I recently purchased a 1980 53 MY that was on the Arkansas river. I drove it from about 130 miles up the Arkansas river via the Mississippi to Chicago and north to Frankfort Michigan. A really long trip! I tell you this because many of my questions come from what occurred on that trip.First, on many occasions the indicated oil pressure on one engine would drop from 40lbs to about 10 lbs and slowly go back to 40lbs. I checked the reading at both stations and they both were the same or very close. I should mention that prior to the trip I had a new engine instruments and senders installed. This occurred on both engines.We were running the engines at 1300 turns to conserve fuel as there were no places to purchase fuel on the lower Mississippi until Memphis. And no others until Cape Gerardo Mo.(sp) The oil was checked every A.M. and filled to the line, and we ran from 6AM to 6PM.The boat is presently in heated storage in Michigan and any work could be done regarding this problem could be done.