with oil vapor to create a thick, milky sludge that can clog lines and render an AOS useless. The Crawford AOS solves this by using engine coolant to heat the entire unit. This built-in heater prevents harmful residue from forming, ensuring the system functions perfectly year-round, from cold starts to hot track days. It’s a game-changing feature that guarantees consistent performance and reliability, no matter the climate.

The Benefit of an Automatic Oil Drain

The Crawford AOS is a true set-it-and-forget-it solution, thanks to its automatic oil drain. The system is designed to capture blow-by gases, efficiently separate the oil from the air, and route the collected oil directly back into the engine's oil pan. This means you never have to worry about manually draining a catch can or checking fluid levels. It creates a closed-loop system that keeps your engine protected without adding another maintenance task to your list, making it a practical upgrade for any Subaru WRX or STI owner.

Key Benefits of the Crawford AOS

Installing a high-quality Air-Oil Separator is one of the smartest moves you can make for your Subaru’s long-term health and performance. The Crawford Dual Chamber AOS isn't just another part; it's a comprehensive solution designed to address the inherent challenges of turbocharged boxer engines. From keeping your intake spotless to protecting your engine during aggressive driving, the benefits are tangible and immediate. Let's look at exactly what you gain by adding one to your build.

Prevent Carbon Buildup and Keep Your Intake Clean

Every time you drive your Subaru, especially under load, your engine produces blow-by. This is a mix of oil vapor, unburnt fuel, and exhaust gases that slips past the piston rings. Without an AOS, this oily mist gets recirculated directly into your intake system, coating your intercooler, intake manifold, and valves with gunk. The Crawford AOS intercepts this blow-by, using its dual-chamber design to separate the oil from the air. It then sends clean, dry air back into your engine while the collected oil is safely returned to the oil pan. This process is crucial for preventing performance-robbing carbon buildup and keeping your entire intake tract clean, just like it was from the factory.

Reduce Oil Consumption and Engine Knock

When oil vapor enters your combustion chamber, it gets burned along with the air-fuel mixture. This not only leads to increased oil consumption over time but also effectively lowers your fuel's octane rating. A lower octane level makes your engine more susceptible to detonation, or engine knock, which can cause catastrophic damage. By ensuring only clean air re-enters your intake, the Crawford AOS helps maintain your fuel's intended octane and prevents oil from being unnecessarily consumed. This is a critical step for anyone looking to protect their engine, especially if you're considering professional engine tuning services where consistent performance is key.

Enjoy Maintenance-Free Operation

One of the biggest advantages of the Crawford AOS is its self-draining, maintenance-free design. Unlike a traditional catch can that you have to manually empty every few hundred or thousand miles, the Crawford AOS automatically drains the separated oil back into your engine. This means you can install it and essentially forget about it. There are no cans to check, no hoses to drain, and no mess to clean up. This "set it and forget it" functionality is a core difference in the air oil separator vs catch can debate, giving you total peace of mind while ensuring your engine is always protected.

Protect Your Engine During Hard Driving

If you enjoy spirited driving, track days, or autocross events, an AOS is not just a recommendation; it's essential. During high-G cornering and aggressive acceleration, the oil in your engine sloshes around, increasing the amount of blow-by produced. The Crawford AOS is engineered to handle these extreme conditions, providing consistent and reliable separation when your engine needs it most. Forum users and track veterans agree that it provides invaluable peace of mind, knowing your engine is shielded from oil contamination and potential knock. It’s a smart investment that protects the heart of your car, making it a must-have for any serious Subaru WRX upgrades.

Crawford vs. IAG vs. GrimmSpeed: An Honest Comparison

When you start looking for an Air-Oil Separator, you’ll quickly find three names come up again and again: Crawford Performance, IAG Performance, and GrimmSpeed. All three are respected brands in the Subaru community, but their AOS designs have key differences in performance, quality, and intended use. Making the right choice depends entirely on how you drive your car and what you expect from your performance parts.

