View Single Post
  #4 (permalink)  
Old 11-22-2001, 11:07 AM
Lubrecon Lubrecon is offline
CC Member
Visit my Photo Gallery

 
Join Date: Oct 2001
Location: Houston,
Posts: 74
Send a message via AIM to Lubrecon
Not Ranked     
Lightbulb Oil Pressure

Pumps, oil pumps included, produce flow, not pressure. Pressure is the result of restrictions in the circuit or system. For instance, the oil pressure you see at start up is high, even at idle, and then decreases to some stable level, because of the oil's viscosity. It is cold, thicker, at start up, thus creates more resistance to flow than it does when the engine warms up, thinner viscosity. The oil pressure then varies with pump speed, oil flow, but should top oil at some rpm and not go any higher.

Bearing clearances, oil gallery dimensions, turns(90 or otherwise) all contribute to the restrictions in an engine that the oil sees. Viscosity is also a contributor as I mentioned. I am not an FE expert, but at some rpm, the pressure should not go any higher because the oil pump will bypass(relieve) over a pressure relief valve set at some predetermined pressure. Otherwise if the pressure continued to increase with rpm, something will have to give. Since oil is essentially incompressible, a positive displacement pump will continue to put out more flow with each higher rpm, and since you can only flow so much volume around the system, pressure will have to increase. At some point, a failure has to occur, pump, line rupture, or something.

High pressure at start up really means nothing. In fact it could mean that the oil is not flowing as it should. What you want is for the oil to flow as quickly as possible at start up so the main, cam, and rod bearings get oil quickly and don't rotate dry during the start up period. To do this, you need an oil with excellent flow properties at low temps. The best at this is Mobil 1, and in all high performance engines, I would use a 15W-50. It will flow quickly at start up and give you good protection at operating temp. It has a very high viscosity index naturally because it is a PAO, and that is why it will flow so quickly at start up.

Sorry for this to be so long. I am not questioning any one's experience with their set up.
Reply With Quote