IML: Re : pressure vs volume

["mike and linda sutton" <mikanlin62@xxxxxxxxxxx>]

This comes up all the time in various forms. Follow along....your oil pump 
is a positive displacement pump meaning it can move a set amount of oil each 
time it rotates, whether it is a spur gear style or a rotor style like 
Chrysler uses.  So for EXAMPLE, if it can displace an ounce of oil for each 
revolution of the pump it will move 1000 ounces at 1000 engine rpm. Now, if 
the various clearances in the engine bearings, crankshaft, connecting rods, 
lifters, pushrods, let less oil past them than the pump can move you will 
get pressure.
If this doesnt seem clear, remember that we are talking FLOW here, and 
resistance to FLOW causes PRESSURE. Dont think so..go turn on the garden 
hose and let it run, youll see flow. Then put your finger over the end of 
the hose and close it off about half way, you reduce the flow but increase 
the pressure.  Its not quite the same as the kind of flow vs pressure you 
see in hydraulics where there isnt any leakage desired because in an engine 
its a given that you will have oil leaking past the various clearances in 
the engine, thats how it is designed. The oil cools as well as lubricates.
This is also why as an engine wears out the pressure will drop, because the 
clearances get larger as the bearings and other surfaces wear. Since the 
pump can still only move a set amount of oil, whatever that amount is, the 
resistance to the flow of the oil lessens and the pressure drops 
accordingly.
Use a high volume pump as opposed to a high pressure pump. The only 
difference between standard and high pressure is the relief spring and you 
dont need higher pressure anyway. A high volume pump will give you more than 
enough oil flow to create  good oil pressure.
Mikey
62 Crown Coupe 


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