Intake Manifold: 5 Symptoms Of Bad Intake Manifold Gaskets

What is Intake Manifold?

The intake manifold carries air to the cylinders. Along with the throttle body, air intake, and fuel delivery system, the manifold helps deliver the appropriate air-fuel mixture for combustion in the engine.

Intake manifolds are built with a couple of main components, which include the plenum and the runners. The plenum is a reservoir that holds air until it’s needed in the cylinders. The runners carry that air from the plenum to each cylinder head.

In automotive engineering, an inlet manifold or intake manifold is the part of an engine that supplies the fuel/air mixture to the cylinders. The word manifold comes from the Old English word manigfeald (from the Anglo-Saxon manig [many] and feald [repeatedly]) and refers to the multiplying of one (pipe) into many.

In contrast, an exhaust manifold collects the exhaust gases from multiple cylinders into a smaller number of pipes often down to one pipe.

The primary function of the intake manifold is to evenly distribute the combustion mixture to each intake port in the cylinder head. Even distribution is important to optimize the efficiency and performance of the engine. It may also serve as a mount for the carburetor, throttle body, fuel injectors, and other components of the engine.

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Due to the downward movement of the pistons and the restriction caused by the throttle valve, in a reciprocating spark ignition piston engine, a partial vacuum (lower than atmospheric pressure) exists in the intake manifold.

This manifold vacuum can be substantial, and can be used as a source of automobile ancillary power to drive auxiliary systems: power-assisted brakes, emission control devices, cruise control, ignition advance, windshield wipers, power windows, ventilation system valves, etc.

This vacuum can also be used to draw any piston blow-by gases from the engine’s crankcase. This is known as a positive crankcase ventilation system, in which the gases are burned with the fuel/air mixture.

The intake manifold has historically been manufactured from aluminum or cast iron, but the use of composite plastic materials is gaining popularity.

intake manifold

How Does an Intake Manifold Work?

The intake manifold uses pistons to conduct the air-fuel mixture and the coolant through the engine block via the valves to the relevant areas. It is important that these mixtures are distributed evenly, otherwise, the engine will not work as efficiently.

Why Do Intake Manifolds Fail?

Intake manifolds fail because of the high levels of constantly changing heat and pressure they are subjected to on a daily basis. The strain they are put under inevitably leads to cracks developing – it is up to the driver to diagnose the problem and deal with it at the earliest opportunity.

5 Symptoms Of Bad Or Failing Intake Manifold Gaskets

The intake manifold gaskets are some of the most important gaskets found on an engine. Gaskets are the seals placed between engine components before they are assembled in order to provide a reliable seal. They can be made of paper, rubber, metal, and sometimes a combination of the three.

The intake manifold gaskets are responsible for sealing the intake manifold against the cylinder head(s). Apart from sealing engine vacuum, certain designs will also seal engine coolant. When the intake manifold gaskets have an issue, they can cause drivability problems and even engine overheating. Usually, a faulty intake manifold gasket will produce a few symptoms that can alert the driver of a potential issue.

1. Coolant leaks

Another symptom of a faulty intake manifold gasket is coolant leaks. Some intake manifold gaskets also seal engine coolant, and if the gasket wears out it may lead to a coolant leak. This may produce a distinct coolant smell, along with steam, and drips or puddles of coolant underneath the vehicle. Coolant leaks should be addressed as soon as possible, in order to prevent them from becoming a greater issue.

2. Engine Overheating

Engine overheating is another symptom of a possible issue with the intake manifold gaskets. A coolant leak will eventually lead to engine overheating when the coolant level drops too low, however, there are instances where overheating can occur without any visible leaks.

If the intake manifold gaskets leak coolant into the intake manifolds the engine may overheat as a result, without any visible external leaks. Any coolant leaks should be addressed as soon as possible to prevent the possibility of serious engine damage occurring due to a bad intake manifold gasket.

3. Engine Stalling

When the engine stops turning or is turning too slowly, then stalling will occur. This can happen when a faulty intake manifold gasket causes a vacuum leak, which messes up the ratio of air to fuel.

Then you could be driving and all of a sudden experience a stalled engine. Of course, there could be many other reasons for a stalling engine, but a bad intake manifold gasket is surely one of them. Go see a mechanic to have them verify if it is this gasket or not.

A mechanic will be able to perform a smoke test to rule out vacuum leaks. A smoke test injects smoke into the intake system. If there is a leak in the system, smoke will come out from an area it’s not supposed to.

4. Bad Fuel Economy

Since a faulty intake manifold gasket causes a disruption in the air to fuel ratio, then your engine is going to consume more fuel than normal.

This means you will be spending more money on gas for doing the same amount of driving that you normally do. As a result, your fuel economy will decrease greatly.

5. Loss of Acceleration

Aside from an engine stalling, you may notice a simple loss of acceleration after you step on the gas pedal. You may get a little bit of power at first, but then the acceleration will stop and start again as you keep your foot on the pedal.

You obviously shouldn’t continue to drive your vehicle when it is in this condition since it’s dangerous to do so. If you are experiencing two or more of the other symptoms, then you definitely need to have your intake manifold gasket replaced promptly.

How Much Does It Cost to Fix? Can’t I Do It Myself?

Unless you’re an experienced home mechanic with the proper tools and a safe place to work, it’s probably best to leave manifold work to the pros. The steps to remove, replace, and safely reconnect everything can be difficult to understand without experience, and the consequences of messing something up can be serious.

Having said that, it’s important to note that paying someone to fix an intake manifold won’t be cheap. On average, you can pay between $400 and $600 for intake manifold repairs. Labor is the major expense here, ranging from $340 to 420. The parts, on the other hand, only cost about $80-$165.

Can You Drive with a Bad Intake Manifold Gasket?

While it is indeed often possible to drive with a bad intake manifold gasket, you should not drive too far. Issues like this don’t go away on their own, and they also don’t tend to get better with time.

Leaking additional unmetered air into the combustion chamber has the potential to make the car run lean, which means the engine is likely to run hotter. Knock or pre-detonation is also more likely. Too much knock under load can actually destroy a perfectly good engine.

An overheating engine is likely to cause additional damage to the engine, including a warped or cracked head or a cracked block. This damage would cost far more to repair than a simple intake manifold gasket replacement normally would.