The exhaust manifold gasket is the sealing mechanism between the exhaust manifold and the engine’s cylinder head. It’s a vital part of the exhaust system and also indirectly contributes to emission control.
V8 engines from the 70s through the 80s that had cast iron manifolds and cast iron cylinder heads didn’t come with exhaust manifold gaskets. Each cast iron manifold was machined during the manufacturing process to fit so precisely against the cast iron cylinder head so that no gasket was necessary.
But once that manifold was removed during service, an exhaust manifold gasket was necessary when the exhaust manifold was being reinstalled due to the shape-changing characteristics of cast iron that has been heated to several hundred degrees and allowed to cool over and over.
Modern engines will have some kind of exhaust manifold gasket today. Because heads are aluminum and exhaust manifolds are steel, the gasket will either be steel, or, in some cases, it may be some kind of composite asbestos or aramid type material heavily coated with slippery graphite to handle the “scrubbing” effect of the aluminum head and the steel manifold expanding and contracting at different rates.
Note that there is also the gasket between the exhaust manifold and the header pipe or catalytic converter, which is more likely to fail than the gasket between the manifold and the cylinder head.
Like any other car part, the exhaust manifold gasket can wear out over time, although take note that this does not usually happen. A leaking exhaust gasket can impact and exhaust emissions. If the gasket leak is bad enough, it can even become a fire hazard, especially if the rocker arm (valve) covers are seeping oil that trickles down across the point of the leak.
Here are some warning signs of a bad exhaust manifold gasket:
Hissing or tapping sounds are some of the most common symptoms of a bad exhaust manifold gasket. You may also smell exhaust fumes if you happen to be running the A/C on anything other than “max” or “recirc.”
If you hear hissing, clicking or tapping sounds when the engine is started cold that then fade away as the engine heats up, these may indicate an exhaust leak from a cracked cast iron exhaust manifold if your engine has one. But on the more common steel exhaust manifolds today, if they are cracked, they don’t typically close during heat expansion as a crack in cast iron does.
Oxygen sensors don’t sense fuel, they sense oxygen. Since the engine’s exhaust has pressure waves pulsing through it, any breach in the exhaust system from a failed gasket, loose fasteners, or a cracked manifold, can draw varying amounts of oxygen into the exhaust stream to be picked up by the O2 sensors and misinterpreted as a lean air/fuel situation.
This will cause the engine controller (PCM/ECM) to add some fuel that isn’t needed, which will have an effect on fuel economy but won’t typically affect engine performance in a noticeable way.
If an exhaust leak is serious enough, it can reduce exhaust gas recirculation flow to the point that codes are stored for that part of the emissions system. But a leak this serious will typically be noisy enough that the exhaust leak itself will most likely become the focus the repair.
If you can smell burning metal or plastic from the direction of the engine, you might have a bad exhaust manifold gasket. There are usually wires and plastic parts near the gasket that may burn or melt when exposed to high temperatures. Again, there’s the risk of a fire hazard with a significant exhaust leak, particularly if the exhaust leak is directed at anything flammable.
The exhaust gasses produced by the combustion process are very hot. If the gasses leak out of the exhaust manifold gasket, they might reach the heat-sensitive parts. These parts might melt or even burn, producing a distinct smell and possibly even some smoke. Needless to say, you will need to replace any melted or burned parts as well as the gasket itself.
An exhaust manifold has one exhaust manifold gasket. In engines that have two manifolds, such as V6 and V8 engines, each manifold gets its own gasket.
Most exhaust manifold gaskets are made of embossed steel. Some gaskets will have multiple layers for added durability and strength. Other materials include ceramic composites, graphite, and high-temperature fiber.
There are other gaskets in the exhaust system that seal other connection points. Examples include flange gaskets and ring gaskets. They usually use the same materials as exhaust manifold gaskets.
The exhaust manifold gasket serves as the seal for the connection between the exhaust system and engine (there’s also another gasket between the manifold and the header pipe or light-off catalyst). The gasket contains exhaust gasses as they flow into the catalytic converter and then the rest of the exhaust system. The gasket also prevents exhaust noise within the engine compartment.
Most manufacturers design their exhaust manifold gaskets to run for numerous heat cycles, which translates to many years. However, the gaskets can degrade faster and fail earlier depending on various factors.
For example, a collision with an obstacle or another vehicle can apply enough shock to fracture the gasket, allowing exhaust gasses to leak out of the ensuing crack. If the seal is made of steel and it loses its corrosion protection to damage or extended exposure, it can corrode and fail.
Some repair and maintenance jobs require removal of the exhaust manifold gasket to access other engine parts for inspection and repair. While mechanics usually take care in uninstalling the gasket, they can inadvertently damage it anyway.
It’s best to avoid driving your car until you have repaired or replaced its faulty exhaust manifold gasket. The reduction in fuel efficiency can make you drop by the gas station more often to fill your fuel tank. And if your vehicle is slated for an emissions test, it’s going to fail. If you keep driving with a leaky gasket, the exhaust valves might fail in the long run and require replacement themselves.
A faulty exhaust manifold gasket can cause a whole host of problems like bad fuel economy and failed emissions tests. That’s why it’s best to replace your faulty exhaust manifold gasket as soon as possible. Luckily, ordering from CarParts.com is one way to get your new parts quickly.
CarParts.com offers speedy shipping, with orders in the continental US arriving in as fast as two business days. Ordering is a breeze as well with our easy-to-navigate website. You can browse our large catalog of quality aftermarket parts from different brands and choose whatever suits your budget. Be sure to use our built-in vehicle selector to ensure that your parts will fit your vehicle. If you have any questions, reach out to our friendly and helpful customer service team. We’re happy to help around the clock.
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