An exhaust manifold leak can be a very loud indicator that something is wrong with your vehicle. If let untreated, an exhaust leak can seriously damage your engine or even pose a health hazard by letting toxic fumes into the cabin. Many times the issue can be traced back to the exhaust manifold gasket. The purpose of the manifold gasket is to seal between the engine cylinders and the exhaust system.
The gasket is made out of multiple layers of embossed steel and sometimes they are also made out of graphite and ceramic composites. Its also not uncommon for these gaskets to be made out of a combination of materials in different layers.
Usually an exhaust manifold leak will produce several symptoms that can alert you have a problem. While it may seem like your vehicle can run fine with these symptoms, a manifold leak should not be ignored.
1. Loud Engine Noise
The first and most common sign of any exhaust issue is loud engine noise. Any lack of sealing or crack in the manifold will cause a dramatic increase in noise. In many cases a cracked manifold will create a hissing or tapping sound coming from the engine bay. This sound could be loudest or most pronounced at a cold start. This is because as the gasket heats up, it expands and could seal the leak better.
The gaskets and exhaust go through thousands of heating and cooling cycles with every start of the engine. As the gaskets heat up they expand and contract as they cool. These heating and cooling cycles stress the gasket and can cause cracks leading to exhaust manifold leaks.
In many cases the sound of a leak is similar to a ticking or puffing sound. This sound will normally be most noticeable when the engine is cold, and louder the closer you get to the engine.
2. Poor Fuel Economy
Reduced gas mileage is another symptom of an exhaust manifold leak. The leak will cause a lower pressure in your exhaust system. It can trick the o2 sensor into thinking your engine has a lean mixture. The ECU will then increase its fuel delivery causing a rich mixture and poor fuel economy.
Poor gas mileage can be caused by a number of things. However if you notice you have a louder engine along with a worse gas mileage, you probably have an exhaust leak.
3. Loss of Acceleration
Exhaust manifold leaks can do odd things to the fuel delivery of your vehicle. Its not uncommon to notice a loss of performance when your manifold is leaky. Again you may just have one of these symptoms or all of them. So if you do notice other symptoms along with a power loss, its just further confirmation of an exhaust leak.
4. Burning Smell from the Engine Bay
Exhaust gases are hot, and they’re meant to be routed through the entire exhaust system. When these gases escape right after leaving the combustion chamber, they are incredibly hot. These can cause serious damage and premature wear to other parts of your engine. Its not uncommon for an exhaust manifold leak to cook other components under your hood. As this happens you may notice strange smells coming from your engine bay. This is never a good sign, and you should investigate to see where the burning smell is coming from before it leads to a fire.
5. Exhaust Fumes in the Cabin
This one is pretty obvious symptom, but it is the most dangerous so it should be mentioned. If you small exhaust fumes inside the car you definitely have an exhaust leak. This problem poses a serious health risk and should be dealt with immediately.
Bonus: Check Engine Light Is On
A failed exhaust manifold can cause the check engine light to come on. Typically the engine will figure out something is wrong based on the O2 sensor’s readings. The exhaust manifold leak or crack will change the level of O2 in the exhaust. The engine’s ECU will recognize that something isn’t right and it’ll trip the check engine light. However, not every exhaust manifold leak will cause a check engine light to go on.
Exhaust Manifold Failure Modes
Generally there are three common exhaust manifold leak failure modes.
- Cracked manifold
- Failed manifold gasket
- Broken or loose exhaust manifold screws
These are the three most common failure modes. A cracked manifold can be the most costly. The best repair is to replace the part completely. I’ve tried to previously repair exhaust cracks with filler material, and the repair never seems to last. The filler expands and contracts at a different rate than the manifold and it causes wear and tear until the filler material is slowly eroded. Using a filler material is never a permanent fix, but if the crack is small enough that it could be filled with a weld, that would be a permanent fix. JB weld doesn’t count!
A failed manifold gasket is still a labor intensive repair, but parts wise a cheaper repair. Over time these gaskets can crack due to constant heating and cooling cycles with the engine. The cracks will then expand with each hot/cold cycle.
Lastly the source of the leak could be as simple or as difficult as broken or loose screws. Exhaust manifold bolts are subject to lots of vibration from the engine. This vibration can loosen bolts or break them completely. A loose bolt can allow for a leak path which could be the source of your problems.
How to Find the Leak
The first thing to do is start with a visual inspection of your engine bay. Make sure the engine is cold or that you’ve allowed several hours for it to cool off since your last drive. Look for black soot around the manifold. This is a common sign of an exhaust leak.
During your inspection, look for any obvious cracks or loose bolts. Its not a bad idea to attach a wrench to the bolts and check to see if they’re torqued.
There is one easy trick to find out if you have a leak. With the car engine off, place a vacuum cleaner in your exhaust pipe. Make sure you adjust your vacuum so its pushing air into your exhaust. Then spray soapy water all over your exhaust and look for bubbles.
Exhaust manifold leaks is a big deal, and you shouldn’t ignore it. The symptoms can manifest themselves in various ways or in any combination of symptoms. There simple steps outlined above you can take to find and isolate the leak. The more you know about your car and its problems the easier and cheaper it will be to repair it.