Oil Pressure problem with 1991 5.0
I've searched through the subject and found much to read. But none quite like my situation. Was running about 55 or so when I noticed the oil gauge needle dropped to L. Went only a little ways to a station and checked the oil level. About half a quart low. So, started back up, pressure looked fine and moved on down the road. Mile or two later needle wobbles and goes to L again. I listened for engine noise and seemed to hear an increase in rattling/tapping. Pulled over again and stopped. Restarted the engine, pressure fine but when I revved up the engine the pressure would drop but return to normal at idle. Once again I took off and went short distance to find some oil. Topped off to full and made it home.
Based on my reading in this forum I bought a new sending unit and will put that in.
But I am thinking sludge here. Truck only has 63K miles on it and all of that is probably short trips (farm truck). Belonged to my father-in-law and I would not doubt he only used straight 30wt oil and only when he felt like it. Other than the sending unit replacement idea, what can I do to address my suspicion of sludge stopping up the engine drain holes and letting the pump starve? Any way to easily verify and de-sludge? Thanks.