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Discussion Starter #1
its the time of year i do all the maintanance stuff on the car. one is changing oil. last year i ran a 10-40. just thinking maybe go 10-30 instead. so the question is, will changing oil weight by 10 will that change oil pressure or it will stay the same.
 

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I think that people tend to go to heavier weights when their oil pressure is low or the engine has lots of miles on it.

You might see a small reduction but I don't think it will be significant.

Was 10-40 was doing what you wanted it to do?
 

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Discussion Starter #3
10-40 was doing good. might have gone thru 3/4 of a quart for 1500 miles last year. at first start up oil pressure is 38 psi an when warmed up at around 30-34 psi, an in gear idle warmed its down to like 20 psi. am i'm thinking about 15,000-20,000 miles on engine 327 ci.
 

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Is there something you are after? I would keep running the same oil and go.
 

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Discussion Starter #5
i guess i was more interested if oil weight has anything to do with oil pressure.
 

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i guess i was more interested if oil weight has anything to do with oil pressure.
It does to a point. Oil pressure is a function of the resistance to pumping of the oil. So given a specific viscosity oil, it has to pump through the clearances of the engine. The tighter the clearances, the more pressure. And on the flip side, the higher the viscosity to get through those clearances the more resistance, the higher the oil pressure. However, the oil pump will have a bypass valve that will open at the same pressure regardless. So you can have higher pressure at idle with heavy oil and at higher pressure the bypass opens. With thinner oil, it will take more rpm to reach the same pressure because of the positive displacement oil pump, but once it gets there, the bypass will still open.
 

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Discussion Starter #7
bracketchev thanks. so the pressure is affected by a few things, clearances, viscosity, an rpm's. so thinking that i'll stay with the 10-40 with 8 oz. of lucas zinc additive.
 

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Discussion Starter #9
10- 40 mineral ? not sure what you mean its STP pro formula 10-40 conventional oil. i liked the valvoline 10-40 but they don't make that any longer.
 

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Oil is also a coolant so oil pressure isn't the only thing to consider.You want the oil going through fast enough so it doesn't get too hot.I run 20-50 but my bearing clearances are on the loose side.Heavier oil also puts more load on cam and distributor gears as well as the pump drive.Short,sweet article here cuts to the chase on the science.
http://www.superchevy.com/how-to/engines-drivetrain/4380-bearing-clearance-info/
 

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Discussion Starter #11
that was a good read. sure is a science to oil flow.
 

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Discussion Starter #13
some one else will have to answer up on the use of synthetic oils in a 50 year old engine.
 

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If it ain't broke don't fix it.


Didn't you just DO that ........................ lol

and , Have a Happy New Year, buddy .. :yes:
 
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