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Technical FINDING VACUUM LEAKS the easy way

Discussion in 'The Hokey Ass Message Board' started by dare-to-be-different, Feb 25, 2018.

  1. I sometimes read about people asking advice how to find a vacuum leak.
    Almost always a common recommendation is to spray something flammable around the engine area that's suspected, and see if engine speed changes.
    I can't imagine that method working unless the leak is huge.
    Besides, I really really am cautious about creating a zone of flammable vapors and fumes around hot and possibly spark-inducing machinery.
    I stumbled across a few helpful hints for finding leaks the safe way that is far more effective than hoping the engine changes speeds.
    SOOO..... Here is a cheap device I made from spare junk laying around my used parts bins.
    A jelly jar, a soldering iron, some baby oil, and a little epoxy.
    Thats a wad of fiberglass cloth you see inside the jar to act as a wick to keep the soldering iron wet with baby oil.
    Voila le smoke generator.
    I blew smoke into the intake, or you could blow into the brake booster hose, and easily saw smoke signals coming from three hidden hose leaks that were making the engine idle rough.
    I found other ideas on Youtube. It made me wonder why it took me so long to actually do it.
    I think it cost about $5

    Just plug in the soldering iron, wait a minute or two for the smoke, plug almost any of the car vac lines to the jar, then blow on the other hose.
    Any well hidden vac leak will send smoke signals that are easy to spot.
    ...and you won't get a fireball from spraying too close to something... :)

    Oh yeah - P.S. That tape you see where the wire enters the soldering iron is to seal up a smoke leak when I blow into the system. I put rtv gasket sealer around the cord, then taped it so it wouldnt leak smoke when I blew in the hose :)

    Last edited: Feb 25, 2018
  2. Nice device,thanks.
  3. Cool. As I was trying to figure out what I was looking at and went back to reread, I had all my questions answered.........thanks for the edits, lol
  4. rgdavid
    Joined: Feb 3, 2014
    Posts: 274


    Good idea,
    Can make a "Lucas electrics replacement smoke generator" as well
    da34guy, czuch and '51 Norm like this.
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  5. 32v
    Joined: May 20, 2007
    Posts: 896

    from v.i.

    does your fan not blow the smoke every where
    rust runner likes this.
  6. Hemi Joel
    Joined: May 4, 2007
    Posts: 535

    Hemi Joel
    from Minnesota

    Apparently, you do this with the engine off. Neat trick!
  7. Jack E/NJ
    Joined: Mar 5, 2011
    Posts: 508

    Jack E/NJ
    from NJ

    Yeah, but I wanna know what happens when you inhale? Jack E/NJ
  8. We don't inhale,,,,,,,,,,,,,

    He said
  9. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 267


    Spray never worked for me either..

    I'd like to make something to come out the exhaust to get tailgaters off my bumper..
  10. Now it makes sense! I am going to try this, I have an annoying vac leak which whistles on idle, and this is after changing 3 throttle bodies!
  11. :) You have to pressurise it a tiny bit or the smoke won't want to come out.
    Some ppl use a low pressure regulated air hose at 1-2 lbs, some use a bicycle pump.
    I was about to use a harbor freight 6$ kayak bilge pump to push the smoke into the manifold, but simply blew on the hose, and that worked.

    brEad likes this.
  12. [​IMG]
  13. noboD
    Joined: Jan 29, 2004
    Posts: 6,584


    A handful of pastachios out the driver's window takes care of that. Sounds like a gun going of when it hits the windshield.
    Elcohaulic likes this.
  14. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 20,872

    Jalopy Joker

  15. Smoke um if ya got um. I like it!
    lothiandon1940 likes this.
  16. Reminds me of my nights in the HOOKAH bars in ancient Persia, thanks for the tip.:D;)
    chevy57dude, wraymen and MMM1693 like this.
  17. slowmotion
    Joined: Nov 21, 2011
    Posts: 2,921


