[AT] propane to detect vacuum leaks.

[Stephen Offiler]

If you need the information provided in Step 1, just close the hood and
walk away.

SO

On Tue, Oct 29, 2019 at 12:04 PM James Peck <jamesgpeck at hotmail.com> wrote:

> Here is a post outlining the procedure for vacuum leak testing with
> propane.
>
> https://www.hunker.com/13414896/how-to-find-a-vacuum-leak-with-propane
>
> 48 years ago a man taught me how to use a vacuum gauge in diagnosing a
> blown head gasket.
>
> I will have to remember Stephens tip for using propane on hard starting
> gasoline engines.
>
> [Jack] If a bare plug wire were sparking to ground it could light the
> propane torch if you moved the torch nozzle so propane flowed over the
> spark. A bare plug wire itself would not heat propane to its ignition
> point.  The torch itself restricts the propane flow.
>
> However, the only engines I have encountered with hard to find engine
> vacuum leaks are V6 and V8s where the intake manifold seals against both
> the block and heads. You can’t usually see the rear manifold seals and they
> do get out of place. Tractor spark ignited engines are generally straight
> 4s and 6s.  I suspect that the use of propane to find vacuum leaks dates to
> the introduction of the OHV (overhead valve) V8.
>
> We did have a flathead Ford V8 on a piece of equipment when I was a kid.
>
> I once had a pinhole leak in an anti-dieseling pneumatic damper diaphragm
> that I found using a handheld vacuum device. This was on a vehicle without
> ECM (engine control module).
>
> [Jim Becker] I’ve wondered how often that method accidentally finds a plug
> wire with bad insulation.
>
> [Jack] In the automotive courses I took, we would use an unlit propane
> torch and direct the gas flow over spark ignited engine areas of possible
> vacuum leaks. If the engine speed increased, you had found the leak.
>
> [Stephen Offiler] Anybody use propane/MAPP?  Unlit torch pointing into the
> air box.  I use it on reluctant gasoline engines with a fair amount of
> success, but not so sure about diesel.  Since we're talking about
> gas-soaked rags or gas-soaked air filters on diesel engines, seems like a
> similar approach.
>
> .
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