Help! Riddle me this! What would make this noise. . .

[Bolisk]

Hello all!

I've been working on a project car for a while (72 big block). . .and when i finish running it. . .most of the time I would hear a gurgle hiss kind of noise. . .followed by a metal ticking / pinging noise for a few second (may be 15) after the car is shut off. The ticking / pining sound similar to the sound a hot car would make as it' cools off.

Anyway, I always assumed the noises were related to the hot engine cooling off. That is until this past weekend.

Over the weekend I began my engine leak down diagnostic, which requires that I turn the engine over by hand to test each cylinder. While turning the engine over by hand I heard the same damn noises. . .a hiss (without the gurgle) followed by a metal ticking / pinging noise!!! I want to point out that the engine was dead cold! I did not warm it up for the leak down test.

I will try to capture the noise on video later today.

-JR

 

[TimAT]

I'd suspect the "hiss" is compression escaping past the rings or valves after you stop turning it. Perfectly normal, unless you're having some rough running problems too. In a perfect world, the cylinder that stops at the top of the compression stroke would hold that compression until the piston moved or a valve opened. Real world- that's not going to happen.