No oil pressure after oil change-oil pump?

Hi there,
i have a 1983 crusader 270 with approx 2600 hrs in a Tolly 26 that has been running like a champ. We just came back from a weeklong trip. I had noticed on startup the last couple days a bit of a whine that sounded like a pulley but went away quickly when started. Last weekend I changed the oil and filter. She started right up and ran fine as I warmed up before the oil change. After I changed the oil and filter I restarted. My alarm buzzer sounded and stayed on and I noticed my oil pressure gauge at zero and shut it down. I read a bit online and see that in some cases the oil pump loses its prime and to fill the oil filter when replacing it. I have never done this but gave it a try. Same result. Are these symptoms of an oil pump failing? Just seems odd that it’s at same time as oil change. I have been using 10w-30. Have dual helms and oil pressure same on both. Thx.

Try replacing your sending unit. If that doesn't work put a mechanical gauge on it and see what it is reading.

given 2600 hours, the engine is probably near the end of its service life...typically, dual helms still use a single sending unit (dual station type). Given that the gauge shows zero and the alarm is on, its very likely little oil pressure and I'd use a mechanical gauge to verify this...if the gauge shows ZERO with the engine running, the pumps not working.

I'd seriously consider replacing/rebuilding the engine given the accumulated run time.

Ok. So I went to the boat today. Added an extra quart of oil in the opposite side I filled from before. Put on an oil pressure gauge, from harbor frt. started up and lo and behold I’ve got pressure. 32lbs. Put back the Sending Unit and gauges read the same. So back in business for now. And yes I’ve been contemplating replacing rebuilding but hopefully now I can do it on my timeline.