How Does Upgrading the Exhaust Manifold Gasket to a Multi-Layer Steel (MLS) Version Improve Sealing in a Subaru STI?

March 26, 2024

As owners of Subaru vehicles, specifically the WRX STI model, you might have encountered the need to replace the gasket in your vehicle’s exhaust manifold. This crucial part plays a role in maintaining the efficient operation of your car’s engine, but its long-term performance can be improved by considering a particular kind of upgrade – the multi-layer steel (MLS) gasket. Initially, you may question the necessity of such a modification, but when its benefits are understood, it becomes clear that making this switch can enhance your vehicle’s function on various fronts. So, let’s dissect the MLS gasket and comprehend why it’s a preferred choice over the standard OEM gasket.

Understanding the Role of Gaskets in Your Subaru’s Engine

Before we delve into the specifics of the MLS gasket, it’s crucial to understand the role of gaskets in your Subaru’s engine. A gasket is essentially a seal, strategically positioned between the cylinder head and the engine block. It serves a dual purpose – to maintain a robust seal between these components and to inhibit the mixing of the engine’s oil and coolant.

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These components endure intense heat and pressure, and the gasket must effectively cope with this environment to maintain optimal engine performance. It’s crucial to note that a compromised gasket can lead to significant issues for your Subaru, including overheating and loss of compression, which can bring about costly repairs if not promptly addressed.

The Pitfalls of the OEM Gasket

We know that an OEM, or Original Equipment Manufacturer, gasket is the standard part installed in your Subaru STI during production. While these gaskets are designed to suit the specifications of your engine, they are not exempt from potential flaws.

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The OEM gasket is typically constructed of composite materials, which can be susceptible to breakdown under the harsh conditions within your engine. Common issues can include warping and leaking, which can lead to poor performance and potential engine damage. Furthermore, regular replacement of these gaskets can be costly over time, both in terms of parts and labor.

The Advantages of the MLS Gasket

Now, let’s consider the MLS gasket. Standing for Multi-Layer Steel, this kind of gasket is constructed from multiple layers of steel, with each layer serving a specific purpose. The outer layers are coated with a thin layer of rubber, which enhances the sealing properties of the gasket, while the middle layer is typically embossed to provide superior sealing around the combustion chamber.

This structure provides the MLS gasket with several advantages over an OEM gasket. For starters, the steel construction gives it superior durability, making it more resistant to the hard conditions within the engine. An MLS gasket can withstand higher temperatures and pressures without warping or degrading. This leads to longer intervals between replacements, saving you money in the long run.

How the MLS Gasket Improves Sealing in your Subaru STI

The primary advantage of the MLS gasket lies in its improved sealing capability. Thanks to its multi-layer design and the rubber coating on the outer layers, this gasket can form a tighter seal between the cylinder head and the engine block in your Subaru’s engine.

Better sealing results in improved engine performance. With a more robust seal, the risk of leakage is reduced, which can prevent loss of compression and stop the mixing of oil and coolant. Also, the superior durability of the MLS gasket means that the seal remains effective for a longer period, reducing the risk of issues related to gasket failure.

Reviews and Price Considerations

The shift to MLS gaskets has been well received by Subaru owners, and numerous online reviews attest to the improved performance and durability these gaskets provide. However, one must consider the initial price difference. While an MLS gasket is typically more expensive than an OEM one, the long-term benefits, such as reduced replacement frequency and improved engine performance, can offset the initial cost.

To conclude, the decision to upgrade to an MLS gasket for your Subaru STI should be viewed as an investment in the health and longevity of your vehicle’s engine. The superior sealing, durability, and performance of these gaskets make them a worthy consideration for any Subaru owner. As always, remember to consult with a trusted mechanic or specialist before making significant changes to your vehicle.

Compatibility and Installation of MLS Gaskets in Subaru Models

When considering an upgrade to the MLS gaskets in your Subaru WRX STI, one of the key aspects to contemplate is their compatibility and installation process. Most MLS gaskets are designed to be compatible with a range of Subaru models, including the popular Subaru Impreza and Subaru Forester. This makes them a practical choice for a wide variety of Subaru owners.

The installation of an MLS gasket requires professional hands due to its complex nature. While it may seem like a daunting task, it can be carried out efficiently by a qualified mechanic. The gasket is installed between the cylinder head and the exhaust manifold, and its multi-layer design allows it to adapt to the surface irregularities, providing a robust seal.

Furthermore, the MLS gaskets often come with a stainless steel fire ring. This ring is particularly useful in high-performance engines like the ones found in the WRX STI, as it provides an additional level of sealing around the combustion chamber. This ensures that exhaust gases are efficiently channeled away from the engine, further enhancing its performance.

Reviews Posted by Subaru Owners

The performance and reliability of MLS gaskets have been praised by a multitude of Subaru owners. Numerous Subaru drivers have reported a marked improvement in their engine’s performance and durability after upgrading to an MLS gasket.

Many reviews posted by satisfied customers cite the evident resistance to heat and pressure, and the resulting reduction in leaks and breakdowns. Users also appreciate the longevity offered by these gaskets, as it means fewer replacements and, consequently, less money spent on parts and labor.

The initial investment in an MLS gasket, although higher than an OEM one, seems to pay off over time. This is something that many Subaru owners have noticed and shared in their reviews. Despite the initial cost, they have found the long-term benefits and overall enhancement of their vehicle’s performance well worth the investment.


After a complete understanding of the intricacies of the MLS gasket, it’s clear that this upgrade offers substantial improvements to the sealing, durability, and overall performance of a Subaru’s engine. More than just a replacement for your standard OEM gasket, the MLS variant provides a range of benefits that can significantly enhance the operation and longevity of your vehicle.

Despite requiring a higher initial investment, the long-term advantages of the MLS gasket, including the decreased need for replacements and enhanced engine performance, make it a wise choice for the forward-thinking Subaru owner. From the Subaru Impreza to the Subaru Forester and especially the WRX STI, the MLS gasket is compatible with a broad range of models, underlining its versatility and appeal.

As always, when considering such a significant modification, it’s crucial to consult with a trusted mechanic or specialist to ensure an accurate installation and to maximize the benefits. The decision to switch to an MLS gasket should be seen as a valuable investment in your vehicle’s future, ensuring that it continues to deliver the performance that Subaru is known for.