TheSamba.com :: View topic - Finding vacuum leaks with smoke (smoke test, tester)

Mon Feb 23, 2015 7:28 pm

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Hi all,

A quick write up for this forum, since I couldn't find it when I was searching earlier. I recently had some vacuum leak woes. I built a smoker to make it easier to find them. Based on this design over in the Vanagon forum: http://www.thesamba.com/vw/forum/viewtopic.php?p=5282178

Parts required:
- Quart paint can
- 1/8" barbed to NPT fitting
- Valve stem
- JB weld, epoxy, something gluey.

Instructions:
1) Drill two holes in the lid, one for the barbed fitting, one for the valve stem.
2) Insert barbed fitting, pot with epoxy or JB weld.
3) Install Valve stem

To use:
1) Hook up a pump to the valve stem (I used a manual bike pump).
2) Hook up a vacuum line from the barbed fitting to a place in the vacuum system.
3) Block S-boot with a beer bottle.
4) Light something on fire in the can. I used a scrap of t-shirt soaked in gas and oil, along with some cardboard.
5) Put the fire out, pop the lid on, start pumping the air pump and look for smoke.

Relevant pictures below:

GoBigEmma wrote:
That's a cool setup! We copied it to check for vacuum leaks, but we used smoke bombs that I used to make as a kid instead of cigarettes: Wrap a ping pong ball in aluminum foil (make sure to wrap it tight or it will burn, but not smoke) and hold a flame under one spot of it until it starts smoking. Produces a whole lot of smoke (like, A LOT), but breathing that stuff in definitely shortens your life by the smell of it, so be careful. :-)

Mon Feb 23, 2015 7:46 pm

I've always found starter fluid to be very sensitive but I hear unlit propane from your torch works well too. In a few situations I've found leaks with vaseline.

What's the advantage of building a smoker?

Mon Feb 23, 2015 7:58 pm

I tried the propane torch trick, it didn't work very well for me. I wasn't a fan of spraying starter fluid on my freshly cleaned and painted engine, so I built the smoker. Worked really well so far for me, and for ~$10 I have a new tool for diagnosing. I'll probably add smoking the vacuum lines to my tune up list just because it's easy to do and keep the FI system happy.

Mon Feb 23, 2015 8:08 pm

sixer wrote: I tried the propane torch trick, it didn't work very well for me. I wasn't a fan of spraying starter fluid on my freshly cleaned and painted engine, so I built the smoker. Worked really well so far for me, and for ~$10 I have a new tool for diagnosing. I'll probably add smoking the vacuum lines to my tune up list just because it's easy to do and keep the FI system happy.

Gotcha.

For $4.00 I got a pack of camels and a rubber hose. :D

Mon Feb 23, 2015 8:36 pm

http://www.thesamba.com/vw/forum/viewtopic.php?t=599295&highlight=smoke+cigar

Tue Feb 24, 2015 6:52 am

I do the opposite. soap everything, pressurize the air intake to 2 PSI, watch the bubbles.

can't bring myself to fill the engine compartment with propane and generate sparks. downright Darwinian.

Tue Feb 24, 2015 10:04 am

Smoke and propane are not capable of finding really small/fine vacuum leaks....especially the type that, open up larger with heat expansion and vibration.

Typically these are very thin leaks less than .001" in space ...on items like runner boots and flat intake runner seals etc.

These types of leaks are rarely large by themselves. Its usually several of them creating a cumulative leakage......which fuel injected systems are very sensitive too. Usually finding these types of leaks is the final stage in really fine tuning.

There is usually either not enough airflow through these leaks or not at the time and rpm you are testing.....which is why smoke and propane do not work In these cases.

However smoke and propane work well on cracked hoses, fittings etc.

Solvents like carb cleaner work well on the types of leaks that smoke does not work on because.....its thin enough to get into crevices and highly flammable. However its also hard on paint and coating.

If you have time a very thin machine oil in a dripped bottle for checking seals you suspect can work well. In some cases.....just soap water works well as others have noted.

You need to use soap to break the surface tension or the water so it gets into very narrow leaks. You can also use Jet-Dry for dishwashers. Mixed with water it makes a good leak checking liquid. Ray

Wed Sep 16, 2015 7:51 am

windex often will turn up a leak without stripping paint off.

Wed Sep 16, 2015 9:34 am

Mal evolent wrote: I do the opposite. soap everything, pressurize the air intake to 2 PSI, watch the bubbles.

This is a great way to do it. Because you are under positive pressure. Leaks that may close up under negative vacuum open up.
For when soap and water won't cut it.
Tire Leak Detectors SPC 35805

Good day
Tcash

Tue Dec 08, 2015 8:48 am

situation,, engine won't start,, looked like crazy for a vac leak.. can't find it.. blow smoke thru into the intake... and see it coming out under the front wheel !! holy crow.. the vac hose is bust at the brake booster.

