Crankcase under vacuum producing whirring sound until dipstick is removed?
12-29-2009, 11:07 AM
#1
Crankcase under vacuum producing whirring sound until dipstick is removed? Engine makes whirring or whistling sound. Couldn't pinpoint sound with mechanics stethoscope. Pulled dipstick. Sound disappeared. When I put my finger on dipstick tube it is sucked onto the tube. I know this is backwards, but the crankcase is under vacuum somehow. No driveability issures. How can I have vacuum in the crankcase? Where should I start looking as the source of this vacuum?
12-29-2009, 12:54 PM
#3
I know Positive Crankcase pressure has to escape somewhere, but this is negative crankcase pressure(vacuum). I know the PCV is connected to the intake helping evacuate the positive pressure in the crankcase, but does it switch from being positive pressure to being a vacuum? Look at all the cases of people with LS series engines that have their dipstick blown out. That's due to positive pressure not vacuum. Does this sound like a leaking gasket or cracked rubber hose? There is no fluid leaking and the engine runs properly.
12-29-2009, 12:59 PM
#4
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the PCV system pulls vacuum in the crankcase!!! that's how it sucks the nasty vapors out of the case.
not sure what they refer to when they call it "positive crankcase ventilation"....but the point of the system is to pull vacuum. my guess is to releive the "positive" pressure cause by blowby.
guys who have dipsticks blown out generally have removed the PCV and are running breathers...or are idiots and are NOT running breathers. hence they build pressure
not sure what they refer to when they call it "positive crankcase ventilation"....but the point of the system is to pull vacuum. my guess is to releive the "positive" pressure cause by blowby.
guys who have dipsticks blown out generally have removed the PCV and are running breathers...or are idiots and are NOT running breathers. hence they build pressure
12-29-2009, 01:09 PM
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here is a diagram of the stock pcv system on the ls1 (not the ls6 system).
as you can see the blue lines are pulling air out of the crankcase. by removing the dipstick would give another means by which to allow air to be pulled in...hence the sucking you feel.
is your PCV system hooked up right? if the clean air inlet is plugged...it would explain why its whistling to draw air in other places...and creating so much suction at the dipstick.
as you can see the blue lines are pulling air out of the crankcase. by removing the dipstick would give another means by which to allow air to be pulled in...hence the sucking you feel.
is your PCV system hooked up right? if the clean air inlet is plugged...it would explain why its whistling to draw air in other places...and creating so much suction at the dipstick.
01-01-2010, 08:01 AM
#6
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Your clean air supply is plugged and your setup is looking for another source to draw from (the dipstick when you remove it). If you pull the line off the passenger valve cover and the port on the cover sucks your finger like the dipstick removal does then the problem is between the cover and throttlebody.The line from the throttle body to the passenger valve cover (F body) should be checked as well as the actual port on the throttle body. At idle the PCV system draws more volume of air out of the crankcase than what gets forced into the crankcase from blowby.
As lame as this sounds I was able to build my entire motor from the bare block on and yet did not fully understand the PCV systems workings until recently.
As lame as this sounds I was able to build my entire motor from the bare block on and yet did not fully understand the PCV systems workings until recently.
