3 Intake Manifold Leak Symptoms (and Replacement Cost)

Last Updated on January 10, 2020

The components of an engine have gaskets that are placed between them before they’re assembled. These gaskets act as a seal between the components so they can do their jobs properly. You’ll find gaskets are usually made out of metal, rubber, paper, or all three combined together.

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Out of all the gaskets in the engine, the intake manifold gasket is crucial for sustaining the functionality of the engine. If this particular gasket were to start leaking, it would spell trouble for your vehicle.

That is why you need to learn about what the symptoms are of an intake manifold leak. Once you recognize this, you can proceed to fix the problem without wasting any more time.

However, you should take the opportunity to learn about how the intake manifold gasket functions before you start diagnosing it as having a potential leak. That way, you won’t confuse the symptoms of the vehicle with another potential problem it may be having.

What is an Intake Manifold Gasket?

The intake manifold gasket(s) sits between the cylinder head and the intake manifold. Its main purpose is to prevent coolant, oil, or air leaks.

Because of constant expansion and contraction from temperature changes, coolant and oil contamination, and the constant flow of intake air, the intake manifold gaskets can slowly break down and eventually get to the point where is deteriorates enough to cause a leak.

If a leak occurs, the gasket should be replaced as soon as possible to avoid potential engine damage or possibly getting stranded.

Top 3 Symptoms of Intake Manifold Gasket Leak

#1 – Engine Coolant Leak

Engine coolant is sealed by an intake manifold gasket in the engine. If damage were to come to the seal, all the pressurized coolant it is holding back may seep through it.

Often times, the coolant will have debris and dirt inside of it which will create even more problems. If the debris is thick enough, it will cause more wear on the surfaces. Not only that, leaky coolant will also cause air from the outside to get into the engine through the seal.

Anytime oxygen is present, it will drastically increase the amount of corrosion that forms. This will cause even more damage to the surface.

See Also: Symptoms of a Bad Coolant Temperature Sensor

#2 – Overheated Engine

high temperature gauge

When coolant continues to leak, it will eventually cause the engine to overheat. But in some circumstances, the engine can still overheat even if the coolant does not appear to be leaking. Sometimes coolant will leak out of the intake manifold gasket and go right into the intake manifold, causing the engine to overheat.

On the outside, you would not see any signs of this leak. The only way you will know is when the engine starts to overheat and the temperature gauge in your dash rises to a high level. Then you can investigate and determine if this is the problem. If so, then get it fixed at an auto shop right away.

#3 – Air Fuel Mixture Ratio Will Be Affected

air fuel ratio

Air and fuel need to be mixed precisely as it goes into the intake manifold. This allows for proper combustion in the engine. But if there were to be a change in the level of air or fuel in this mixture, it would have a negative impact on the performance of the engine.

Therefore, if you were to have a leak from a damaged intake manifold gasket, then more air may get into the intake manifold and cause an imbalanced air/fuel ratio. Once that happens, the symptoms will typically be rough idling and numerous misfires.

If you experience these symptoms, it may not tell you exactly where the problem is in the intake manifold, but you will at least know that you need to have it checked out.

Intake Manifold Gasket Replacement Cost

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intake manifold gasket replacement cost

The intake manifold gasket is maybe the most expensive gaskets in a car due to its durability requirement and unique shape. A new replacement gasket will likely run you somewhere in the range of $50 to $120 which doesn’t sound so bad.

But the expensive portion will be the work required to replace it since it’s not easy to get to. The labor cost to replace an intake manifold gasket will set you back about $250 to $500. This number could even be higher for sports cars and luxury vehicles.

All together, on average you can expect to pay around $300 to $620 for the total cost of an intake manifold gasket replacement.

Troubleshooting an Intake Manifold Leak

If engines have aluminum cylinder heads on them, you can expect to have corrosion near the ports of the coolant. The intake manifold gasket’s seal bead has plastic under it that may be eaten away as well.

If you see this, then it means the seal will not hold and will be susceptible to leakage. As a result, the gasket would not be the cause of the leak in this case.

Testing for an intake manifold leak should not be attempted by novice mechanics and in most cases you should let a professional handle it. That said, here are the general processes.

Coolant Leak Testing

If coolant leaks on the outside of the gasket, then you can see it with your own two eyes. But if there are internal leaks which cause the coolant to flow into the oil or combustion chamber, then you won’t be able to spot them that easily.

What you’ll want to do is give your system a complete inspection. Start by checking the oil for signs of foaming or other types of contamination. You should also pull the codes so you know exactly what you’re dealing with.

If the codes relate to the oxygen or efficiency sensor, then it means that coolant has gotten into the combustion chamber. Since phosphates are found in the coolant, along with other chemicals, this will cause damage to the catalytic converter and the oxygen sensor.

If you have a V8 or V6 engine, you can use the codes to figure out which bank has the leak. Any big leaks that are in the runner may give you a misfire code. If you experience this problem for extended periods of time, take out all the spark plugs in your vehicle.

See if the electrodes have any chalky white deposits on them because this is the markings that coolant will leave on them. By following these techniques, it will help you determine where the leak is coming from and if more tests need to be done, such as leak down checks or compression checks.

Air Leak Testing

A fuel trim problem can occur if the intake manifold has the tiniest leak. If you just use your eyes and ears to find the leak, it will become very time-consuming.

Anytime air leaks through the intake manifold, it will cause air to get sucked in rather than pushed out. Whatever is in the air that’s pulled in will compromise the mixture of the fuel and air, which will impact the emission system and the engine system.

