Smoke test vacuum system
Thread Starter
Advanced
Joined: Jan 2018
Posts: 57
Likes: 10
Smoke test vacuum system
I see this come up a few times when people are troubleshooting vacuum leaks..."do a smoke test". I would be interested to see how to do that. Anyone?
Last edited by cocodrillo; Dec 5, 2019 at 10:29 AM.
Pro
Joined: Nov 2019
Posts: 606
Likes: 55
From: Dover, Delaware
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
"Smoke" might work for a pressurized system; but smoke in a vacuum system would not come out of vacuum hoses or components. To the contrary, outside air would be ingested at the point of any leakage. The 'smoke' would go into the intake manifold to be blended with the fuel charge.
The best diagnostic method for a vacuum system is to isolate (plug/block off) a small portion/component/vacuum line and draw a vacuum on it, looking to see if the vacuum level decreases (indicates leakage).
The best diagnostic method for a vacuum system is to isolate (plug/block off) a small portion/component/vacuum line and draw a vacuum on it, looking to see if the vacuum level decreases (indicates leakage).
Last edited by 7T1vette; Dec 5, 2019 at 04:00 PM.
Burning Brakes
Joined: May 2013
Posts: 789
Likes: 129
From: Los Banos CA
You can google 'smoke machine for vacuum leak detection' - but here's a video that shows the basic process (but on a BMW):
All you need is a jar with a lid, something to burn that smokes (sock with some baby oil), and some sort of pump to force the smoke into the hoses. The video uses a soldering iron for the heat source ($4 at Harbor Freight) , and a bicycle tire pump, but I've also seen one that used the small orange transfer pump from Harbor Freight ($7). Since some of the vacuum circuits on our vettes are only active while the engine is running and switches in certain positions (you do the smoke test with the engine off), you'd have to check those hoses separately from the hoses attached to the engine.
Beware of check valves - as those only pass air one direction, and note that once smoke makes it to the inside of the intake manifold, it will come up thru the carb, so you might want to somehow seal the top of the carb. I've never done this on a carbureted vehicle, just saw it used once on a fuel injected car.
If you decide to make one, be sure to post up your results.
All you need is a jar with a lid, something to burn that smokes (sock with some baby oil), and some sort of pump to force the smoke into the hoses. The video uses a soldering iron for the heat source ($4 at Harbor Freight) , and a bicycle tire pump, but I've also seen one that used the small orange transfer pump from Harbor Freight ($7). Since some of the vacuum circuits on our vettes are only active while the engine is running and switches in certain positions (you do the smoke test with the engine off), you'd have to check those hoses separately from the hoses attached to the engine.
Beware of check valves - as those only pass air one direction, and note that once smoke makes it to the inside of the intake manifold, it will come up thru the carb, so you might want to somehow seal the top of the carb. I've never done this on a carbureted vehicle, just saw it used once on a fuel injected car.
If you decide to make one, be sure to post up your results.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
I just use an unlit propane torch.......as soon as vacuum sucks in the propane, the idle will change. Much easier.
I do this on vintage Japanese bikes too......the propane sniffs out leaks on a multi carb like nobodies business.
Jebby
I do this on vintage Japanese bikes too......the propane sniffs out leaks on a multi carb like nobodies business.
Jebby
Last edited by Jebbysan; Dec 5, 2019 at 05:07 PM.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
The whole idea of smoke test is to look for an area that will indeed suck the smoke in. Such as under a carb, Intake gaskets, Vac hoses etc. If the smoke is drawn in somewhere, there is your leak.
This smoke test, like the propane bottle or starter fluid spray test is usually hindered by the wind from the fan blowing over the entire engine. For a true test, the fan belts should be removed, just briefly of course.
This smoke test, like the propane bottle or starter fluid spray test is usually hindered by the wind from the fan blowing over the entire engine. For a true test, the fan belts should be removed, just briefly of course.
Burning Brakes
Joined: May 2013
Posts: 789
Likes: 129
From: Los Banos CA
The whole idea of smoke test is to look for an area that will indeed suck the smoke in. Such as under a carb, Intake gaskets, Vac hoses etc. If the smoke is drawn in somewhere, there is your leak.
This smoke test, like the propane bottle or starter fluid spray test is usually hindered by the wind from the fan blowing over the entire engine. For a true test, the fan belts should be removed, just briefly of course.
This smoke test, like the propane bottle or starter fluid spray test is usually hindered by the wind from the fan blowing over the entire engine. For a true test, the fan belts should be removed, just briefly of course.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Ok, gotcha. The ones I saw had a pin point smoke gun and you aim it at suspected vacuum leak areas with engine running. (But the fans force gave poor results).
Similar to the type used to check for cold drafts in houses.
Similar to the type used to check for cold drafts in houses.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Lots easier to spray some carb cleaner (little puffs only) at an area in the vacuum system on a running vehicle (as mentioned above). Engine will rev if any of that vapor is sucked into a 'venting' crack/brake/tear/hole/leak-path. That will work for any vacuum system item that is directly connected to the intake manifold and/or carb base plate.
The smoke method may work on system with non-running engine; but I'd prefer to test isolated sections of a 'problem' system using a hand-held vacuum pump.
The smoke method may work on system with non-running engine; but I'd prefer to test isolated sections of a 'problem' system using a hand-held vacuum pump.
Last edited by 7T1vette; Dec 5, 2019 at 11:26 PM.