Let's break down how they stack up in the areas that matter most, so you can feel confident you're making the best investment for your engine. We'll look at real-world feedback and design principles to see which AOS truly delivers when it's put to the test.

Comparing Performance and Efficiency

The single most important job of an AOS is to keep oil out of your intake and turbo. On this point, the differences are clear. In a side-by-side review on the IWSTi forums, a user tested both the Crawford and GrimmSpeed units during autocross events. After two events with the Crawford AOS, they found only tiny traces of oil in the breather lines, and the hose leading to the turbo was completely clean. However, with the GrimmSpeed AOS, oil started building up in the turbo inlet hose after just one or two events. This shows that under the stress of performance driving, the Crawford design provides superior oil separation, directly protecting your engine's most critical components.

Build Quality and Materials

You want parts that are built to last, and the materials used in an AOS tell you a lot about its durability and effectiveness. The Crawford AOS is machined from aerospace-grade aluminum and features a unique dual-chamber design that is central to its efficiency. This isn't just a can; it's an engineered solution. In contrast, some users have described other options as feeling like a "band-aid" fix. When you're investing in protecting your engine, you want a robust, permanent solution, not a temporary patch. The quality of our performance parts reflects an engineering-first approach, ensuring every component is built for longevity and reliability under pressure.

Price and Overall Value

It’s true that the Crawford AOS often comes with a higher price tag than some competitors. But it's important to look at the overall value, not just the initial cost. As the forum review noted, the "more expensive Crawford unit" performed much better for demanding use. Think of it as an insurance policy for your engine. Paying a little more upfront for a part that effectively prevents oil contamination can save you from thousands of dollars in potential repairs related to carbon buildup, detonation, and premature wear. The consensus among enthusiasts is clear: "If you drive hard at all, the Crawford is a safer bet."

Which AOS Is Best for Aggressive Driving?

This is where the decision becomes simple. If you push your Subaru on the track, at autocross events, or even during spirited backroad drives, you need an AOS that can keep up. Forum discussions and user reviews consistently show that the Crawford AOS excels in all driving conditions, especially aggressive motorsports. It effectively keeps oil out of the intake system when the engine is under heavy load. In contrast, many have found that other systems struggle under high horsepower or hard driving. For a daily driver that rarely sees high RPMs, other options might suffice. But for the enthusiast building a high-performance Subaru WRX or STI, the Crawford AOS is the only choice engineered to handle that abuse.

What to Expect During Installation

So, you’ve decided to add a Crawford AOS to your Subaru. Great choice. The installation is a manageable project that you can tackle in your garage, but there are a few key details you’ll want to get right. Proper installation ensures the AOS functions exactly as designed, protecting your engine from oil blow-by and carbon buildup for years to come. Below, we’ll walk through the process, from the tools you’ll need to common challenges you might encounter, so you can feel confident whether you decide to do it yourself or hand it over to a pro.

Tools, Time, and Difficulty

One of the best parts about this upgrade is its straightforward installation. Most owners with basic mechanical skills can complete the job in about one to two hours. The Crawford AOS kit comes with all the high-quality hoses, clamps, and brackets you need, so you won’t be making extra trips to the auto parts store. Because our design includes a built-in heater that connects to your engine’s coolant lines, there is a bit more tubing to manage than with a simple catch can, but it’s a small price to pay for maintenance-free operation. You’ll just need a standard set of hand tools to get it done.

Getting Mounting and Hose Routing Right

Proper placement and hose routing are critical for your AOS to work correctly. The most important rule is to ensure the hose running from the AOS back to the PCV valve maintains a continuous downward slope. This allows the separated oil to drain back into the engine crankcase using gravity. If you create a low spot or "U" in the line, oil can pool there instead of returning to the engine. Also, be mindful not to pinch any hoses during installation, especially if you have a large top-mount intercooler that limits space in the engine bay.

