Warm oil pressure higher at idle?

I know there are numerous posts about oil pressure, but I have been unable to locate an answer to my question. My oil pressure seemed a little low at cruse (55PSI) on my overhauled O-360 so I added a few washers. While looking over my EFIS engine data after the washers, I noticed my oil pressure (after it is warmed up to 180 degrees) actually increases from 85psi to 89psi when I pull back to idle for landing. Is this normal? Is 85 too high for normal cruse? I get a reading of 100 psi and a high pressure warning at start up when the oil is cold but that usually settles down once the oil hits around 100 degrees. As always I appreciate any input.

GEM

I forget the lycoming specs, but thought the range was up to 100 PSI, but it may have been 90. You need to look at a manual. It will tell you the range and will likely identify whether that is a Warm oil number or a Max number.

On the idle pressure, does it stay at 89 or just go there briefly before falling? I don't think I would worry about the former, but idle oil pressure should be quite a bit lower than at 2400 RPM. If this is not the case, I would be doing some research, though it is "in spec." Lycoming only lists a low end for idle OP, I believe, and I am pretty sure it is 25 PSI. I can't remember an engine that had an idle OP the same as at speed. However, I am new to aviation engines.

Larry

EDIT: My O-320 manual lists a warm range of 60-90 and a start up maximum of 100 PSI. It lists idle pressure of 25 PSI. You'll need to check the appropriate manual for your engine

Oil Pressure

Max for cold start was changed to 115 # quite a while ago. Top of the green is fine for cruise. There are many who believe as I do that high green oil pressure will extend the life of the valve train on a Lycoming.
Idle pressure on the ground and flight idle in the air are two very different scenarios. My understanding of the minimum 25 # idle is that this is for ground operations only with the idle r/m set to Lycoming specs.

Dropping throttle, but relatively the same RPM, that yields significantly higher oil pressure is troubling. On the surface of this, under load the crankshaft orbits in the bearings, that orbit will allow more oil to flow than idle at the same RPM. As throttle is dropped the crank main bearing loads are lessened and the crank will be more centered. If there is 10-15-20 psi increase, (at same RPM) that should trigger some further inspection. I would immediately check crankshaft end play and take the oil filter off -check for metal, then remove the suction screen and also check it for metal. Maybe - oil filter, screen, then crank in rank of easiest to do.

edit: if only 85 to 89 PSI that is not significant, and not an abnormal reaction.