Used as a source of sealing any gap between the cylinder head exhaust port and the exhaust manifold, the exhaust manifold gasket is one of the most important gaskets on a vehicle. Not only does this component keep toxic exhaust fumes from escaping the engine before they are circulated through an emissions system, it also helps reduce engine noise, improve fuel efficiency and can impact the power your engine develops.
Before the exhaust comes out of the tail pipe, it flows through a series of exhaust pipes and connections in an effort to reduce engine noise and remove harmful exhaust gas and improve engine efficiency. This process begins as soon as the exhaust valve opens and recently burnt fuel is expelled through the exhaust port of the cylinder head. The exhaust manifold, which is connected to the cylinder head with an exhaust manifold gasket in between, then distributes the gases through the entire exhaust system.
These gaskets are commonly manufactured out of embossed steel (in multiple layers depending on the thickness required by the engine manufacturer), high-temperature graphite or in some cases, ceramic composites. The exhaust manifold gasket is subject to absorbing extreme heat and toxic exhaust gases. In most cases, damage to the exhaust manifold gasket is caused by excessive heat coming from one of the exhaust ports. When carbon builds up on the walls of the cylinder head, it can sometimes ignite, causing the exhaust manifold gasket to "torch" or burn in one particular area. If this occurs, the seal between the exhaust manifold and the cylinder head may leak.
When the exhaust manifold gasket has been "pushed out" or "torched," it needs to be replaced by an experienced mechanic. On older vehicles, this process is rather simple; due to the fact that the exhaust manifold is often exposed and easy to access. Newer vehicles with advanced sensors and extra emissions devices can often hinder the mechanic’s ability to remove the exhaust manifold gaskets. However, like any other mechanical component, a bad or failing exhaust manifold gasket may exhibit a few warning signs such as:
Lack of performance from the engine: a leaking exhaust manifold gasket will reduce the compression ratio during the exhaust stroke of the engine’s cycle. This often reduces the performance of the engine and may cause the engine to bog when under acceleration.
Loss of fuel efficiency: a leaking exhaust manifold gasket may also contribute to fuel efficiency loss.
Increased exhaust smell under the hood: if the exhaust manifold gasket seal is broken or pushed out, it will leak gases that can be toxic in many cases. This exhaust will smell different than the exhaust that comes out of the tail pipe.
Enhanced engine noise: a leak from the exhaust manifold gasket will often release un-muffled exhaust, which will be louder than normal. You may also hear a slight "hissing" noise when the gasket is damaged.
Part 1 of 4: Understand the signs of a broken exhaust manifold gasket
It's very difficult for even the most experienced mechanics to properly diagnose an exhaust manifold gasket issue. In many cases, the symptoms of a damaged exhaust manifold and the gasket underneath it are very similar. In both situations, damage will cause an exhaust leak that is often detected by the sensors that connect to the vehicle's ECM. This event will instantly trigger the Check Engine Light and create an OBD-II error code that is stored in the ECM and can be downloaded by using a digital scanner.
The generic OBD-II code (P0405) means that there is an exhaust gas recirculation error with the sensor that monitors this system. This error code often tells a mechanic that there is a problem with the EGR system; in many cases it's due to a cracked exhaust manifold of failing exhaust manifold gasket. The exhaust manifold gasket will be replaced if you're going to need to replace the exhaust manifold gasket regardless. If the issue is with the gasket, you'll have to remove the exhaust manifold in order to inspect and replace.
Part 2 of 4: Preparing to replace the exhaust manifold gasket
Exhaust manifolds can reach temperatures approaching 900 degrees Fahrenheit, which can lead to damage of the exhaust manifold gasket. Under most circumstances, this engine part may last the entire lifespan of your vehicle. However, due to its location and intense heat it absorbs, damage may occur that will require it to be replaced.
Note: To replace an exhaust manifold gasket, you will need to remove the exhaust manifold first. Depending on the make, model and year of the vehicle, other large mechanical systems may also need to be removed in order to gain access to this part. It's a job that should only be completed using the proper tools, materials and resources to complete the job correctly.
