Intake Manifold Leak Symptoms

Intake Manifold Leak Symptoms

Last Updated August 18, 2023 | Alison Smith

Although they may not be the most exciting, intake manifolds have a pretty important job. Intake manifolds distribute air and fuel to the cylinders, enabling the combustion process. But as with anything, the intake manifold can spring a leak.

What Causes a Leaky Intake Manifold?

Intake manifold and gaskets against a white background

Intake manifolds connect to the cylinder head using gaskets or seals to keep everything airtight. Over time, these parts can wear out and become less effective. If the gaskets are not sealing properly, they can cause a leaky intake manifold.

Gaskets can be made of different materials including rubber, paper, or metal. They’re designed to last around 50,000 to 75,000 miles, but can wear out quicker and fail. If the gasket can’t provide a proper seal, it can cause lots of issues.

If all the gaskets or seals look good on the intake manifold, then you may need to check that the manifold isn’t cracked itself. Intake manifolds leaked less often when they were made of cast-iron. Now that manufacturers use lighter and cheaper alternatives, such as cast aluminum and plastic, it’s a more common issue.

Plastic manifolds are more affordable but crack easier. The manifold itself can crack from vibrations, engine backfires, overheating, over-tightened fasteners, or mishandling. Hairline cracks won’t cause engine failure, but they can cause other problems like rough idling and improper fuel mixture.

What are the Signs of a Bad Intake Manifold Gasket?

Because the intake manifold gaskets seal in air and liquids, a few things can happen when it springs a leak. Here are a few tell-tale symptoms of a leaky intake manifold or a bad gasket:

  • Improper air-fuel ratio
  • Overheating
  • Engine misfires
  • Decreased acceleration
  • Poor fuel economy
  • Coolant leaks
  • Milky engine oil
  • Backfires or rough idling

It shouldn’t be surprising that many of these issues correlate with each other. If there’s a leak in the intake manifold, then the air-fuel ratio is affected. A leaky intake manifold sucks outside air in, rather than dispersing air out. This can cause performance issues including poor fuel economy, decreased acceleration, and engine misfires.

Coolant leaks can cause the engine to overheat, although they may not always be visible. Sometimes you’ll be able to see coolant leaks under the vehicle while other times the leak is internal.

If it gets to the point where engine performance is greatly affected, the check engine light may even come on. However, that’s usually not the case for minor leaks.

Blue intake manifold gasket component on table

How Do You Test for Intake Manifold Leaks?

It’s not always easy to tell if the intake manifold is leaking. Other than visually inspecting the manifold or seeing if coolant is leaking under the vehicle, there are a few other ways to test for leaks.

Use a Smoke Machine

Although they can be expensive, smoke machines are a quick and efficient way to check for leaks. They are connected to a vacuum line in the car to pinpoint the location of the leak. The vacuum supply line to the brake booster is a good place to connect.

You’ll have to plug up any openings in the intake manifold, including the throttle body. If there’s a leak, you should be able to see smoke or vapor coming out.

Look for Coolant Leaks

It’s easy to tell if the coolant is leaking if there’s a puddle under the car. But coolant leaks aren’t always easy to detect. That’s why dye is sometimes used to make detecting a coolant leak easier. Fluorescent dye goes into the radiator, changing the color of the coolant. A special flashlight or glasses are used to see the colored dye and find the leaks.

Other Ways to Check for a Leak

Check the oil for indications of contamination. If there’s a leak, there may be foaming or the color may appear milky. You can also get it checked out at a repair shop as well.

Can You Drive with a Leaking Intake Manifold?

Yes, it’s typically safe to drive with a leaking intake manifold. But if you’ve got suspicions, it’s always safer to get it checked out sooner rather than later. Leaking intake manifolds can decrease performance, but overheating can eventually cause engine damage. Running too hot can cause engine knock as well.

How Much Does it Cost to Fix an Intake Manifold?

Depending on the repair, it can cost between $200-500 to fix a leaking intake manifold. However, gaskets themselves are much cheaper, so you can save on labor if you’re mechanically inclined and able to fix it yourself.

If the manifold is completely unfixable, you might need to get it replaced. Or you could always upgrade to an aftermarket intake manifold for better performance.

Sources: Symptoms of Bad or Failing Intake Manifold Gaskets, Autoblog | Plastic Intake Manifolds: Checking for Leaks, Underhood Service | Intake Manifold Gasket Diagnosis, Know Your Parts | How to Find a Vacuum Leak, Popular Mechanics

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