I had the same oil pressure problem. Weld on the oil pick up cracked and the pick up fell off. At this point you are sucking oil from the highest level and getting air as RPMs go up

I'd try 7 qts and 10-40.. also... check your electrical connections to the gauge.. also make sure you have a good ground for the gauge and the engine block. If that doesn't fix the problem.... I'd take the engine out and remove the pan... see what is going on.. Maybe the pick-up has broken off...

That is exactly how my gages behaved when I purchased my boat. I experimented with lowering the oil level until this aereation would stop and oil pressure would hold at 5000rpm. There was a oil level that if I exceeded by even a 1/4 qt., it would start dropping pressure again at elevated rpm. When I pulled the engines I found no windage trays. Different problem for you, but same symptom. Like Reed said above, try lowering the number of qaurts. I just kept sucking a lttle more out with the vacuum pump and running it until the pressure wouldn't drop any more. Then I knew the proper level. Don't run the engines any more than absolutely necessary with dropped pressure, the engine is being starved for oil. Main bearings will not last.

Good luck

BT :cool: