Hot Rods New (to me) SBC odd oil pressure problem

I'm an oddity as I don't have much experience with SBCs. But now I have one, a 350, stock and to the best of my knowledge is stock and never messed with, though it seems clean inside at 67,**X miles.
When I got it, it had 50-60 PSI hot at 2000, and I don't know, 20ish at idle. Cool! but one day, it suddenly dropped to just under 40 hot, 10ish at idle. Still OK, but a strange and instant drop, and no other issues. This one has an electronic pressure gauge, and since I had a new sender on the shelf, swapped it out with no change. Then, not being a smart feller, I bought a new gauge, and as expected, no change. I finally popped just a few pennies on a no-name mechanical gauge, and sure enough, no change. So I do indeed have a sudden reduction in oil pressure. Oh, and of course I first changed the oil (10w-30) and filter in vain. F it, I said, the pressure is OK, though the sudden drop is concerning.
Now, on occasion, on cold start, there is a light whirring like low trans fluid, but pressure around 20 PSI. In 15-20 seconds, the whir disappears, and the gauge jumps up to 45 PSI at maybe 1200 RPM (Cold, fast idle).
What might be going on?

 

Malfunctioning pressure regulator
Could be debris mucking things up

 

I'm thinking that most sources will tell you that Normal oil pressure for a 350 is 45 lbs. With around 20 or so at an idle.

 

Well……. The whirring noise, if it is coming from the engine, sounds like the pump cavitating. ****ing air. That causes the regulator valve to oscillate very fast and cause your noise. Although I have never heard it in an engine. Heard it many times in a transmission. I suppose an oil filter could possibly do that. If it’s not a good quality one. The low oil pressure, especially because it’s low at idle, tells me that the bearings are going away. That’s my opinion anyway. You could try maybe a straight 40 weight and see what happens.

 

Sounds like the pick up fell off the pump, add 2 qts of oil and see if the pressure increases.

 

it was pretty common for the pickup to fall off....way back when....

 

I’ll take any 10psi at idle SBCs you guys will give me.
The dummy light comes on around 7 ish. (I think)
The sudden drop and noise sounds concerning though.
I’m with the others
Possible oil filter/byp*** or pickup tube issue would be my first things to look at

 

OIL pump pickup screen partially plugged? Maybe the plastic coupler between the oil pump and the intermediate shaft broke and the pump isn't being driven smoothly. I've seen those break and the intermediate shaft disengage from the pump and no oil pressure.

 

Cheaper to pull apart now than after it kabooms.

Any metal in the filter ?
The weird noise could be cavitation and the pump making a weird noise .
Not over full i ***ume?

 

What seems logical (to me) is that the bearings must still be OK because the pressure does come up eventually. If it was a bad bearing thing, it would not increase because there would always be a gap for the oil to exit. So it sounds to me like you probably have a "supply" problem initially which could be the pickup or the relief valve sticking.

 

Yes, before I learned to tig them in place.

 

What brand filter ?
What weight oil ?

 

You mention not having any SBC experience so this might help you understand ... on a SBC the pickup tube is pressed/hammered into the pump. It is a friction fit and can fail. I have always understood that they (the pickup) can only be used once and must be pressed on perfectly the first time, you should not "swing it" to get better positioning of the pickup once it is seated. That being said, a pickup tube actually can simply fall out ... it is possible.

 

Most of us learned to tack weld them in place....

 

Or braze .

 

I like to JB Weld mine. Never had one fall off and no heat is added to the pump.

OP-sounds like the pan needs to come off or at least a borescope in the oil drain hole to look at the pickup tube. If I have the pan off, it's getting a new pump and pickup anyway.

 

I've had good luck by simply drilling a hole through the screen end then fabricating a strap that bolts to the screen ***embly on one end then I simply attach the other end of the strap to a nearby rod bolt

In all seriousness, the OP believes the engine is stock and not monkeyed with so that points toward the tube being pressed in from the factory, no glues, welds or brazing. With the OP being unfamiliar with SBC's, I thought him knowing how the tube is fastened from the factory (press-fit as opposed to bolt-on) would help him understand how it could fail. I also wanted to point out that IF the pump and tube have been messed with in the past, the "monkier" (he who monkied with) "could" have easily done things incorrectly (specifically rotating the tube in the pump after it is fully seated) which might/could cause the tube to fall out. Yes ... they can be welded/brazed/glued but the factory didn't do it that way and "Johnny's Pizza, Laundromat, Dating Service and Auto Repair" probably didn't as well

 

Thanks all, I'll start with adding an extra quart or so and see what happens. I don't have access to a garage right now (renting while I'm building) so I may just side-line the car until I have a garage again. I was wanting to pull the engine to re-seal it, and clean up the mess, and can look at it then.

 

Don't rely on the dipstick level being correct, start from an empty engine and fill with the recommended amount of oil (plus what an empty filter takes). I go with some previous ideas here, check your oil byp*** in the pump.

 

Man you're hard on Johnny !

 

If you can borrow a bore scope (or whatever those camera on a flex thing are called), you could drain the oil and stick the camera up into the pan through the drain hole. At least that'll let you know if the pickup tube is laying in the bottom of the pan.

 

My guess is that the pickup tube has rotated down and sitting on the bottom of the pan causing cavitation. For me that's the thing that lines up with all the symptoms .




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