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87 Appy, what is the oil pressure at idle and at running speed? I have a pressure gauge now. At start up 60 psi. When warmed up 6 psi at idle, 40 to 50 at 3000 rpm and up.
20-50 wt. oil. Any need to be concerned about 6 psi?

Thanks
 

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The oil pressure is always much higher when the oil is thick and cold. I wouldn't be worried about 6psi, 6psi is a lot if say you had a leak, the rate at which the oil would leak out at 6psi would frighten you!
 

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pisspodpete wrote:
87 Appy, what is the oil pressure at idle and at running speed? I have a pressure gauge now. At start up 60 psi. When warmed up 6 psi at idle, 40 to 50 at 3000 rpm and up.
20-50 wt. oil. Any need to be concerned about 6 psi?
pisspodpete, HOT engine oil pressure at idle is pretty unpredictable (that's why most oil pressure readings are taken at a higher rpm). Just a couple of RPM's difference in the engine idle speed can have a big effect on oil pressure. Even oil brand can effect hot oil pressure as not all 20w50 oils have the same base viscosity (some run to the high side on theviscosity index while others are much lower).

Another factor is theoil's hours of running in the engine. Oil tends to shear as it is run through the internal gears & bearings, the more it shears the lower it's base viscosity becomes. Here is where synthetic oil's shine as they have a much more stable base viscosity than most Dino oil's do.Engines with internal transmissions are the worst offenders hare as they tend to shear the oil the most because of the gear teeth.


The reason you have higher oil pressure when cold is the oil is MUCH thicker when cold. As it warmsit thins out & that is why the lower oil pressure when hot. Remember 20w50 is only 20 weight oil that doesn't thin any more than 40 weight would at somewhere around 100°c.

Here is an old racers rule or thumb. You need around 10 psi of oil pressure for each 1000 RPM of engine speed under load. That usually doesn't include low idle though.

Twisty
 

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in the past some manufactures would acyually point out that the oil pressure idiot light might come on at idol (BMW's especially). I am a fan of changing oil often and when on long trips I have been known to add stp along the way as I cannot do an oil change.
 

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Oil pressure will also drop when the engine is hot and idlingdue to increased clearances between the different types of metals inside the engine.

Aluminum expands at a far greater rate than steel does and when the aluminum expands it creates a gap where oil pressure can be lost. Idlingwill also create slow water pump speed and slow coolant circulation which in turn raises internal engine temperature which further thins the oil out even more.Idling is not good for any engine and if you can, try to avoid unnecessary idling as much as possible.

Keep the cooling system in good shape and keep the oil clean and fresh and youwill bejust finewith 40 to 50 PSI at 3000 RPM.

Vic
 
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