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#2479716 - 01/01/12 09:06 PM Oil Viscosity vs. Oil Pressure
blackdiamond Offline


Registered: 03/05/07
Posts: 630
Loc: Western Washington
What connection is there between oil viscosity and oil pressure? The engine in question is a 20r/22r hybrid that is driven like a race car. The owner indicated that 20w-50 wasn't cutting the mustard and the reason was that it wouldn't hold oil pressure at high rpm. At some point it seems that the oil pump wouldn't be able to keep up with the higher viscosity.

Any thoughts?
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#2479721 - 01/01/12 09:11 PM Re: Oil Viscosity vs. Oil Pressure [Re: blackdiamond]
GMorg Offline


Registered: 01/29/06
Posts: 2435
Loc: Mizzou-land
Exactly what does "hold oil pressure" mean in this context? Are you saying that oil pressure would not continue to rise or that oil pressure would actually drop at high RPM?

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#2479746 - 01/01/12 09:37 PM Re: Oil Viscosity vs. Oil Pressure [Re: blackdiamond]
AITG Offline


Registered: 12/22/06
Posts: 375
Loc: USA
On a theoretical level, pressure is the result of resistance to flow. Thinner fluids flow more easily, therefore less pressure is required to move them. Larger clearances result in less resistance, therefore less pressure will be required to move a given volume in a given time.

Practically, thicker fluids may result in more pressure but less flow. Worn components result in lower pressures but increased flow.

AFA the racer is concerned: I have no idea what he was getting at - sorry.

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#2479760 - 01/01/12 09:50 PM Re: Oil Viscosity vs. Oil Pressure [Re: blackdiamond]
sm00thpapa Offline


Registered: 07/09/11
Posts: 898
Loc: Spring Hill, FL
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#2479778 - 01/01/12 10:09 PM Re: Oil Viscosity vs. Oil Pressure [Re: sm00thpapa]
ltslimjim Offline


Registered: 08/06/10
Posts: 5505
Loc: WatUpDoc
Originally Posted By: sm00thpapa




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#2479963 - 01/02/12 07:08 AM Re: Oil Viscosity vs. Oil Pressure [Re: blackdiamond]
AEHaas Offline


Registered: 01/09/05
Posts: 1325
Loc: Sarasota, Florida
One reason may be that the oil pump bypass pressure is set too low for your application / oil grade combination.

The later chapters below may illustrate the issue:


http://ferrarichat.com/forum/faq.php?faq=new_faq_item#faq_haas_articles

Original (but edited by others) version:

http://www.bobistheoilguy.com/motor-oil-101/

aehaas
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#2480335 - 01/02/12 02:45 PM Re: Oil Viscosity vs. Oil Pressure [Re: blackdiamond]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
It could be too much heat, which can require a thicker oil to keep the pressure up.
But if an engine needs more than a 50 [which you have], it is extreme, for sure.

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#2480555 - 01/02/12 05:52 PM Re: Oil Viscosity vs. Oil Pressure [Re: blackdiamond]
aquariuscsm Offline


Registered: 12/30/06
Posts: 13903
Loc: South Texas,USA
If you need a thicker than 20W50,there`s always a mono grade 50 or 60.
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#2481135 - 01/03/12 10:04 AM Re: Oil Viscosity vs. Oil Pressure [Re: blackdiamond]
A_Harman Offline


Registered: 10/01/10
Posts: 6038
Loc: Michigan
Originally Posted By: blackdiamond
What connection is there between oil viscosity and oil pressure? The engine in question is a 20r/22r hybrid that is driven like a race car. The owner indicated that 20w-50 wasn't cutting the mustard and the reason was that it wouldn't hold oil pressure at high rpm. At some point it seems that the oil pump wouldn't be able to keep up with the higher viscosity.

Any thoughts?


Maybe the 20w50 is TOO thick. The higher viscosity oil will drain back to the pan more slowly than a 5w30, making it more likely that the pickup will starve for oil during hard acceleration or cornering. How much oil pressure is it maintaining at high rpm? Under what driving conditions is the oil pressure dropping?
_________________________
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2001 Dodge Ram 2500 diesel
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