Solve Common Installation Challenges

While the install is generally smooth, a few model-specific quirks and common mistakes are worth noting. For example, some 2010–2012 Subaru models have a large plastic intake manifold that can make mounting the AOS bracket a bit tricky, sometimes requiring a creative solution. A couple of common oversights include forgetting to plug the radiator fans back in after making space and not properly bleeding air from the coolant system. Our kits include robust performance parts to avoid issues, but taking your time and double-checking your work is always the best approach.

DIY vs. Professional Install: Which Is for You?

Should you install it yourself or take it to a shop? If you’re comfortable working on your car and have a couple of hours to spare, this is a very rewarding DIY project. However, if you’re new to engine modifications or simply want the peace of mind that comes with a flawless installation, there’s no shame in letting a professional handle it. A qualified technician can ensure every hose is perfectly routed and the system is bled correctly. If you’re looking for an expert touch, our team offers precision engine tuning services and installations.

Will the Crawford AOS Fit Your Subaru?

Before you invest in a critical engine component like an Air Oil Separator, you need to be certain it fits your specific Subaru. Fitment can vary based on your model, year, and even trim level, so getting it right from the start saves you time, money, and a lot of frustration. Here’s how you can confirm that the Crawford Dual Chamber AOS is the perfect match for your car.

Model and Year Compatibility (2002-Present)

The Crawford Dual Chamber AOS is engineered for a broad spectrum of Subaru models, covering vehicles from 2002 to the present. Whether you drive a track-ready WRX, a rugged Crosstrek, or a daily-driven Forester, there is likely a compatible AOS for your build. Our design accommodates various generations, including newer vehicles like the 5th generation Outback and specific 4th generation models. While the fitment is extensive, it's always a good practice to verify compatibility for your exact year, as small changes between model years can affect installation. You can browse our full catalog of performance parts to see the options available for your platform.

How to Confirm Fitment for Your Trim

The single best way to guarantee the Crawford AOS will fit your vehicle is to confirm it with our team directly. Different trim levels can have unique engine bay layouts or component variations, and we can provide precise information for your specific car. Another helpful step is to inspect your Positive Crankcase Ventilation (PCV) system. If you find the PCV tube is coated in oil, it’s a clear sign that your engine is experiencing blow-by and would benefit from an AOS. Once you've confirmed fitment, you can explore our complete line of Subaru WRX upgrades and other model-specific parts to complete your build.

Is the Crawford Dual Chamber AOS Worth It?

So, you've seen the specs and understand the benefits, but the big question remains: is the Crawford Dual Chamber AOS the right investment for your Subaru? The answer really depends on how you drive. Whether you're a weekend warrior hitting the track or a daily driver who just wants a healthier engine, the value of an AOS changes. Let's break down who benefits most from this upgrade and who might be able to hold off.

For Track Days and Autocross

If you push your Subaru to its limits on the track or at autocross events, the Crawford AOS isn't just a good idea; it's essential. During aggressive driving with high G-forces and tight turns, your engine experiences significant blow-by. The Crawford AOS is designed to handle these exact conditions, performing reliably when you need it most. Forum users and racers report that after intense track sessions, they find only minimal traces of oil in the breather lines, and the hose leading to the turbo remains completely clean. This proves the AOS is doing its job by preventing oil from contaminating your intake and lowering your fuel's octane. For any high-power build or aggressive driving style, this is one of the most important performance parts you can install.

For Daily Driving and Street Performance

You don't have to be a track star to benefit from an AOS. Think of it as a foundational upgrade for any turbocharged Subaru, whether it's stock or modified. For daily drivers, the Crawford AOS helps your engine run at its best by preventing the oil contamination that can lead to engine knock and reduced power. While it's an upfront investment, it's far more affordable than dealing with a damaged engine down the road. By keeping your intake system clean and maintaining optimal combustion, you're investing in the long-term health and reliability of your engine. It’s a smart move for anyone who cares about getting consistent performance from their Subaru WRX or STI on the street.

