Table of Contents

Summary

The following are the key takeaways from this article:

  • The intake manifold is an integral part of modern automotive engines that directs and distributes the air in the engine’s cylinders.
  • The intake manifold also cools down the heated cylinders during the combustion process.
  • An intake manifold’s important parts comprise a plenum, runners, and gasket.
  • An intake manifold’s common problems include coolant leaks, carbon buildups, and vacuum leaks.
  • You will face increased engine temperature, stalling engine, decreased fuel economy, and check engine light in case of a malfunctioning intake manifold.

Introduction

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Intake manifold is a part of the engine that supplies the desired air during combustion. The position of an intake manifold is mainly between the throttle body and the engine cylinder.

The same manifold can be placed between the carburetor and engine cylinder in older vehicles. The intake manifold not only directs the air into the engine but also ensures that all engine cylinders receive air equally for effective combustion (1). So, the design of an intake manifold can change depending on the engine specifications and the number of cylinders within the engine (5). This article will further shed light on the history, function, parts, and common intake manifold problems.

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History of Intake Manifold

The first manifold injection system was designed back in 1898 by Johannes Spiel. The intake manifold was introduced in two-stroke, four-stroke, aircraft, and Motorcraft engines. In the late 1920s, the efforts to design an intake manifold diesel engine aggravated but were unsuccessful until 1930 when Moto Guzzi first designed an Otto engine with an intake manifold. This system was used in motorbikes from the 1930s to the 1950s (1). Until the 1950s, manifold injection was not common in passenger cars. Still, different automakers did work to test the intake manifold in the passenger cars’ engines. The carburetor was a cost-effective substitute for the intake manifold, and fuel efficiency was not a major concern of the automakers. In the 1950s, Daimler-Benz started integrating the intake manifold in the petrol engines of the Mercedes sports cars (5). The same system was used for passenger cars after analyzing its efficiency. Mercedes became the pioneering automaker to integrate an intake manifold system in their car’s engines. Later, automakers then followed the same custom.

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The function of the Intake Manifold

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An intake manifold is designed to help an IC engine breathe. It features several tubes that ensure the air is coming in and evenly distributed to all the engine cylinders.
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This air is used in the compression to constitute an even air-fuel mixture. Furthermore, this air is also used to cool down the cylinder to prevent engine overheating (3). Engine coolant also runs through the manifold tube, absorbing heat and reducing the engine temperature. The intake manifold is connected to the throttle body, which controls the amount and speed of air entering the manifold. So, in the first step, the air from outside travels inside the manifold through the air filter and intake manifold.

This air further runs through the set of passages known as runners due to the vacuum created by the piston strokes. This vacuum stroke is created due to the downward stroke of the pistons. Finally, the runners are bolted with the engine cylinders, where the air exits the manifold and is swept into the cylinder, mixed with the fuel injected from the fuel injectors (3). It is to be noted that the amount of air entering through the manifold and fuel injectors is dependent upon the engine speed and is controlled by the ECM.

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Important Parts of Intake Manifold

As discussed above, the intake manifold plays an important role in the engine, so it is designed with high-temperature endurance material and can sustain wear and tear. Conventional automakers preferred cast iron to design an intake manifold, but with the focus shifting towards weight reduction, aluminum and composite materials are used to manufacture modern intake manifolds (2). The following are some important parts of an intake manifold:

Plenum

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The intake plenum is the first part of the engine’s intake manifold. Therefore, for transferring air into the cylinder, the pressure within the intake manifold should be greater than the cylinder during its intake stroke.
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The plenum is designed to produce high pressure within the intake manifold. Therefore, it can also be called a pressurized air enclosure that increases the pressure within the intake manifold (4). Several individual tubes run inside the plenum that passes the pressurized air from the plenum to the runners, the second part of the intake manifold.

Runners

Runners are responsible for directing the pressurized air into the respective engine cylinders.
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As the intake manifold is responsible for delivering equal air into each cylinder, the length and width of each runner are equal. The runner’s length is designed according to the distance between various mating and cylinder head to the point where the narrow lines draw from the plenum. The tubes extending out of the plenum enter the runners, so runners generally occupy a small area of the plenum surface (1). This part follows the resonance principle of creating air resonance inside the cavity.

Gasket

A gasket is a mechanical seal between the cylinder head and intake manifold. As discussed in the various function, it also cools down the engine cylinder during the combustion process.
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So, the gasket is responsible for delivering air/engine coolant to the cylinder head. Thus, the coolant or air absorbs the heat from the cylinder helping it to maintain an optimum temperature.

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Common Problems of Intake Manifold

Following are a few common problems of intake manifold:

Coolant Leaks

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As discussed above, the gasket and plenum can have coolant passages inside the engine that can leak or damage over time. This problem is more common in bigger engines such as V6 or V8.

There are multiple coolant passages inside the intake manifold, where the engine coolant flows to cool the cylinder during combustion. The coolant leak can be in the plenum, where you must replace the intake manifold. If there is damage in the runners, they can be welded or repaired depending upon the leak’s extent (2). When the engine is disassembled, always check the intake manifold visually. If the mating surface is in good shape, then replacing the intake gasket can even resolve the problem of a coolant leak in your vehicle. However, if the manifold is damaged, it must be replaced promptly to avoid melting other engine components.

