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Oil flow and Vehicle start with oil cap off. #5138985
06/20/19 06:49 AM
06/20/19 06:49 AM
Joined: Apr 2010
Posts: 3,585
Atlanta,GA
BMWTurboDzl Offline OP
BMWTurboDzl  Offline OP

Joined: Apr 2010
Posts: 3,585
Atlanta,GA
(deleted)

Last edited by BMWTurboDzl; 06/20/19 07:05 AM.

“It took untold generations to get you where you are. A little gratitude might be in order. If you’re going to insist on bending the world to your way, you better have your reasons.”

435i
Re: Oil flow and Vehicle start with oil cap off. [Re: BMWTurboDzl] #5138993
06/20/19 07:04 AM
06/20/19 07:04 AM
Joined: Nov 2008
Posts: 13,993
NH
supton Offline
supton  Offline

Joined: Nov 2008
Posts: 13,993
NH
I wouldn't think so... When one piston is going down (causing positive pressure) one is going up (negative pressure) so I don't think there is a net change in airflow in the engine. [At least when there is an even number of pistons, err at least in most conventional automotive engines.]
Likewise, when the engine lifts oil up and fills the galleries, the oil level drops in the pan.

Ultimately there is a ventilation system for the crankcase. This is to deal with blowby that is created while running.

Lastly, whenever I have removed the filler cap while running I've always had some amount of oil spray coming out and all over. Not a geyser mind you just enough to realize it's making a mess. Maybe that was just on the mills I've dealt with, maybe a BMW has better baffles.

In this case I don't think it will matter at all if you are just priming it, but that's my wild guess of the morning. Will be curious what the BMW mechanics have to say.


2011 Toyota Camry, base, 2.5L/6MT, 187k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 152k, ours
1999 Toyota Camry LE, 2.2L/4AT, 208k, his
Re: Oil flow and Vehicle start with oil cap off. [Re: BMWTurboDzl] #5138998
06/20/19 07:09 AM
06/20/19 07:09 AM
Joined: Dec 2002
Posts: 43,190
'Stralia
Shannow Offline
Shannow  Offline

Joined: Dec 2002
Posts: 43,190
'Stralia
Missed the OP...but read the second...

The swept volume of an automotive cylinder is not a pure sinusoidal volume change.

For exactly the same reasons that you can't balance a 4 cylinder, there is a significant change in crankcase volume every 90 degrees, and a change in pressure...leave the oil cap off a running 4 cylinder and have a look...

And there's not enough to change any sort of priming mechanism post oil change.


If it's the truth....it can handle the pressure !!!
Re: Oil flow and Vehicle start with oil cap off. [Re: Shannow] #5139003
06/20/19 07:19 AM
06/20/19 07:19 AM
Joined: Apr 2010
Posts: 3,585
Atlanta,GA
BMWTurboDzl Offline OP
BMWTurboDzl  Offline OP

Joined: Apr 2010
Posts: 3,585
Atlanta,GA
Originally Posted by supton
I wouldn't think so... When one piston is going down (causing positive pressure) one is going up (negative pressure) so I don't think there is a net change in airflow in the engine. [At least when there is an even number of pistons, err at least in most conventional automotive engines.]
Likewise, when the engine lifts oil up and fills the galleries, the oil level drops in the pan.

Ultimately there is a ventilation system for the crankcase. This is to deal with blowby that is created while running.

Lastly, whenever I have removed the filler cap while running I've always had some amount of oil spray coming out and all over. Not a geyser mind you just enough to realize it's making a mess. Maybe that was just on the mills I've dealt with, maybe a BMW has better baffles.

In this case I don't think it will matter at all if you are just priming it, but that's my wild guess of the morning. Will be curious what the BMW mechanics have to say.



Originally Posted by Shannow
Missed the OP...but read the second...

The swept volume of an automotive cylinder is not a pure sinusoidal volume change.

For exactly the same reasons that you can't balance a 4 cylinder, there is a significant change in crankcase volume every 90 degrees, and a change in pressure...leave the oil cap off a running 4 cylinder and have a look...

And there's not enough to change any sort of priming mechanism post oil change.






