rpm's up = oil pressure drop? ;-(

I'm still curious if you are putting any oil in the pan before fire up ? 68 degrees isn't the problem in my opinion -

 

no I never have put any oil in the pan., I would top off the dry sump tank with about 16 quarts, etc....
With the thinner oil I could physically watch the oil drop out of the dry sump at rpm's, with the thinner oil of course. At so many seconds into the fire up I could see oil returning from the evact side of the pump to the tank.
So I don't think adding any oil to the pan would make any difference once the engine has been idling for 45 seconds or so.-

 

Suction hoses can go flat, during high vacuum suction. Install an internal spring.

Earls makes a spring to go inside suction hoses.... It comes in -12 and -16 sizes.

I highly recommend spring use on all...fuel and oil suction hoses. They are really cheap insurance against suction hose collapse.

The fluid flow velocity at the wall of a tube is low, compared to the center, so the spring does not cause a problem in fluid flow.

From my past hose collapse experiences, this sounds like your problem to me. Your heating of lower viscosity oil reduced the resistance to pump oil in your system and allowed oil flow. The problem may return in the form of reduced oil flow, with use of higher viscosity oil at high rpm.

Problems like this cause me to use a "belt and suspender" approach to correction.

Ray H.