| Author |
Message |
Tom Bakowsky (Tbakowsky)
Member
Username: Tbakowsky
Post Number: 529
Registered: 9-2002
| | Posted on Saturday, August 16, 2003 - 5:13 pm: | |
ya what he said!! |
Dr. Erik Nielsen (Judge4re)
Junior Member
Username: Judge4re
Post Number: 164
Registered: 4-2003
| | Posted on Saturday, August 16, 2003 - 4:50 pm: | |
PV=nRT is for gases. You have to use an equation of state for liquids.
When the oil is cold, it is more viscous (i.e. more resistant to flow), meaning it takes more energy to move it around. As it heats up, the viscosity drops, and it is easier to move around. So when its cold, the oil pump has to work harder to get the same volumetric flow rate, hence the pressure is higher. Make sense?
Disclaimer: My Ph.D. is in chemical engineering, so I have a very hard time explaining it in English without equations... |
Tom Bakowsky (Tbakowsky)
Member
Username: Tbakowsky
Post Number: 528
Registered: 9-2002
| | Posted on Saturday, August 16, 2003 - 4:47 pm: | |
as the engine oil heats up it's viscosity goes down, so you see it as a drop in oil pressure on your gauge. If you take surup and heat it up on the stove it gets thinner right? Well the same thing happends with engine oil. |
Steven J. Solomon (Solly)
Member
Username: Solly
Post Number: 562
Registered: 6-2001
| | Posted on Saturday, August 16, 2003 - 4:40 pm: | |
This is for the engineers and physicists among us.
When I start my 360, engine is cold, oil is cold, and oil pressure gauge reads higher than normal, a few millimeters to the right of the "70" mark. As the engine oil temp increases, oil pressure drops (we are talking about driving at constant RPM's, so RPMs are not a factor). I remember my college physics class and the formula PV=nRT.PressurexVolume=n-molalityxR (a constant for any given material)xTemperature. This equation means that as temperature increases, pressure should also increase. They are directly proportional. Yet as the oil temp warms the pressure gauge reads lower and lower unless I really rev it to max. Why should this be?
Could the viscosity of the oil change so much from cold (fairly thick-low volume) to hot (very thin-high volume) that the increase in oil volume alone drives down the pressure? (remember that pressure and volume are inversely proportional).
What am I missing here?
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