I was just reading up here on Mobil oil about leak down tests. It
mentions something similar to what you did:
http://tinyurl.com/qh6sfzw

"Hearing problems
Beyond getting an overall picture of engine condition, the engine
leakdown test is an excellent way to pinpoint where problems are
before tearing down the engine. Listening for where the air is
escaping by ear can isolate the problem.

Intake valve : Air whistling out of the intake, carburetor or throttle
body indicates a leak at the intake valve.
Exhaust valve : Air heard hissing out of the tailpipe, turbocharger or
exhaust manifold means an exhaust valve leak.
Piston rings : Whistling or hissing out of the PCV valve, oil filler
cap hole or dipstick tube means the air is pushing past the rings.
Suspect ring or cylinder wall wear.
Head gasket : Air bubbles in engine coolant seen at the radiator
filler cap could mean air escaping into the coolant past the head
gasket.
Cracked cylinder head : Bubbles in coolant or coolant being pushed up
out of the radiator neck can also indicate cracks in the cylinder head
or cylinder walls."

On 5/3/15, Don Hanson <dhanson928@gmail.com> wrote:

>  ....I found the leak by
> removing the sparkplugs and putting air pressure into the pressure bottle
> of the cooling system...then I took a piece of conduit and listened
> carefully at each spark plug hole....found the leak, no problemo....

--
Neil n

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