Precisely locating an exhaust leak determines how it best can be sealed. Typical exhaust systems are clamped or welded at vital connection points. The nature of the exhaust system and the overall condition of the system determines when leaks can be sealed and when replacement parts must be installed. Wear safety glasses to prevent rust and dust associated with exhaust pipes from entering your eyes. Inspect for exhaust leaks with the vehicle running in a well-ventilated area.
Inspect under the hood where the exhaust manifold meets the engine block. Look for soot or burnt paint. Listen for hissing or popping noises, and inspect the manifold for cracks. Either replace the manifold gasket or if the manifold is cracked, replace the manifold itself.
Inspect where the manifold or header meets the exhaust pipe. A round graphite gasket often seals the exhaust at this joint. Look for soot, feel for hot gases, and listen for noise around the joint. Replace the gasket, if needed.
Turn on a flashlight and use it to examine the exhaust pipe under the vehicle, starting at the front and moving toward the rear bumper. Scrape rusty spots using the screwdriver to see if rust goes through the pipe, or is just on the surface. For large rusty areas use the joint pliers and attempt to gently "squish" the pipe. If it bends under light pressure, replace that section. If only a small hole is present, wrap muffler tape around the pipe, covering the hole to seal the leak.
Inspect the joints where pipe meets the catalytic converter and muffler. Listen for noises, and feel for hot gases. Test clamps for tightness if clamped, and replace rusted clamps if necessary. Inspect welds if welded, and test the integrity of the pipe on both sides of the component before attempting to reweld.
Inspect the components themselves. If a catalytic converter or muffler has a hole in it, replace it. Most often, attempts at repairing these components are expensive and unsuccessful. Ensure that all clamps and hangers are tight, and reinspect for leaks after installation of new components.
Carbon Dioxide is a highly poisonous gas. Work in a well-ventilated area, and avoid breathing exhaust directly. Pay special attention to exhaust leaks under the hood. These can result in driver drowsiness or even death.