:idea: I am thinking out loud.. but a bicycle tube , cut to appear to be a hose.. one end stretched over the S boot... and the other end on the smoke source.. lol.. I don't know if you can take a big TOKE on see gar,, and Huff it enough to make it fill the intake system enough to appear thru a leak... but I guess if the leak is right there,, and big enough.. it might just work.. otherwise a vacuum cleaner might add enough blow to make the smoke rise

:idea: you tube has plenty of cheap home made cigar smoke machines to let you adapt ..

Mon Mar 14, 2016 5:15 am

Just a bump for this helpful thread and a big thanks to OP. Built one of these and found 2 small leaks. Tool cost me about $10 to build and I fixed the leaks with $3 in hose clamps! My bus idles better now.

One tip for others, a 12V air mattress pump works perfectly and you can run it right off the battery of course. A completely portable vacuum leak tester :wink:

Tue Jun 28, 2016 7:19 am

I am about to build this handy contraption but had a few questions.

I assume you look for leaks with the engine OFF? Plug S boot and then introduce the smoke to ANY of the vacuum lines? The smoke will then leak out of wherever the leak is, correct?

Sometimes I have a hard time visualizing things. So thank you!

Tue Jun 28, 2016 7:24 am

engine off. You are looking where smoke escapes.

Tue Jun 28, 2016 8:51 am

busmania wrote: I am about to build this handy contraption but had a few questions.

I assume you look for leaks with the engine OFF? Plug S boot and then introduce the smoke to ANY of the vacuum lines? The smoke will then leak out of wherever the leak is, correct?

Sometimes I have a hard time visualizing things. So thank you!

https://www.youtube.com/results?search_query=smoke+test+vacuum+leak

Tue Jun 28, 2016 11:58 am

Tcash wrote: busmania wrote: I am about to build this handy contraption but had a few questions.

I assume you look for leaks with the engine OFF? Plug S boot and then introduce the smoke to ANY of the vacuum lines? The smoke will then leak out of wherever the leak is, correct?

Sometimes I have a hard time visualizing things. So thank you!

https://www.youtube.com/results?search_query=smoke+test+vacuum+leak

As a visual learner, this helps a ton. thank you.

Now when my wife is mad because I'm in the garage "smoking" cigarettes (I quit years ago), i'll point her to the home made red neck smoke machine video.

https://www.youtube.com/watch?v=rumgJ5UBpCw

Thanks again.

Wed Jun 29, 2016 7:09 pm

sixer wrote: I recently had some vacuum leak woes. I built a smoker to make it easier to find them.

That's a cool setup! We copied it to check for vacuum leaks, but we used smoke bombs that I used to make as a kid instead of cigarettes: Wrap a ping pong ball in aluminum foil (make sure to wrap it tight or it will burn, but not smoke) and hold a flame under one spot of it until it starts smoking. Produces a whole lot of smoke (like, A LOT), but breathing that stuff in definitely shortens your life by the smell of it, so be careful. :-)

Mon Aug 29, 2016 6:02 pm

GoBigEmma wrote: sixer wrote: I recently had some vacuum leak woes. I built a smoker to make it easier to find them.

That's a cool setup! We copied it to check for vacuum leaks, but we used smoke bombs that I used to make as a kid instead of cigarettes: Wrap a ping pong ball in aluminum foil (make sure to wrap it tight or it will burn, but not smoke) and hold a flame under one spot of it until it starts smoking. Produces a whole lot of smoke (like, A LOT), but breathing that stuff in definitely shortens your life by the smell of it, so be careful. :-)

I don't even remember why I'm looking at this thread, but Eureka! Smoke Bombs, Brilliant! I can get those year round in TN. You may not even need to add air pressure with those.Thank you GoBigEmma! I'll have to try it just because...

Tue Dec 12, 2017 9:03 pm

So, how would I do a vacuum test using a smoker when I have carbs?

I'm guessing I can blow the smoke through the hose used for vac to the booster?

What do I need to cap off, and how?

Wed Dec 13, 2017 12:48 am

Terminatez wrote: So, how would I do a vacuum test using a smoker when I have carbs?

I'm guessing I can blow the smoke through the hose used for vac to the booster?

What do I need to cap off, and how?

Nitrile or latex work gloves work well as blockers on carb intakes,
they tend to snap right over modern throttle bodies but you can tear a palm
shaped piece out of one & use a rubber band or air filter clamp/zip tie
to seal carb throat. If you are running an open breather set up, plug that as well. Booster line is where I usually stuff the smoke.

Wed Dec 13, 2017 12:48 pm

Cap the exhaust pipe too. Remember, when you find the first leak plug it anyway you can and keep going, finding and plugging, until you find ALL the leaks. Don't forget to check around your exhaust system too