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Old 11-24-2019, 05:32 PM   #1
dogsfoot68
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Default high vacuum when oil cap removed

I have noticed that when I remove the oil cap when at idle that there seems to be a lot of vacuum and the revs drop quite a bit. I also have a catch can on the PCV with a dip stick, same thing when I remove the dip stick there is a lot of vacuum and engine drops revs.
Is this normal behavior or is there something going on.
car seems to run fine but does have a surging feel when pushing it.
Mods are, TGV, EGR deletes, EBSC, charge pipe.
Also have occasional blue smoke at start up, could this be due to the high vacuum and turbo seal
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Old 11-25-2019, 09:24 AM   #2
dpetro1
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Default

My guess is that the pcv is pulling vacuum on the crankcase so by opening the oil cap you have effectively created a leak?
I don't think you have a problem.

Side note: why would you remove the oil cap with the car running?
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Old 11-25-2019, 10:13 AM   #3
scubaboo
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I had those exact symptoms, plus increased oil consumption, in another car. The PCV valve was clogged and had to be replaced.
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Old 11-26-2019, 06:14 PM   #4
dogsfoot68
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Quote:
Originally Posted by dpetro1 View Post
Side note: why would you remove the oil cap with the car running?
why wouldn`t you ? To check the health of the engine i guess....
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Old 12-03-2019, 03:01 PM   #5
3eyesraver
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Quote:
Originally Posted by dogsfoot68 View Post
why wouldn`t you ? To check the health of the engine i guess....
Isn't it the car a closed pressurized loop while running? My dad told me not to open the oil cap when the car is still hot.
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Old 12-03-2019, 07:02 PM   #6
dpetro1
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Quote:
Originally Posted by 3eyesraver View Post
Isn't it the car a closed pressurized loop while running? My dad told me not to open the oil cap when the car is still hot.
The crankcase (oil fill) is not pressurized with oil so you can open it while running/hot.
Radiator cap is a different story though...
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