I have a 1970 383 in my 74 charger and noticed the oil pressure fluctuating from 40 to nothing and back up to 40. I changed the oil and filter and it is now up to the 75psi it was when I first ran the motor this spring. Any suggestions as to what might have caused this?

 

possibly a bad oil filter ???

 

Exactly WHAT are you using for a filter?

(Hint: Fram does not make oil filters)

 

I am using a Napa gold filter..

 

Ok so I just took it out for a run and at cruising speeds I'm holding 45-50 steady. No jumping.. maybe it was the filter...

 

or the guage

 

After a fresh rebuild mine passed some metal. Bogged the motor some the same instant the pressure went down then back up. (Evidence was looking at the inside of the oil pump) . But it never went to zero.
New oil pump and no more problems so far. Not saying yours had this but pressure fluctuating reminded me of that.

 

Usually big fluctuations are uncommon but 383's have a slight hesitation in building oil pressure after sitting for a long time or after a complete oil change. Once you map the oiling system you'll see why. In your case I'd suspect something going on at the pickup or the tube but of course that depends on the weight of oil your using. Hard to pin down without a bit of disassembly but the pump is of the "positive" type so once it primes you should have oil everywhere, all the time. Check the bypass valve at the pump - you may have damaged the spring or it hung open. The variance in pressure may be just a one time occurance or the pump may be sucking air. Try a manual gauge in one of the two oil galley ports at the rear of the block and take it from there. I know of cases where the pickup tube cracked at the mounting flange and one where it actually fell down in the pan. I'm sure the problem will either go away or it will make it's presence known in the worst way. My oil pressure at idle is about 15 p.s.i. with a stock pump and using Wix filters and 50 p.s.i. at 1200 r.p.m. and above. Tops out at about 61 p.s.i. Speaking of filters, Fram and others are highly restrictive as they try to get down to the finest microns they can for filtration making them clog more easily. Next time you go to purchase a filter take a moment to feel the weight difference in different brands or just cut one open. Sooner or later you'll be using Wix.

 

it was using a wix