Picture of Find an exhaust leak without burning your hands!

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

Picture of 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.
Dogswar1013 months ago
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
gerike 4 months ago
Er du dansker?
E.PLUMBUSU8 months ago

This is an excellent idea.

ken.faul.18 months ago

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

hamsammy1 year ago

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.

Monty^1 year ago

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.

ooilpond2 years ago
Clever Bugga!
chekespeare3 years ago
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.
DIY Dave4 years ago
Now how do you patch the hole?
PeterTheUnGreat (author)  DIY Dave4 years ago
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)
I never would have thought to weld with the engine hot.
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.
PeterTheUnGreat (author)  kill-a-watt4 years ago
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?
PeterTheUnGreat (author)  kill-a-watt4 years ago
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
classtopher4 years ago
Great post. Would it be a bad idea to use a shop vac and blow air into the tailpipe? I dont know if this would be bad for the catalytic converter or not. But if you did that then you could simple feel the leaks with your hand and probably wouldn't need the funnel contraption.
PeterTheUnGreat (author)  classtopher4 years ago
You could try blowing - I couldn't do that because the Dyson doesn’t have a blowing attachment.
I don't think you would be able to find the tiny leaks just by feeling, but you could try a bit of washing up liquid and look for bubbles
Chrislee4 years ago
Thank you for your genius. I'm gonna use Mighty Putty. They won't have this
noisy 'ol lady to kick around anymore!
JuCo4 years ago
cool idea. and i love everything about the "car doctor" picture.
aaahotdog4 years ago
Very good idea
jeff-o4 years ago
Great tip! Thanks very much.
pfred24 years ago
Pretty good idea. I use welding gloves, when I am over the leak it gets muffled so to speak.
Babyshoes4 years ago
I must admit I was skeptical when I read your title, but this is a clever way for someone to check for leaks at home.
zazenergy4 years ago
Awesome! This is so handy!