Low oild pressure on new engine revisited... and resolved

[mckpaul]

Made a post a while back about low oil pressure readings on a freshly rebuilt 305. I bought a cheap Sun Pro mechanical gauge from the auto parts store a while back, just got around to hooking it up this weekend. I didn't hook it up where the sending unit is for the gauge since it's a tight fit there, but I removed the oil pressure switch near the oil filter that provides voltage to the choke circuit. I shorted those wires out with a jumper so the choke would work and connected the little plastic tube for the mechanical gauge where the switch was, which allowed me to watch the mechanical gauge and the stock dash gauge at the same time.

The mechanical gauge showed almost 60 lbs on the cold running engine while the stock gauge showed somewhere between 15 an 30. After warm up, the mechanical gauge showed about 25 lbs at idle, and went up to about 50 when revved, more along the lines of what I expected, and the stock gauge just stayed around 15.

I noticed oil working it's way up the plastic tube toward the gauge, so I loosened the connector at the gauge while the engine idled and bled the air out making sure I had oil right up to the gauge, but it didn't change the readings, so I feel much better about my oil pressure. Got a couple of stock oil pressure gauges coming from a couple of board members to try in the dash. I've already changed the sending unit so hopefully a different gauge will read correctly. If not, I guess it's possible the oil passageway in the engine to the sending unit didn't get cleaned out correctly of something so I may have to deal with that, but at least I know I do have enough pressure now. Thanks for all the responses in the old thread giving me suggestions.