ive seen all the messages in this forum talking about 351m's and their oiling problem. im having the same problem. a few months ago, i installed a edelbrock intake and carb on my motor. before and after the installation the oil pressure was fine (aprox 40 lbs.) about 2 days later, i was riding around and noticed my stock oil pressure gauge almost as low as it would go, but the lifters weren't ticking and the motor sounded exactly like it did before. i replaced the gauge and i also replaced the oil pump. now with the truck idling hot, the oil pressure ranges from 5lbs to 0 lbs. at 2500 its about 15 lbs. have any ideas why it lost pressure so suddenly?

 

Stock gauges aren't all that accurate, espically after they get old. Could be that you had the problelm for a long time but until you started disturbing the sending unit it was reading incorrectly. If you have any kind of mileage on the 351m (even 70k) your main bearings are getting thin... Thus low oil pressure. Time to install some new ones

 

I would replace the sender unit or install an aftermarket gauge before I got too excited.

 

This sounds almost too simple, but first check the wire connection to the sender unit. Make sure it's tight. I've had loose connections to give erratic pressure readings.......

 

I guess i should have made it more clear... when i replaced the guage, I meant I installed an aftermarket mechanical gauge. I was kind of figuring probably mains or cam bearings. oh well, more money

 

nasty77f150

Your bearing problem will be in the bottom end.

 

Pull your engine down and plasitgage the main and rod bearings. I never assemble an engine without performing this check.

Also check your oil galleries that extend from the pump. There is a restricted passage right at the pump mounting surface that needs to be drilled out. There may be other restrictions in the passages that will need to be cleaned out, modified, or re-drilled. Only a complete inspection will determine where a problem may be. I have a feeling that the main passages out of the pump may be the root cause of the notorius low oil pressure problems in these engines. It may explain why some engines suffer this malady and others don't, -just small manufacturing differences.

 

ill try your suggestions and let yall knpw what i come across.