When You Might Not Need an AOS

Let's be honest, an AOS isn't a mandatory part for every single Subaru owner. If you primarily use your car for casual commuting and never push it hard, you might not see a significant benefit. An AOS is a preventative measure against the stresses of high-performance driving, not a fix for pre-existing oil consumption problems. However, the moment you decide to add more power or take your car to its first track day, the equation changes. If you're planning on engine tuning services or other modifications, an AOS becomes a must-have to protect your engine from the increased stress. It’s all about matching your upgrades to your driving ambitions.

Where to Get Your Crawford Dual Chamber AOS

Once you’ve decided the Crawford Dual Chamber AOS is the right upgrade for your Subaru, the next step is sourcing the part. The most reliable place to buy is directly from the official Crawford Performance website. Purchasing from us ensures you receive a genuine product, get the latest version, and have direct access to our expert support team for any questions about compatibility or installation. It’s the surest way to get the correct part for your build and avoid the risk of counterfeit products.

Beyond our official site, you can often find Crawford Performance products through authorized automotive retailers and performance shops. If you have a trusted local shop or a preferred online retailer for Subaru parts, check to see if they carry the AOS. Members on community platforms like the Subaru Outback Forums often share where they sourced their parts, which can be a great resource for finding a reputable seller with competitive pricing.

Before you finalize your purchase, it helps to have a budget in mind. Prices for the Crawford Dual Chamber AOS typically range from $250 to $450, though this can vary based on the retailer and any ongoing promotions. I always recommend reading through recent customer reviews and feedback on forums or product pages. Hearing from other Subaru owners who have already installed the AOS provides valuable insight into its real-world performance and helps you feel confident in your decision.

Related Articles

• Subaru 2.0 Air Oil Separator: The Ultimate Guide
• Subaru Air Oil Separator: The Ultimate Buyers Guide

Frequently Asked Questions

Do I really need an AOS if my Subaru is my daily driver and isn't modified? Think of it as a long-term investment in your engine’s health. Even a stock, daily-driven turbocharged Subaru produces blow-by. Over thousands of miles, that oily vapor will still coat your intake system, slowly reducing performance and efficiency. Installing an AOS is a preventative measure that keeps your engine running cleanly from the start, helping you avoid potential issues with carbon buildup and detonation down the road.

Why is the Crawford AOS more expensive than a simple catch can? You are paying for a complete, automated system, not just a simple container. A catch can is a passive device that you must manually empty, and if you forget, it can overflow and cause the very problem you're trying to prevent. The Crawford AOS is an active, closed-loop system that separates the oil and automatically drains it back into the engine. Its integrated heater also prevents sludge buildup in cold weather, ensuring it works reliably year-round without any maintenance from you.

Will installing an AOS void my Subaru's warranty? This is a common concern with any aftermarket part. Legally, a manufacturer cannot void your warranty simply because you installed an aftermarket component. They must prove that the specific part you installed directly caused the failure for which you are seeking warranty coverage. Since an AOS is designed to protect your engine from oil contamination and detonation, it actually helps prevent the kind of damage that could lead to a warranty claim in the first place.

What happens if I don't install an AOS on my turbocharged Subaru? Without an AOS, the oily blow-by from your crankcase gets recirculated directly into your engine's intake. Over time, this vapor coats your intercooler, intake manifold, and valves with a layer of gunk, restricting airflow and hurting performance. More critically, when that oil mixes with your fuel and air, it lowers the octane rating, which makes your engine more vulnerable to detonation (engine knock), a condition that can cause serious internal damage.

I've seen other AOS brands. What makes the Crawford design stand out? Our design is purpose-built to solve the specific challenges of the Subaru boxer engine. The two key features are the dual-chamber separation system and the integrated coolant heater. The dual chambers provide a highly effective, multi-stage process to remove oil from the air. The heater uses engine coolant to keep the entire unit warm, which prevents the oil vapor and condensation from forming a thick sludge in cold weather, a common failure point for systems without this feature. This ensures the AOS functions perfectly in all climates and conditions.