I have had an exhaust leak on my trusty Skoda for a while, I can hear it coming from miles away!
My problem was that to find the leak with the engine running was too difficult as the manifold and downpipe heated so quickly that I didn't have time to find the leak before everything was too hot to touch.
My solution, the mighty power of the humble vacuum!
WORDS OF WISDOM
1) Make sure the whole exhaust system is completely cold before starting work - I ended up quite ill after burning my hand on my friends exhaust many years ago.
2) Don't forget to disconnect the vacuum before starting the engine
(Photos by my 3 year old daughter Sennen)
Step 1: Connect the Vaccum Cleaner
This step is easy, just duck tape the pipe of the vacuum to the tail pipe of the exhaust and switch on.
I have used a Dyson cleaner which has an effective bypass valve to stop the motor overheating when the machine gets blocked. If you use a vacuum which does not have a good bypass, then you might need to make a deliberately leaky connection to the exhaust to stop the motor in the vacuum overheating.
Step 2: Find the Leaks
Now use a stethoscope (a funnel jammed in the end of a piece of flexible tube) to listen for leaks.
To find a leak play the open end of the hose as closely as you can over the exhaust system, paying particular attention to parts which might leak (Joints, flexible sections, etc.).
As you move the hose over a leak you will hear the nature of the hissing sound change.The suspected leak can then be confirmed by pressing your finger over the area and listening for the hissing to disappear.
Step 3: Leak Found!
Here is one leak - a pinhole in the weld where I had previously repaired the cracked manifold.
I had loads of leaks, leaking manifold, cracks in both flexible downpipes, a leak round the O2 sensor, leaking round the body of the cat and a massive leak where the front part of the system is joined to the rear.
(repairing the cracked manifold is another story)