Note: The steps documented below are general instructions for replacing an exhaust manifold gasket. Specific steps and procedures will be found in the vehicle's service manual and should be reviewed prior to completing this job.
However, in many cases, if the exhaust manifold gasket has burned, it may cause damage to the exhaust cylinder head ports. If this happens, you'll have to remove the cylinder heads and repair the burnt port damage; as simply replacing the gasket will not solve the problems you're having. In fact, in many situations it can lead to serious damage of exhaust cylinder hardware like valves, retainers and keepers.
If you decide to complete this job, you'll most likely have to remove multiple components in order to gain access to the exhaust manifold. The specific parts that need to be removed will depend on your vehicle, however, most of the time, these parts will need to be removed to have full access to the exhaust manifold:
- Engine covers
- Coolant lines
- Air intake hoses
- Air or fuel filter
- Exhaust pipes
- Alternators, water pumps or air conditioning systems
Purchasing and reviewing a service manual will give you detailed instructions on completing most minor or major repairs. We recommend that you review the service manual before attempting to complete this job. However, if you review all the required steps and you don't feel 100% confident about replacing the exhaust manifold gasket on your vehicle, contact a local ASE certified mechanic from YourMechanic.
Boxed end wrench(s) or ratchet wrench set(s)
Can of Carb Cleaner
Clean shop rags
Coolant container (extra coolant to refill radiator)
Flashlight or drop light
Impact wrench and impact sockets
Light grit sandpaper, steel wool and gasket scraper (in some cases)
Penetrating Oil (WD-40 or PB Blaster)
Replacement exhaust manifold gasket & exhaust pipe gasket
Safety equipment (safety glasses and gloves)
Tip: Some exhaust manifolds on smaller cars and SUV's are directly attached to the catalytic converter. Whether it does or not, the exhaust manifold will require two new gaskets.
The first is the exhaust manifold gasket that attaches to the cylinder head. The other is a gasket that separates the exhaust manifold from the exhaust pipes. Please refer to your vehicle's specific service manual for the exact materials and steps for replacing the exhaust manifold. Also, make sure to complete this job when the engine is cold.
Part 3 of 4: Replace the exhaust manifold gasket
- Note: The following procedure details the general instructions for replacing an exhaust manifold gasket. Always refer to your vehicle's service manual for the exact steps and procedures for replacing the exhaust manifold gasket on your exact vehicle make, model, and year.
Step 1: Disconnect the vehicle's battery. Remove the positive and negative cables to disconnect power to all electronic components before removing any parts.
Step 2: Remove the engine cover. Remove the bolts that secure the engine cover by using a ratchet, socket and extension and remove the engine cover. Sometimes there are snap connectors or electrical harnesses as well that need to be removed in order to take the cover off the engine.
Step 3: Remove the engine components in the way of the exhaust manifold. Each vehicle will have different parts that are in the way of the exhaust manifold gasket. Refer to your vehicle service manual for exact steps on how to remove these components.
Step 4: Remove heat shield. To remove the heat shield in most cases, you'll need to unscrew two to four bolts that are on top or to the side of the exhaust manifold. Refer to your vehicle service manual for exact instructions.
Step 5: Spray the exhaust manifold bolts or nuts with penetrating fluid. To avoid stripping nuts or breaking the studs, apply a liberal amount of penetrating oil on each nut or bolt that holds the exhaust manifold on the cylinder heads. Wait five minutes before you attempt to remove these nuts so the fluid can soak into the stud.
After completing this step, crawl underneath the vehicle or if the vehicle is raised on a rack, spray the bolts connecting the exhaust manifold to the exhaust pipes. Most of the time, there will be three bolts connecting the exhaust manifold to the exhaust pipes. Spray penetrating fluid on both sides of the bolts and nuts and let it soak in while you remove the top portion.
Step 6: Remove the exhaust manifold from cylinder head. Remove the bolts that secure the exhaust manifold to the cylinder head. Using a socket, extension and a ratchet, remove the bolts in any order however when you install the new manifold after replacing the exhaust manifold gasket, you'll need to tighten in a specific order.
