All About Exhaust Gaskets

DIY

Engines and Components

Jefferson Bryant

September 29, 2023

Jefferson Bryant

September 29, 2023

Automotive gaskets - opens in new window or tab. do the critical job of creating a seal between two objects. They form a strong barrier to prevent leaks. If a gasket fails in your exhaust system, you might hear a soft, ticking noise. It’s not only annoying, but can cause massive engine failure if not addressed quickly.

Your engine’s exhaust system is designed to do one thing: move the burned combustion gasses out of the engine, through the catalytic converter - opens in new window or tab., and out into the atmosphere. This requires a sealed system.

Leaks in the exhaust system are not good for you or your vehicle, as the gasses can find their way into the cabin, making the vehicle smell and possibly harming passengers with noxious fumes.

Shop now for exhaust gaskets - opens in new window or tab.

Manifold and Header Gaskets

Most OEM engines use exhaust manifolds - opens in new window or tab. that are typically large cast iron pieces. Manifolds open to each cylinder. Thus, all the cylinders dump the exhaust into a small individual port that connects to a large open chamber. Some engines use longer ports and a smaller open chamber.

Headers - opens in new window or tab. are individual pipes for each cylinder that merge into a collector. They’re mostly aftermarket upgrades, though a few high-performance OEM applications use headers instead of manifolds.

Exhaust gaskets comparison — From left: fiber composite, graphite, MLS, and copper. (Photo: Jefferson Bryant)

The manifold or header bolts directly to the cylinder head - opens in new window or tab. with a gasket between them. These gaskets are commonly made from one of four materials:

Fiber or Composite

These are the most common exhaust gaskets used in OEM applications. They use two layers of fiber material. The first, essentially a heat-resistant thick paper, allows the gasket to conform to the irregular surfaces of the head and manifold. A metal center layer, usually steel, gives strength and resistance to heat blow-out.

Graphite

Graphite has much higher heat resistance than fiber. These gaskets are thicker than fiber composite gaskets. This allows them to fully form between the cylinder head and the manifold or header. Like fiber composite gaskets, graphite gaskets may also have a steel core. Graphite gaskets are excellent for leak-prone headers.

Multi-Layered Steel

Many OEMs are switching to multi-layered steel (MLS) gaskets for all engine gaskets, including the exhaust side. Unlike other materials, these are reusable and highly unlikely to blow out. They usually have three layers and are suitable for stock and high-performance applications.

Copper

In race or ultra-high-performance engines, the exhaust pressures are much higher. Copper gaskets have been the go-to solution to header leaks since the 1960s, as they easily conform to surfaces and resist the extreme heat from high-performance engines. They are not cheap and are only made for the most popular engines.

Exhaust Flange Gaskets

Exhaust flanges are on the other side of the manifold/header and any other joint used in the system, such as bolt-on mufflers, catalytic converters, or other pipe sections. The key word here is bolt-on, as you don’t use gaskets for slip-fit or V-band flanges. These gaskets are commonly made of fiber, fiber composite, MLS, or donuts.

Gen V GM Corvette LT1 exhaust flange close-up view — The output flange gasket can range from the basic three-bolt triangle to oddball flanges like this Gen V GM Corvette LT1 flange. (Photo: Jefferson Bryant)

Fiber/Paper

Plain paper and fiber gaskets have been used for header collectors for decades, but they are largely terrible. They tend to burn up very quickly and have a bad habit of leaking, even when new.

Donut

A donut gasket is a thick ring gasket in a special groove or flared pipe to seal the two parts together. These are very thin, often made of compressed graphite with a metal core, and only for specific applications.

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Signs of a Leaking Exhaust Gasket

Besides the ticking noise, you might notice these symptoms: exhaust smell in the cabin, decreased performance, reduced fuel efficiency, a check engine light - opens in new window or tab. putting your engine into limp mode, and even burned valves, depending on where the leak is.

Stock GM LS-series Vortec exhaust manifold — This stock GM LS-series Vortec exhaust manifold is a better design than most stock manifolds. (Photo: Jefferson Bryant)

A leak at the manifold tends to be loudest under the hood, and you will likely see some soot burn around the leak on the cylinder head. While this is not an immediate problem, the cold air pulled into the cylinder head from the leak can cause the valve to burn if not addressed quickly. This drastically reduces the engine’s performance and requires major service.

Leaks at the collector flange or further down the exhaust make ticking noises but are loudest under the car. These leaks let out gasses that can stink up your interior and make the vehicle unsafe. At the collector, a leak can pull cold air into the system and, if close enough to an oxygen sensor - opens in new window or tab., cause the engine to run poorly. It can also burn up the O2 sensor itself.

How to Repair Exhaust Gaskets

Here are a few basic steps to follow:

Warm up the engine to operating temperature, shut off the engine, and then carefully spray penetrating oil on all bolts you need to remove.
When the engine has cooled off, remove the manifold and header bolts.
Pull the manifold away from the engine and remove the old gasket.
Scrape both surfaces with a metal gasket scraper.
Replace the gasket.
Bolt the manifold back on.

Hooker LS cast iron exhaust manifold — Hooker’s LS cast iron manifolds are a copy of the Vortec LS manifolds with a few upgrades. (Photo: Jefferson Bryant)

Most vehicles have enough flex in the exhaust to do this job without removing the entire exhaust. Collector gaskets use the same process, though sometimes you need a rubber mallet to knock the pipes apart. The most challenging part of these repairs is getting to the bolts.

Gasket Replacement Costs

For most applications, manifold exhaust gaskets cost anywhere from $10 to $50. If you don’t do the work yourself, labor can range from $100 to $400, depending on how hard it is to get to gaskets.

Headers use multiple tubes instead of a large log-style manifold. (Photo: Jefferson Bryant)

Collector gaskets range from $5 to $50, depending on the style, and the labor is typically $100 to $300. Be prepared to spend more on replacement nuts and bolts, as exhaust bolts have a bad habit of breaking because of the heat cycles.

Your vehicle’s exhaust system was designed as a sealed system. If the gaskets start to leak, you will develop drivability issues and have that annoying tick all the time. If left unchecked, a manifold gasket leak can ruin your engine’s exhaust valves, so it is best to address a leak as soon as possible.

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About the author

Jefferson Bryant

Jefferson Bryant, a lifelong gearhead, got his first car when he was two: a Fisher-Price convertible. An industry veteran for over 30 years, he started in car audio, working his way up to product designer for Rockford Fosgate. Bryant has written nine books, countless magazine articles, and produces tech videos on YouTube. A hardcore Buick man, his pride and joy is a 1971 Buick GS Convertible which he swapped with a Procharged Gen V LT1. He even brought his kids home from the hospital in it.

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This article is meant to provide general guidance only. Automotive maintenance, repair, upgrade, and installation may depend on vehicle-specifics such as make and model. Always consult your owner's manual, repair guide for specific information for your particular vehicle and consider a licensed auto-care professional's help as well, particularly for advance repairs.