Relation of oil pressure and temp

I agree with Mark. No

Peter Kl. wrote:

Maybe I am being misunderstood. No worries about sender, ground or type of oil.

If there is a strong relation of oil pressure to oil temp and shims are put underneath the mushrooms spring that will surely increase indicated oil pressure. Will I get higher or lower oil temps? 
With Bernoulli in mind the product of speed and pressure remains the the same, right? Thus, do I get reduced oil flow speed when pressure is shimed up. And if the flow of oil is slower due to increased oil pressure, will the flowing oil get better cooling cause it stays in the cooler a longer time?

Any experience with that?

As a simple farmer (retired) I will try to explain the relationship of oil to temperature & pressure (without reference to scientific luminaries or formulas).

Temperature

First think of the physical states that simple (single grade) oils can be in, from semi solids like wax/grease/fats to liquids as thin as Jet A/diesel (kerosene).

These physical states are governed by temperature  - waxes & greases will turn to liquid when subject to high temperature, Liquids like kerosene/diesel, will start to thicken/solidify at low temperatures.

Oils are sort of an in-between state,  but will respond in the same way to temperature - thinning (becoming more fluid) as they get hot, thickening as they get cold.

Thin & thick in oil terminology is called viscosity or weight,  which, if memory serves, is a measurement of how easily an oil pours at a standard temperature.

The whole thing then becomes complicated by modern engine oils containing additives (Multigrade oils) which change the the oils physical characteristics. Multi grade oils behave like thin oils when cold & thicker oils when hot.

In most engine applications, a thin oil is preferred at start up, for reduced cranking/starting effort and quick circulation (for protection) to the moving parts.  A thicker oil is desirable at operating temperature, to keep the moving parts apart (reduce wear). A chemical engineer would probably say its a bit more complicated but this will suffice, for the agricultural minded..

Pressure

Any flowing fluid, that is subject to a restriction will see a rise in pressure. Think of the oil system in your engine as a suction tube at one end (the inlet) with a pump 1/2 way, connected to a delivery tube. The delivery tube will dump its oil into a pan (sump). The open end of the inlet tube is immersed in the oil, in the pan to maintained the supply to the pump..

Engine oil pumps are usually, what is called positive displacement, that is they will deliver a set pressure at a constant RPM - slower & the pressure drops/faster & the pressure goes up. The viscosity of the oil will also influence the pressure - higher viscosity will see a pressure rise, lower will see a pressure drop. 

The (engine) pump starts and crates low pressure in the inlet tube causing oil to enter. The oil is squeezed by the pump and ejected, under pressure, into deliver tube. The pressure will remain constant as long as the pump RPM/temperature remains constant but this is not how a Rotax works. Rotax starts near idle 1700 rpm, at ambient temperature (say 20 C) and will take off /climb at around 5800 rpm at say 110C. So the pump must deliver sufficient pressure of oil over the full operating range. Too little pressure will result in to little oil lubricating all these moving parts (engine seized). To much pressure may cause a burst in the oil delivery system (catastrophic loss of oil).So the pressure must be controlled - this is done with a spring loaded valve. As the pressure rises the valve progressively opens, releasing over pressure - As the pressure drops the valve closes, maintaining pressure (oil delivery) to all those moving parts.

A warn pressure valve spring may release to much pressure, starving the moving parts of lubrication.

A warn valve "head" (not sealing) may bleed off oil at low pressure, also starving the moving parts of lubrication.

Increasing the valve spring tension by substituting a stronger spring or "shimming" may result in over pressure which may "blow" the system leading to oil loss - starving the moving parts of lubrication, oil onto hot components/fire or over windscreen/ loss of forward vision.

A warn engine may require increased relief valve spring tension and or a new oil pump, to maintain satisfactory oil pressures.

Caution should be applied to any non specified alterations to the relief valve settings.

Roger Lee wrote:

Oil pressure on startup tends to be a bit higher especially on cold mornings until it warms up a bit and then settles down to your normal running pressure. It can do this in many different types of engines. If your oil pressure is normal and then you advance the throttle and it drops to lets say 25 psi, but goes back up to 50 psi when you reduce the throttle it's most likely a poor ground. It the pressure drops way down or goes way up like 100 psi it's more likely the sender. There are a few other scenarios, but these seem to be the most common.

With a major caveat: a drop in oil pressure with increasing rpm is also a sign of a hose feeding the oil pump from the pump is sucking closed.

Also, shimming the oil pressure spring does not affect the normal running pressure at all, it sets the pressure (~75 psi) at which the bypass valve opens. There is seldom a good reason to change the factory setting.

More rpm gives more flow volume and pressure up until the bypass opens. If it opens before reaching full rpm, the engine is being starved of oil. So don't take off with cold oil!