Carbon Buildup

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If you are experiencing a lack of power, a misfiring engine, or a dip in the fuel economy, then there can be a possibility that the carbon has built up inside the intake manifold. This is more common in diesel engines, where fuel lead or carbon can travel inside the manifold, causing blockages and impacting its performance.

Similarly, some turbocharged engines might also face the carbon buildup issue. If the intake manifold is clogged, removing it and cleaning it up manually is feasible (4). However, if the issue persists, replacing the intake manifold with a new one is recommended because carbon has hit the hidden areas of the manifold that cannot be cleaned manually.

Vacuum Leaks

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If you are experiencing a rough startup or a decrease in fuel economy, it can also indicate vacuum leaks in the intake manifold.

Usually, the vacuum leaks are in the manifold gasket causing rough idle start and check engine light illuminating the car’s dashboard. The OBDII fault code, in this case, can be in the P0170 family, indicating the particular error in the intake manifold. Sometimes, the vacuum leak can be due to a worn-out gasket that needs to be replaced. Sometimes, there can be vacuum leaks in the hose or line connecting to the intake manifold. Replacement of the damaged hose or line can resolve the vacuum leak issues. In rare cases, the intake manifold can get damaged. It must be replaced before the vacuum leakage cause other issues in the engine. A hissing sound from the car’s hood can indicate that the intake manifold is facing vacuum leak issues.

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Symptoms of a Bad Intake Manifold

Following are a few common symptoms of a bad intake manifold:

Increase in Engine Temperature

A bad intake manifold can leak an engine coolant. As discussed above, the coolant runs through the small streams in the plenum and the gasket between the cylinder head and the manifold.
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In case of coolant leakage, the coolant cannot run around the cylinder during combustion. As a result, the cylinder will not be cooled down during combustion, raising the engine temperature (2). Of course, you can always check the engine temperature gauge and the coolant reservoir. And suppose there is an abnormal decrease in the coolant level over time, and the engine temperature rises more frequently. In that case, it can indicate a problem in the intake manifold.

Stalling and Rough Idle

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Another symptom of a bad manifold can be stalling the engine and rough idle condition, indicating that the combustion process is not smooth.

There can be leaks in the manifold that would allow more air to enter the manifold that will eventually enter the cylinders, impacting the air-fuel mixture. The common air-fuel ratio is around 14.7:1, but if more air enters the cylinder, the engine can stall at even lower speeds (3). The rough/idle engine start indicates that the intake manifold is malfunctioning and needs replacement.

Decrease in Fuel Economy

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A decrease in fuel economy can also indicate that the intake manifold is malfunctioning. A bad intake manifold will impact the car’s computer calculations, allowing more fuel to enter the cylinders through fuel injectors.

This is an indication that the engine is burning more fuel. Similarly, suppose you observe much black smoke from the exhaust pipe. In that case, it also indicates that the engine is burning too much fuel (2). You can take the car to the service center to get different engine components checked along with the intake manifold.

Check Engine Light

The final symptom of a bad intake manifold can be the illumination of the check engine light on the vehicle’s dashboard. You can always connect a hand-code reader with the OBDII module of your vehicle to further analyze the cause of the check engine light (3). Similarly, engine temperature light can also illuminate. In either case, you have to check the OBDII module that will indicate the particular malfunction in the intake manifold causing these problems.

Common Cost to Resolve the Intake Manifold Issues

The following table illustrates the typical cost required to resolve the intake manifold issues:

Common IssuesCost Required to Resolve the Issue
Dirty/Obstructed Mass Air Flow Sensor$100-200 to replace the faulty MAF sensor
Vacuum Leak$20-50 to replace the damaged intake pipes and hoses
Damaged Gasket$50-100 to replace the damaged gasket seal
Clogged Catalytic Converter$900-2500 to replace the clogged catalytic converter
Damaged Intake Manifold$300-1000 to replace the damaged intake manifold

Conclusion

To conclude, the intake manifold is an important engine part and directs the air to the cylinders and maintains an equal proportion of air in the cylinders. It comprises a plenum, runners, and gasket that help the manifold perform its function effectively. However, certain issues in the manifold or its subcomponents can result in coolant leaks, carbon buildup, or a vacuum leak. Therefore, you should always keep an eye on the symptoms of a bad intake manifold and get it replaced at the earliest to avoid any further engine damage.

FAQs

Now every modern car model has an engine with an intake manifold. Whether your car is a carburetor car or an EFI car, the manifold is there in the engine to effectively distribute. Further, the manifold also cools down the cylinders. You can check your vehicle’s instruction manual to check further if your car has an intake manifold integrated into the engine and its location.

Again it depends upon the vehicle’s make, variant and model, and engine type. Diesel and turbocharged engines will likely face manifold issues after driving for around 100,000 miles. The issue can again arise in normal petrol engines if the engine is not maintained and serviced regularly. So, suppose you face an increase in the engine temperature, hissing engine sound, or rough start along with check engine light. In that case, it is an indication of a bad intake manifold.

With the internet and online auto traders, finding the intake manifold according to your requirements will not be an issue. But there are some old vehicle models whose intake manifold will not be available in the market. In this case, you must find a specialist who can repair the manifold and fix it back in the engine.

About Author

Andrew Ray

Andrew is an automotive technician with 10 years of experience mainly in American and Japanese cars, covering everything from routine vehicle maintenance and engine inspections to tire rotation.