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Originally Posted By: Shannow
Your oil pressure viscometer is measuring the viscosity of the oil as it enters the right angle turn into the bearing.
As I've done and reported the calculations a number of times before, at any reasonable RPM above a couple thousand and with regular bearing clearances the oil passing from the main bearing gallery into the UNLOADED side of the bearing is operating in the high shear range...
Therefore you are measuring viscosity...of the bulk oil, as it enters the unloaded portion of the bearing.
As I've repeatedly demonstrated, the oil temperatures in the LOADED part of the bearing can be 20+ degrees C hotter than the bulk (unloaded feed area). It often doesn't "feel" right to someone with no training, or experience in all facets of bearing lubrication, but the temperature rise IS there, whether posited against or not.
And oil pressure has no relationship to MOFT on the loaded side of the bearing, other than the viscosity of the oil as it enters the unloaded side.
Further, in addition to the oil pressure gauge not seeing what's happening on the loaded side of the bearing, it further, cannot "see" what's going on in the big end bearing. As you would understand the big end is (intermittently) fed already heated oil, suffers the greatest peak load (mains are an average load) and in addition the load is highly cyclic, which tends to pump oil out of the bearing.
Big ends are operating in a whole different world to what can be "seen" with bulk oil temperature and oil pressure.
Interesting.
Very interesting.
So bulk oil temps don't reflect actual oil temps in the bearing under load and can be much hotter at those spots,thinning the oil at the most critical area.
Very interesting indeed. Thanks Shannow.