It's the only thing I could think of. 
Hissing while turning engine over by hand?
Hissing while turning engine over by hand? Did some valve work tonight and noticed a hissing sound when turning the engine over by hand. Sounds like air leaking or something as if pressure is being released. After turning the motor lets say 20 degrees, it will hiss for 3-5 seconds. The hissing is coming from the driver side only near the rear. Passenger side was dead silent. It hisses even with all spark plugs on the driver side removed which I thought was weird. Driver side rockers on or off, it still hisses.
I probably did about 4 full crank rotations by hand and the hissing never stopped or lessened. It's like somehow pressure is building in the cylinders even though the plugs are out. The plugs were still in on the passenger side, but how could pressure over there make a noise on the rear driver's side?
I can't think of anything back here that would cause this sound. I've been trying to track down a metallic tapping sound around cylinders 5-7, same area where this sound is coming from. Perhaps they are related?
I probably did about 4 full crank rotations by hand and the hissing never stopped or lessened. It's like somehow pressure is building in the cylinders even though the plugs are out. The plugs were still in on the passenger side, but how could pressure over there make a noise on the rear driver's side?
I can't think of anything back here that would cause this sound. I've been trying to track down a metallic tapping sound around cylinders 5-7, same area where this sound is coming from. Perhaps they are related?
Last edited by Ferocity02; Nov 16, 2012 at 12:55 AM.
Just came up with a theory actually. The passenger side might just be sucking in air through the PCV valve, which is located as the back of the drivers side on a 5.3L. I shall investigate tomorrow.
Figured it out... wasn't the PCV. But rather the hissing sound caused by the air leaking past the rings on bank 2 was going through the block and coming out of the head on bank 1 where I had the valve cover remove. I pulled the valve cover on bank 2 and heard the same hissing sound 
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Verdad Gallardo My only difference is that my engine is a fresh rebuild and does not hiss when the plugs are pulled and hooking up the starter to a batter with jumper cables will not turn the engine over with the spark plugs in
TECH Junkie
Joined: May 2012
Posts: 3,047
Likes: 714
From: Poplarville, MS
It will not hiss with the spark plugs removed because the compression is going out the spark plug holes. Can you turn the crankshaft with some type of wrench? If the crankshaft rotates with not a lot of effort your starter is defective, your battery is weak or not fully charged or your jumper cables are too small.
Its normal for the engine to "hiss" when the plugs are in it. ALL engines do this. Its the compressed air getting past the rings. Completely normal. Move along, nothing to see here.
Launching!
Joined: Aug 2014
Posts: 237
Likes: 2
Same happens when you turn over a small engine by hand. Have a 12HP Briggs on an old riding mower that does this.
