Find an Exhaust Leak Without Burning Your Hands!




Introduction: Find an Exhaust Leak Without Burning Your Hands!

I am Married to Beth, I am an Architect and have four wonderful children

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!

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)



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    29 Discussions

    This is extremely dangerous idea as you will likely suck fuel fumes into the vacuum cleaner (I haven't seen any domestic or shop vacs with brushless motors yet so they will have sparks) that will ignite and set the vacuum cleaner on fire and then possibly your car. It is a 4 stoke engine after all so one of the cylinder at least will be on the compression stroke when the engine stopped (post fuel injection but pre ignition). There will also be some combustible blow-by gas in the crank case that will be drawn out by the vacuum. If there is some other undiagnosed issue such as a dribbling injector (or leaking carburettor) the risk is even greater. You'll get away with it 80% of the time but the other 20% of the times will end catastrophically and may even get you a Darwin Award.

    1 reply

    You are correct. I just posted the same thing and then did a word search and found yours. These guys are headed for the ER. Good catch.

    Great instructable! I used my shop vac to blow air into the tailpipe of my Ford F350-- then I sprayed soapy solution all over the joints and found leaks easily without having to run the engine. Thanks

    The easy way go to shop and get a big bottle of shampoo and conditioner mix together no water you want it thick get a brush start car and start brushing it over areas and you will see bubbles and air leak then switch car of after it gets to hot Let it cool down try again working down works well

    1 reply

    In my case i couldn't reach the part of the engine with the leak from below without removing the EGR cooler (which is part of the exhaust system, so can't do that) or from above without removing the majority of my air intake.

    Without the air intake, i can't safely start the engine, but i can still externally pressurize (or depressurize) the exhaust and listen for leaks. This was definitely easier than the afternoon i spent with soap and exhaust fumes.

    Worked like a charm. Found a pesky leak in just a couple of minutes.

    I had tried soap first, but the leak was in a spot that i couldn't access with a mirror or my hand until i had removed most of the intake piping and no way I'm running my engine without an air filter!

    I agree with Ross that it would be better to use a shop vac to blow air in, but of the car has sat overnight most of the combustibles should have dissipated. Still, place a fire extinguisher and a helper near the vacuum to keep a close eye on it.

    Er du dansker?

    This was just brilliant. I was able to isolate that pesky leak in less than 10 minutes. Thank you very much!

    Thanks for the great tip!! I decided to use my vacuum's blower function instead and just felt/listened for blowing air. I would guess if you weren't careful the blowing air could cause some ear damage, but that's why we're careful! This was so much better than having someone rev the engine while I listened and felt around for hot air blowing out.

    Wonderful idea! I was going to use my party smoke machine shoved in the tailpipe to check for leaks (similar to smoke generators mechanics might use), but this is a good alternative.

    i think you can also use a manual air pump to blow in , of course with the use of the washing up liquid. i wonder if just by obstructing the exhaust, it can create a pressure to obtain a good clue where to concentrate your attention.

    New downpipe for most of the holes, but a little bit of welding on the manifold.
    (I do the welding with the engine hot (not running because you need to disconnect the electrics) and this helps to avoid heat stress cracking around the weld)

    IIRC cast iron is tough to weld. They usually do a pre-heat with torches and hammer on the weld while it cools. Also, there's a special type of arc electrode for cast iron that is expensive because of a high nickel content.

    Yes the main trick with cast iron is to pre-heat (blow-lamp or bake - this is what getting the exhaust up to temperature does) and then cool slowly - often burying in sand or wrapping up. I have done a bit of cast iron welding, repairing an old wood-burning stove and the manifold and it seems to work OK.
    I don't have a special electrode - I just use my MIG welder with standard steel wire

    Using the engine to preheat is an outstanding idea, BTW.  This way there is residue heat throughout the entire casting which should allow it to cool slowly.

    I'm sure the special rod is more critical when fixing a large crack or split.

    For a hole, I wonder if drilling, and then tapping a hole might work?

    I don't see why it shouldn't - you sometimes see plugged holes on manifolds anyway as part of the design - you could lubricate the threads with a bit of exhaust assembly paste