Car ownership 101: Exhaust leaks

A potentially dangerous problem
by Paulo Rafael Subido | Sep 3, 2018

I started noticing a faint fluttering noise coming from my Miata’s engine bay whenever the engine was under load, but only at very low revs. At engine speeds above 4,000rpm the annoying sound disappeared. It was a very soft clicking noise, and it was driving me mad! What was it? Noisy injectors?  Valve clearance? As it turns out, I had very small holes on the welds of my stainless steel exhaust headers. Here’s how I isolated and solved the problem.


Difficulty level

Hard. Unless you are an experienced welder, best to leave this job to the professionals.

The gear

vehicle lifter; rubber hose; arc welder; protective clothing

Extra tips 

It might take a while to isolate the noise and the source of the leak. Be patient. 

Know your car intimately? Then trust your instincts. The first mechanic I brought my car to thought the sound was coming from the area toward the rear of the exhaust system. He was wrong. I was right.

Exhaust fumes are deadly. Work in a properly ventilated area, please.

Examine the engine and transmission mounts. If these are worn, the exhaust system can be affected.

Guesswork isn’t necessary. Here’s the sure-fire way to pinpoint and isolate leaks in your car’s exhaust system:

Raise the car

Put your car on a lifter. Examine all of the welds that join your exhaust system together. Pay attention to areas that have some rust. Not all exhaust systems are built the same way. Age, weathering, and damage from scraping obstacles or humps can take their toll on components. If your car rides low, it might have more damage.

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Examine the welds

Open up the hood to check the exhaust headers. Telltale signs of a leak are areas with discoloration. If a visual inspection doesn’t reveal any carbon deposits, then it is time to bust out the rubber hose. 

Use a hose 

Start the car. Now, hold one end of the hose against your ear. Use the other end to prod the welds in the exhaust system. A leak, no matter how small, will be enough to send a sound into the hose. The leaks we found were no bigger than pinholes. They are the cause of the minute noise.

Seal the welds

Repair the welds. While you are at it, replace whatever components are worn-out or damaged. Part of the flexible pipe was already wearing through, so I decided to change it with a new one. With the holes patched up, the car runs smooth again. Let’s drive! 




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PHOTO: Paulo Rafael Subido
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