So a few months back I changed the oil and filter on my L185. Within minutes of working the tractor bush hogging the oil light comes on. I was right by my shop and immediately pulled in and killed the engine. I posted on here about it and took the advice from several people. I replaced the oil sending unit, installed a manual/visual oil gauge, and changed the oil and filter again. After cranking it then I have great oil pressure. Cold idle is 60 lbs and after engine gets hot still has 27-30 lbs. Now my issue is after working the tractor for a while the oil light will come on and the visual pressure gauge will be bouncing every couple of seconds. The light will stay on but the gauge bouncing around will be swinging 20lbs both ways. What could this be?