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Crankcase pressure question

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Old Jan 10th, 2016, 22:35   #11
0151rhys
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Originally Posted by bournricha View Post
IT is perfectly fine ,there will be momentary pressure on speeding the engine .The vacuum afterwards shows the pcv is sucking out the fumes as it should .Main thing is you have not got smoke puffing out of the dipstick hole .
This is the strange thing I have smoke coming out of the dipstick and the finger on the glove inflate but under no great pressure. I have replaced the pcv but I am wondering if the port which the tank mounts by is blocked further down as it looked clear. I am guessing the filler cap area is okay as the pipe coming from the rocker cover is clear.
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Old Jan 11th, 2016, 08:54   #12
Brianjone5
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Originally Posted by 960kg View Post
At idle it is supposed to be + 2or3 kilopascal....not even .5psi.....but definitely on the plus.
' ... On the plus' - do you mean crankcase pressure? I thought it was supposed to be marginally less than atmospheric pressure, at idle. Do I have it wrong?

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Old Jan 11th, 2016, 15:17   #13
960kg
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All engines are pumps and have blowpast which = positive pressure

On a 4 cylinder two pistons up will give negative pressure counteracted by the two pistons down which give positive pressure....this plus the blowpast amount gives positive crankcase pressure at idle. Volvo being 5 cylinders the result is the same but slightly different.

The vacuum pipe connected to the inlet manifold for the crankcase ventilation is very low and not enough to create a full vacuum at idle because of the size of the sump but will develop a stronger vacuum upon engine speed to suck out the blowpast fumes also with the aid of the air being forced into the turbo near of which the PCV pipes exit into the airhose.

The old Fords had a pipe from the crankcase going down the side of the engine and the air rushing past the end of the metal tube caused a vacuum and the fumes were sucked out!

Light smoky fumes will come out the dipstick tube when idling and no dipstick in situ as the slightly plus crankcase pressure takes the least line of resistance and just comes out a hole instead of going along all those PCV pipes.

My `97 V70 T5 reacted exactly this same way when i replaced the PCV at 160,000mls. The engine was in superb condition.

The smoke or fumes is all normal but the amount depends how worn the engine is.

On one of my Lotus Cortinas the early engines had cast iron rings which wore quickly by 20/30,000mls and you changed them when oil squirted out of the dipstick tube...lol.......this is true!
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Old Jan 20th, 2016, 11:02   #14
Jaeger
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Default 2008 d5

As a matter of interest, does a 2008 V70 D5 have a pcv? 118k on the clock and inflates rubber glove slightly at idle.
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