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Old 25-Jan-2013, 18:10
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dunlop0_1 dunlop0_1 is offline
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Oil pressure question

Just been testing the 996's oil pressure. Now it meets the the recommended pressures both hot and cold, at idle and 4-5k.
However, there is no spec for what the pressure should be when the relief valve opens above 4-5k.
I would expect a drop but what to?
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Old 25-Jan-2013, 18:46
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Quote:
Originally Posted by dunlop0_1
Just been testing the 996's oil pressure. Now it meets the the recommended pressures both hot and cold, at idle and 4-5k.
However, there is no spec for what the pressure should be when the relief valve opens above 4-5k.
I would expect a drop but what to?

Relief valve surely is lifted by pressure and is not necessarily RPM dependent. Also viscosity will be a factor as will temperature. How hot is hot?

Also as the relief valve is opposed by spring pressure it will vary infinitely.
Just my thoughts probably bollox as usual.
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Old 25-Jan-2013, 21:01
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So if the pressure at hot idle is 15psi rising to 65psi max at 4-5k then when the relief valve opens creating a free flowing circuit as it where then pressure would drop back to somewhere around idle pressure? So you will only maintain the max pressure at the relief valve because after that the only resistance is from the oil galleries/crank etc. Then when the rpm decreases the valve shuts etc
Pressure is only created when resistance is met yada yada.

or is it my turn to talk bollox.

Last edited by dunlop0_1 : 25-Jan-2013 at 21:28.
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Old 25-Jan-2013, 22:14
batesy2 batesy2 is offline
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Right listen carefully,I will say this only once,(mock german accent)
The relief valve opens at a pre-set pressure dictated by the spring fitted,it will only open when that pressure is reached,
The moment the pressure reduces the valve will close but the drop only needs to be slight.
The valve will open and close rapidly but the pressure will remain at the max level at all times whilst the engine is at high revs.
Some engines never reach relief pressure due to wear in crank etc

Hope that makes sense

Batesy
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Old 25-Jan-2013, 22:21
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Quote:
Originally Posted by dunlop0_1
Pressure is only created when resistance is met.
Or is it my turn to talk bollox.

That is correct, spring pressure is constantly modulating the relief valve orifice, from a knats A**hole, to your not coming near me wi that.
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Old 26-Jan-2013, 08:20
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Quote:
Originally Posted by batesy2
Right listen carefully,I will say this only once,(mock german accent)
The relief valve opens at a pre-set pressure dictated by the spring fitted,it will only open when that pressure is reached,
The moment the pressure reduces the valve will close but the drop only needs to be slight.
The valve will open and close rapidly but the pressure will remain at the max level at all times whilst the engine is at high revs.
Some engines never reach relief pressure due to wear in crank etc

Hope that makes sense

Batesy

100% correct,and very well explained.
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