How do you trace a small exhaust leak?

[Joe H]

I suspect I have a minor leak in the cat / flex / lambda boss / gasket area.
Trouble is that it gets so hot there that I cannot get my hand close enough to really check.
I have done the usual blocking exhaust with a rag and increasing revs but that just gets it hotter.
There is no obvious staining, cracking or holes so any tips for tracking it down (before removing)??

Cheers
Joe

[SwedishBus]

The normal method for doing this job is to use a leak-detection machine; basically a smoke-producing rig that pumps smoke from baby-oil (or similar) under very light pressure through a fitted bung. In this particular case, you would fit the bung in the exhaust tailpipe with the engine stopped and the system cold, and give the smoke machine a couple of minutes to fill the exhaust system, then any leak around the manifold area or backwards would be apparent.

Do you have a friendly local garage that has such a machine? They are fairly common (I use a Smoke Pro, but there are several types) and for the sake of a few minutes, it would give you an instant result.

Don't be tempted to try making your own smoke (like the internet says!!!) as you will either kill the catalyst, or kill yourself, in the process of using the wrong sort of smoke.

[Joe H]

You learn something new every day...I have never heard of that so thanks.
I will call into an exhaust place that should be open this evening and see if they have one.
Cheers
Joe

[Rebuild]

What I use is a shop vac. You can just set it to blow air and place the hose into the exhaust pipe. Then it's just a matter of feeling around the entire exhaust to find the leak, usually it's pretty obvious. Also what you can do is spray soapy water on the exhaust, bubbles forming = leak. Very much similar to finding leaks on a tire that way... some say doing it this way may force debris into the engine so it might not be the absolute best way to go about it...

[byootox]

I use the smoke pro as well, if the garage has one or equivalent get them to smoke the intake side as well.
Very useful tool for small leaks.

[Joe H]

Originally Posted by Joe H

I will call into an exhaust place that should be open this evening and see if they have one.
Cheers
Joe

Well....I got to the Independent exhaust place I last used a couple of years ago.
Made it all the way into the Reception before I realised they have been taken over by Kwik Fit!
Still, they stuck the car on the lift and using eyeballs and a mobile phone torch decided the lambda boss is leaking, although there was no real evidence of it.

I have applied a sticking plaster (GunGum) and am committed to the MOT test this afternoon so will see what that shows.
If necessary I will search out a place with some technology to do a better diagnosis.

Thanks all
Joe

[KBB]

Combination Smoke pro and Flir camera are my tools of choice.

[SwedishBus]

Originally Posted by KBB

Combination Smoke pro and Flir camera are my tools of choice.

Ditto. The FLIR has been one of my best investments for fast and accurate diagnosis of almost anything; leaks, blockages, air-locks, resistive electrical connections, faulty sensors, faulty air-con, etc.etc.

[canis]

Originally Posted by Joe H

Kwik Fit ... stuck the car on the lift and using eyeballs and a mobile phone torch decided the lambda boss is leaking, although there was no real evidence of it.

Please treat any Kwik-Fit diagnosis with extreme suspicion.

[Joe H]

Originally Posted by SwedishBus

Ditto. The FLIR has been one of my best investments for fast and accurate diagnosis of almost anything; leaks, blockages, air-locks, resistive electrical connections, faulty sensors, faulty air-con, etc.etc.

I love this forum. I would never have thought of using IR for dodgy electrical connections or air locks.
Joe