What is exhaust leak? And how to locate it

Your car’s exhaust system is like a giant pipe designed to route smelly, harmful gases safely away from the engine and out behind the car. It also helps quiet things down. When there’s a crack, hole, or bad seal anywhere along this pipe, exhaust gases can leak out before they’re supposed to.

Why do you care? Well, exhaust leaks are not just annoying (they can be loud!), but they can also let dangerous fumes (including invisible, odorless carbon monoxide) into your car’s cabin, hurt engine performance, and even cause frustrating “Check Engine” lights related to your oxygen sensors or catalytic converter.

Spotting an exhaust leak often relies on your senses. Here’s what to look for and listen for:

1. Listen for the Noise: This is often the most obvious sign! Exhaust leaks sound like a ticking, hissing, or puffing noise, especially when the engine is cold and first started. The sound often matches the engine’s RPM – it gets faster as you rev the engine. It might quiet down a bit as the exhaust heats up and metal expands, but it’s usually noticeable.
   
   
2. Sniff for the Smell: If you smell exhaust fumes inside or around your car, especially when idling or in traffic, that’s a major clue (and a potential health hazard!). It’s a strong, distinctive burnt smell. If you smell exhaust fumes inside your car, open the windows immediately and get it checked out! Carbon monoxide is deadly.
   
   
3. Look for Soot: As exhaust gas leaks out, it leaves behind black, powdery soot. Look for black discoloration around joints (like where the exhaust manifold meets the engine, or pipe connections), cracks in pipes or mufflers, or around gaskets.
   
   
4. The “Paper Test” (Use with Caution!): With the engine cold or only slightly warm (exhaust gets very hot!), start the engine. Carefully take a piece of paper, a rag, or even just your hand (don’t touch anything hot!) and move it near areas where you suspect a leak based on noise or soot. If there’s a leak, you’ll feel or see the paper/rag flutter or the exhaust puffs hitting your hand. Be extremely careful of hot exhaust components!
   
   
5. Use a Smoke machine: The easiest and quickest way to test for an exhaust leak is to use a smoke machine! I really recommend adding this tool to your DIY mechanic toolbox, I even have a guide to pick the best smoke machine HERE.

Common Spots for Leaks:

• Where the exhaust manifold bolts to the engine (manifold gasket leaks).
• Between sections of the exhaust pipe where they connect with clamps or flanges.
• Cracks in the exhaust pipes themselves, the muffler, or the catalytic converter.
• Around the O2 sensors, if they aren’t tightened correctly.

(I found a leak with the smoke machine in just 1 minute without using the jack!)

Spotting an exhaust leak early can save you headaches (and keep dangerous fumes out of your cabin). It’s a great example of using your senses for diagnosis!

P.S. I have a full DIY Mechanic video course (if you are a more video-visual learner), you can join HERE.