    I can appreciate the engineering, but how about firing up a big ole, uh, Marsh-Wheeling, take a Bogart drag, and shotgun it into the vac-port on the intake for the same effect? :eek::D
    wraymen and lothiandon1940 like this.
  18. manyolcars
    Joined: Mar 30, 2001
    Posts: 7,500


    A container of automatic transmission oil mounted above the carburetor, with a hose going to the carburetor ought to do it. Dont remember which movie that was in
  19. blowby
    Joined: Dec 27, 2012
    Posts: 5,245

    from Nicasio Ca

    Excellent, thanks for posting! Gonna make one soon. You said "That's a wad of fiberglass cloth you see inside the jar to act as a wick to keep the soldering iron wet with baby oil". So it's a big balled up wad you poke the iron into? And how much oil, just enough to wet the cloth or some actually sitting at the bottom? I have olive oil, vegetable oil, motor oil, why baby oil?

    Thanks again!
    wraymen likes this.
  20. Baby oil is just scented mineral oil and it has a flash point of about 280 deg F.
    Canola or vegetable oil has a 621 deg F flash point but it also has a much higher smoke point of 500 deg F. Mineral oil's SP is 265 F and is used to make smoke in toy trains so it seems like a good candidate.
    Please experiment with the different oils and get back to us.;):)

    Edit: Just realized a 25 watt soldering iron can get above 400 F so now I'm totally confused.
    Last edited: Feb 27, 2018
    lothiandon1940 likes this.
  21. You will completely forget why you are doing it in the first place and go and get a snack.
    slowmotion and lothiandon1940 like this.
  22. slowmotion
    Joined: Nov 21, 2011
    Posts: 2,921


    Hey, don't want you guys to get the wrong idea:
    Btw, anybody else hungry?

    lothiandon1940, saltflats and wraymen like this.
  23. I'm not a cigar guy, had no clue. Can you tell I grew up in the 60's-70's.
  24. ..........C'mon mon, not this............:eek: hqdefault.jpg
    dan31, DIYGUY and wraymen like this.
    Joined: Jan 13, 2004
    Posts: 2,692


    OK ,I get it now ,thats what Cheech and Chong were doing in that 64 Chebby ,checking for vacumn leaks.
  26. rfraze
    Joined: May 23, 2012
    Posts: 1,977


    We used an oil can full of trans fluid with a small hose thru firewall, wired to top of carb. Get rolling, start with a pump of oil can to see how much smoke it makes. Go from there. It will be funny. You can make the rest of the world disappear, if you keep can keep the engine running. Do not hang around the area after.
    elgringo71 likes this.
  27. 5brown1
    Joined: Apr 13, 2008
    Posts: 163


    I built one and used it yesterday. Works great. Thanks for posting.
    wraymen likes this.
  28. I just now made another smoke machine because someone borrowed mine :)

    Here's a pic of what I do to make sure I get good contact between the baby oil and the heater.
    I buy a kerosene lamp wick from the camping section at Wal Mart, and wire it tightly to the soldering iron with a bit of picture hanging wire also from Wal Mart. That way I know the heater stays wet with oil, while the wet fiberglass wadding in the jar keeps the wick supplied with baby oil. I keep the wadding damp without a puddle.
    One wad of oiled glass fibers lasts a long long time without needing an actual oil puddle in the jar.
    Just simple wetness is the smokiest.
    We just finished tracking down several impossible-to-find obscure vacuum leaks in the strangest places on a smog-controlled rotary engined turbo Mazda, and it made a world of difference :)

    Like the guy said, baby oil has a low temperature smoke point, so it is easier to use, and you shouldn't need welding gloves to handle the bottle.


    Last edited: Apr 16, 2018
  29. blowby
    Joined: Dec 27, 2012
    Posts: 5,245

    from Nicasio Ca

    Got one done and it worked great on the bench, took it to the car and plugged it back in, nothing. The cheapo HF iron I bought won't even get warm now. Dang, all nicely glued in too.

    wraymen likes this.
  30. blowby is that jar full of oil? Might be too much.
    Last edited: Apr 24, 2018

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