Thanks for the replies. I deleted it because I figured it wasn't thread worthy and somewhat of a stupid question.

Shannow: Here is the SIB I had originally mentioned.

SIB


“It took untold generations to get you where you are. A little gratitude might be in order. If you’re going to insist on bending the world to your way, you better have your reasons.”

435i
Re: Oil flow and Vehicle start with oil cap off. [Re: Shannow] #5139004
06/20/19 07:19 AM
06/20/19 07:19 AM
Joined: Nov 2008
Posts: 13,993
NH
supton Offline
supton  Offline

Joined: Nov 2008
Posts: 13,993
NH
Originally Posted by Shannow
Missed the OP...but read the second...

The swept volume of an automotive cylinder is not a pure sinusoidal volume change.

For exactly the same reasons that you can't balance a 4 cylinder, there is a significant change in crankcase volume every 90 degrees, and a change in pressure...leave the oil cap off a running 4 cylinder and have a look...

I stand corrected then.

I have pulled the cap off my 4 bangers and figured that airflow was just air into the engine... hmm.


2011 Toyota Camry, base, 2.5L/6MT, 187k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 152k, ours
1999 Toyota Camry LE, 2.2L/4AT, 208k, his
Re: Oil flow and Vehicle start with oil cap off. [Re: BMWTurboDzl] #5139064
06/20/19 08:45 AM
06/20/19 08:45 AM
Joined: Apr 2018
Posts: 485
US
talest Offline
talest  Offline

Joined: Apr 2018
Posts: 485
US
You should feel air sucking IN and not pushing OUT is this correct

Re: Oil flow and Vehicle start with oil cap off. [Re: talest] #5139075
06/20/19 09:10 AM
06/20/19 09:10 AM
Joined: Dec 2005
Posts: 11,727
Upper Midwest
kschachn Offline
kschachn  Offline

Joined: Dec 2005
Posts: 11,727
Upper Midwest
Originally Posted by talest
You should feel air sucking IN and not pushing OUT is this correct

It can be both, the pistons displace air in the crankcase as well as the cylinder.


1994 BMW 530i, 242K
1996 Honda Accord, 277K
1999 Toyota Sienna, 418K
2000 Toyota ECHO, 281K
Re: Oil flow and Vehicle start with oil cap off. [Re: BMWTurboDzl] #5139811
06/21/19 03:27 AM
06/21/19 03:27 AM
Joined: Mar 2013
Posts: 873
UK
weasley Offline
weasley  Offline

Joined: Mar 2013
Posts: 873
UK
Don't forget the effect of blow-by, which positively pressurises the crankcase and is the reason a PCV is needed. If you run an engine with the cap off, the crankcase won't pressurise and you will get a flow of blow-by gases out of the oil filler.


2017 SEAT Leon 1.4 EcoTSI 150 FR Technology DSG
2018 Volvo XC60 D4
2011 KTM 990 SMT
Re: Oil flow and Vehicle start with oil cap off. [Re: BMWTurboDzl] #5139813
06/21/19 03:59 AM
06/21/19 03:59 AM
Joined: Mar 2015
Posts: 6,454
Virginia
bbhero Offline
bbhero  Offline

Joined: Mar 2015
Posts: 6,454
Virginia
I did this lovely little feat the other week by accident LOL


I was impressed how quiet my motor was running with the cap off.


Nissan Altima 3.5 Coupe
Carquest High mileage full synthetic 5w30
CQ blue 84356 Oil filter
"Treat your family like your friends and treat your friends like your family."
Re: Oil flow and Vehicle start with oil cap off. [Re: BMWTurboDzl] #5139815
06/21/19 04:04 AM
06/21/19 04:04 AM
Joined: Mar 2015
Posts: 6,454
Virginia
bbhero Offline
bbhero  Offline

Joined: Mar 2015
Posts: 6,454
Virginia
Not a stupid question at all...

There's zero doubt in my mind that you are very smart.

We all have areas where we don't know everything about everything... And asking questions is how we learn new things.


Nissan Altima 3.5 Coupe
Carquest High mileage full synthetic 5w30
CQ blue 84356 Oil filter
"Treat your family like your friends and treat your friends like your family."
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