If you have a smoke machine, then multiple leaks can be diagnosed in a shorter amount of time. This machine does this by allowing the intake manifold to become pressurized while placing vapor and smoke into the system. So, if a leak truly does exist, then smoke will be drawn out.

Find a vacuum port and attach the smoke machine to it just like you would have the brake booster connected to the supply line. Ensure that you have the right sized plug when blocking the throttle body. You’ll also want the PCV system to be blocked off as well.

If the PCV system or oil filter has smoke coming out of it and the engine is not misfiring, then it probably means there is a crack or leak underneath the intake manifold. It may also mean the valve seals or guides are too worn out.

 

4 thoughts on “3 Intake Manifold Leak Symptoms (and Replacement Cost)”

  1. Desperately in need of advice:

    Suppose you perform a head gasket job on a 2004 Outback (Subaru) after the car overheats and the radiator cracks. Only 24 hours after the shop completes the work the belts drop and bend valves at highway speed, causing the entire job to be repeated (and then some). The car is driven for five months while it continues to leak a small amount of oil onto the driveway. The same shop replaces the lower crankshaft seal (at cost to customer) to resolve oil leak. Not long after that, a check engine light comes on. Shop owner reads a “P1092” code, which he says makes no sense as that code on a Subaru is reserved for a “tumble generator valve”, which he says corresponds to a WRX but not to an Outback. Customer pulls car from shop and takes it to dealer, where dealer reads the same code and is also baffled. Dealer eventually concedes that the “tumble generator valve” exists after all but upon replacing it, the CEL does not clear. Customer later learns that the actual part that is installed by dealer is not called a “tumble generator valve” but a “Fuel Injection Idle Air Control Valve” (Subaru part 14120AA020). After the CEL does not clear, dealer removes part and then informs customer that they need to pay almost a thousand dollars to clean the intake manifold. Original mechanic continues to insist that the ECU is bad and rejects the notion that the intake manifold requires cleaning.

    Is the customer impression correct: Intake manifold repair should be covered by the shop owner’s 2x head gasket job, less than one year prior, on the basis that the head gasket could not be accessed without tear-down of the aforementioned intake manifold. At that time, should not the intake manifold have been cleaned of carbon and/or debris created when the belts dropped and the valves bent? Moreover, at that time, should not the intake manifold gasket have also been inspected and replaced since the car had over 160,000 miles on it?

    Customer checked records and does not see any indication that in the course of doing the 2x head gasket work that the intake gasket was replaced. Is it possible that the P1092 code corresponds not to a failing “tumble generator valve” or even “carbon deposits” in the manifold but a failing gasket (i.e. a bad seal)?

    The symptom that occurred with the P1092 code was failure of the car to accelerate properly at low speeds (difficulty getting the car up to highway speed). Could this kind of drivability problem be created by A) a “tumble generator valve” in a 4 cylinder Outback, B) a failing intake manifold seal, or C) carbon buildup in the manifold, or D) debris that accumulated in the intake manifold after the valves bent?

    The bottom line from the customer perspective is whether or not this is a NEW problem for which it is necessary to fork over another thousand dollars OR if the shop owner should take responsibility for resolving the problem since these engine components had to be disassembled less than a year ago to make way for the back-to-back head gasket repair jobs.

    Reply
    • That’s a tough one. As a disclaimer, I am not a professional mechanic and have never been in this situation, but I will do my best to help.

      Was the engine pulled as part of the head gasket job? You can do the head gaskets on these cars by jacking up the motor so the heads clear the body instead of removing it, but many people find it easier to just pull the whole thing out of the car.

      If the leaking seal was easily accessible during the head gasket job and the customer was not informed that it should be replaced, this seems like a mistake on the shop’s part. The front crank seal is accessible regardless of whether or not the engine is in the car. If the motor was pulled, I would expect the shop to replace the rear main seal or at least run it by the customer, and have them sign off on it if they opted not to have the shop replace the seal.

      I feel the same about the intake manifold gaskets, which should have been replaced.

      I am almost certain these Outbacks do not have TGVs. However, if the code was thrown very soon after the crank seal was replaced, I am inclined to believe it was caused by the work that was done (despite being seemingly unrelated). I would be pleased with a shop that performed the diag at no cost to the customer as a goodwill gesture. If the root cause is determined to be unrelated to prior work, the customer should pay for the actual repair.

      Reply
    • Look on the internet for the repair manual pdf for your car and read the complete instructions for changing the head gasket on the engine you have in your car. It will tell you exactly what should have been done, gaskets replaced and cleaning of parts. In my opinion they should have asked you if you wanted the timing chains replaced as a precaution while they had it all apart. Repair manuals can be a handy read anyway as it will give you more knowledge about your car and possibly prevent you being ripped off by unscrupulous mechanics

      Reply
    • Yes. He screwed you. That intake gasket should’ve been replaced when it was out. Period. Full stop. Especially at 160k on the dash! He should’ve known better.

      Your failure to accelerate at low speeds is almost certainly due to extra air being pulled in through your leaky intake manifold. The engine is probably running super lean, and therefore can’t make the power it needs to get you off the line. Fight this. Go get an opinion from a licensed mechanic you trust, ask him if he’d mind signing an affidavit, and sue that pos.

      Keep in mind, however, that I’m flying blind here and can’t be 100% certain that this is the exact cause of your problem. That being said, if all the information you’ve provided here is accurate to the letter, that man screwed you, and the dealership is just grabbing at straws because they don’t want to invest the time in properly diagnosing your car. I’ve seen it a hundred times. They’re often very lazy.

      Reply

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