Checking for vacuum leaks

[BIG JACK]

Guys, I watched The Shadetree Mechanic tv show several years back and they were checking for vacuun leaks. They hooked a hose up to a propane torch (did not light it) and shot propane around all possible vacuum leaks. The engine would increase speed when a leak was found. Is this a good idea for oxygen sensors? Does this method work? Thanks.

 

[Maniak]

I never used the propane method, but I've used Carb Cleaner. The Carb cleaner I used is 02 sensor safe (not for this reason, just happens to be what I had). I spray around and if I find a vacuum leak the rpms change.

I also used this method to find a leak on a carb on the Van.. I had a leak right on the side of the carb.

Use the straw that comes with it though.. If you spray enough and the vapors make it into the engine (the normal way air goes in) then the rpms will change even though its not a vacuum leak.

~Mark

 

[BrianCollins]

Explosion Risk?

I would think that spraying propane to check for a vacuum leak would be rather dangerous. Might find a plug wire leak (with disastrous results) before you have a chance to find a vacuum leak!

 

[Turdle]

I always recommend using an unlit propane torch to search for a vacuum leak. Works great, and the gasses go right away, no fear of ignition. To me this seems better and safer than squirting fluid all over the place. Propane goes right away, but the liquid will hang around for a while. I see this as a greater concern for ignition than propane would cause. Plus, carb cleaner isn't very friendly to painted surfaces. LPG will not harm the 02 sensors.

Sometimes the cooling fan creates too much air movement and will blow the gas off course, so I remove the fan for more accurate "testing".

 

[ZWilson07]

Guys you all probably should check the thread before replying. I don't even know how you all randomly came across this thread lol.

This thread was over 5 years old!

 

[PAExplorerXLT]

Yes, but the problem persists. The propane method sounds good until you try it. The engine bay is so crammed with hoses and what not that is very difficult to get the nozzle anywhere close to where the leak might be at. Even if you do sense a change in rpm, you don’t necessarily know where the source of the leak is. Even my mechanic gave up on mine.

 

[96eb96]

1) Carb cleaner is scarier than propane. It is extremely flammable, maybe moreso than propane. Useless technique for some leaks.
2) RPM change would require a decent sized leak, better to monitor with a scan tool(fuel trim).
3) A smoke machine is a great tool as well. Smoke the intake and see where it comes out.

 

[PAExplorerXLT]

3) A smoke machine is a great tool as well. Smoke the intake and see where it comes out.

But isn’t that somewhat tricky too? You might see smoke but where it is coming out of may not be obvious.

 

[96eb96]

But isn’t that somewhat tricky too? You might see smoke but where it is coming out of may not be obvious.

Don't always work either. Some leaks happen at a certain engine temperature. Usually you get a good clue though from smoke.

 

[PAExplorerXLT]

Don't always work either. Some leaks happen at a certain engine temperature. Usually you get a good clue though from smoke.

There are also other clues. For example, my suspected vacuum leak only manifests itself at start up and in cold weather. After warm up it goes away. Does this limit the leak to a gasket? You would think if it was somewhere else, it would alway be there.