Step 7: Remove exhaust manifold from exhaust pipe. Use a boxed end wrench to hold onto the bolt and a socket to remove the nut (or vice versa depending on your ability to access this part) and remove the bolts that secure the two exhaust systems. Remove the exhaust manifold from the vehicle after completing this step.
Step 8: Remove old exhaust manifold gasket. Once the exhaust manifold has been removed from the vehicle, the exhaust manifold gasket should easily slide off. However, in some cases, the gasket will be fused to the cylinder head due to excessive heat. If this is the case, you'll need to use a small scraper to pry the gasket off the cylinder head.
- Warning: If you notice that the cylinder head had fused the gasket to the exhaust ports, you should remove the cylinder heads and have them inspected and rebuilt if needed. In many cases, damage of this sort is caused by a malfunctioning exhaust valve. If not repaired, you'll have to complete this step again sooner rather than later.
Step 9: Clean the exhaust ports on the cylinder head. Using a can of carb cleaner, spray onto a clean shop rag and then wipe the insides of the exhaust ports until the port appears to be clean. You should also use some steel wool or very light weight sandpaper grit and lightly scrub the outsides of the ports to remove any pits or residue on the outside of the exhaust port. Again, if the cylinder head looks discolored or is damaged, remove the cylinder heads and have them inspected or repaired by a professional machine shop.
After installing the new gasket, you'll have to install the bolts holding the exhaust manifold onto the cylinder heads in a certain pattern. Please refer to the service manual of your vehicle for exact instructions and recommended torque pressure settings for reinstalling a new exhaust manifold.
Step 10: Install the new exhaust manifold gasket. The steps for installing the new exhaust manifold gasket are in reverse of the removal steps as indicated below:
Attach the new exhaust manifold gasket onto the studs on the cylinder head
Apply anti-seize to the studs on the cylinder heads that attach the exhaust manifold to the cylinder head
Install a new gasket between the bottom of the exhaust manifold and the exhaust pipes
Attach the exhaust manifold to the exhaust pipes below the vehicle after applying anti-seize to each bolt
Slide the exhaust manifold onto the cylinder head studs.
Hand-tighten each nut onto the cylinder head studs in the precise order as instructed by the vehicle manufacturer until each nut is hand-tight and the exhaust manifold is flush against the cylinder head equally
Tighten exhaust manifold nuts to the require torque pressure and in the exact pattern as recommended by the vehicle manufacturer
Reinstall heat shield onto exhaust manifold
Reattach engine covers, coolant lines, air filters and other parts that were removed to gain access to the exhaust manifold
Refill radiator with recommended coolant (if you had to remove coolant lines)
Remove any tools, parts or materials you used in this job
Reattach battery terminals
Note: If your vehicle had an error code or a light on the dashboard, you need to follow your manufacturers recommended steps for clearing old error codes before you test the exhaust manifold gasket replacement.
Part 4 of 4: Test the repair
When you test fire the vehicle any symptoms that were apparent before you replaced the exhaust manifold gasket should be gone. After you've cleared the error codes from the computer, test-start your vehicle with the engine hood up so you can complete the following checks:
- LISTEN: for any sounds that were symptoms of the broken exhaust manifold gasket
- LOOK: for any leaks or gases escaping from either the exhaust manifolds connection to the cylinder head or the exhaust pipes below
- OBSERVE: any warning lights or error codes that appear on the digital scanner after you start the engine
- CHECK: fluids that you may have needed to drain or remove including coolant. Make sure to follow manufacturer's recommendations on refilling coolant
As an added test, it is a good idea to road test the vehicle with the radio off to listen for any road noise or excessive noise coming from the engine compartment.
As indicated above, if you've read these instructions and still don't feel 100% confident in completing this repair, or if during the pre-installation inspection you determine that removing additional engine components is beyond your comfort level, please contact one of our local ASE certified mechanics from YourMechanic.com to replace your exhaust manifold gasket.
This article originally appeared on YourMechanic.com as How To Replace An Exhaust Manifold Gasket and was authored by Tim Charlet.