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#3346414 - 04/18/14 10:51 AM Typical oil pressures in an engine?
HKPolice Online   content


Registered: 03/31/12
Posts: 205
Loc: Toronto, Canada
Seems like most filter bypass springs open up at around 12-18psi but when I google typical oil pressures, people are posting figures WAY above that. Apparently it's normal to idle around 10psi and for every 1000rpm it goes up another 10psi?

Wouldn't the filter be in bypass mode most of the time? I was under the assumption that filters don't bypass except for when the oil is really cold & thick and when near redline.

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#3346416 - 04/18/14 10:55 AM Re: Typical oil pressures in an engine? [Re: HKPolice]
bepperb Offline


Registered: 01/10/08
Posts: 4807
Loc: Milwaukee, WI
The filters open when there is a difference between the input and output sides. It doesn't matter what the total pressure is, only the difference.

So if an engine was driving down the highway with 50psi going into the filter and 48psi coming out and the bypass was 10psi it wouldn't be close to opening.
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#3346420 - 04/18/14 10:59 AM Re: Typical oil pressures in an engine? [Re: HKPolice]
dparm Offline


Registered: 04/19/10
Posts: 12555
Loc: Chicago, IL
10psi per 1000rpm is a ballpark, yes.
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#3346427 - 04/18/14 11:03 AM Re: Typical oil pressures in an engine? [Re: bepperb]
HKPolice Online   content


Registered: 03/31/12
Posts: 205
Loc: Toronto, Canada
Originally Posted By: bepperb
The filters open when there is a difference between the input and output sides. It doesn't matter what the total pressure is, only the difference.

So if an engine was driving down the highway with 50psi going into the filter and 48psi coming out and the bypass was 10psi it wouldn't be close to opening.


Oh ok I get it now. Are there any figures for typical pressure drops for oil filters? Any tests to see the amount of trapped contaminates needed to cause pressure drop?

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#3346466 - 04/18/14 11:33 AM Re: Typical oil pressures in an engine? [Re: HKPolice]
bepperb Offline


Registered: 01/10/08
Posts: 4807
Loc: Milwaukee, WI
You've come to the right place. This is old but a good place to start:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=314996

At one point someone had a similar setup in their car but I cant' find a link (I didn't look hard).
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#3346558 - 04/18/14 01:31 PM Re: Typical oil pressures in an engine? [Re: HKPolice]
ZeeOSix Offline


Registered: 07/22/10
Posts: 7578
Loc: PNW
Originally Posted By: HKPolice
Originally Posted By: bepperb
The filters open when there is a difference between the input and output sides. It doesn't matter what the total pressure is, only the difference.

So if an engine was driving down the highway with 50psi going into the filter and 48psi coming out and the bypass was 10psi it wouldn't be close to opening.


Oh ok I get it now. Are there any figures for typical pressure drops for oil filters? Any tests to see the amount of trapped contaminates needed to cause pressure drop?


Enjoy ... real test data from Purolator on a PureOne filter of average size (used on a 405 HP V8). As you can see, with hot oil a filter will flow lots of oil with not much pressure drop across the filter.

http://www.bobistheoilguy.com/forums/ubb...451#Post1619451

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#3346563 - 04/18/14 01:32 PM Re: Typical oil pressures in an engine? [Re: HKPolice]
Realtech214 Offline


Registered: 02/01/13
Posts: 631
Loc: Florida
My silverado has 40psi at idle (700rpm) and about 50 in the morning at idle. With 5w30
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#3346573 - 04/18/14 01:45 PM Re: Typical oil pressures in an engine? [Re: HKPolice]
Zaedock Offline


Registered: 09/10/05
Posts: 3843
Loc: Massachusetts
As mentioned, oil filters bypass with differential pressure.

This can occur when the engine is cold and the oil is viscous and it can also occur for a moment at operating temp when you go wide open throttle.
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#3346764 - 04/18/14 05:47 PM Re: Typical oil pressures in an engine? [Re: HKPolice]
RF Overlord Offline


Registered: 11/08/03
Posts: 3172
Loc: Cape Cod, MA
Ford modular (4.6L etc) can have 100 lbs pressure at cold startup, but settle down to 25 at hot idle. I believe this is one of the reasons Ford insisted on putting fake gauge in their cars.
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