Well, I finally put a gauge on the ragtop so I could see what the oil pressure actually was, before putting a new sender on it.
30psi cold, but warm...?
Higher is idling in Park, lower is idling in gear.
Crap.

As soon as I posted this, I remembered I was attaching files straight from my phone's 8MP camera. Sorry about that. Will fix later.

Sounds like mains are getting worn out. I hate it, I had a 360 do that. It was an unknown rebuild. Bore looked great, it was clean. I started it.and it was great...until it was warm.

I looked closer & saw the nylon tubing so that is a mech gauge. As you know it can't be driven with it that low. I would pull the dist & intergear & drill prime it & see what develops. Was the PSI OK before? any changes made that might be bringing this on? with the dist out you can see if the rear gallery plug is in place. holler back with any news

I had an old 318 in my 4x4 that was like that...Run a good thick oil (Brad Penn Straight 40 or 50) and it should be fine.
Back in September I put 1 qt. of cheap oil in the 383 in the Satellite and it lost about 8 lbs of oil pressure...

Before giving up on it try changing oil filter to some thing like WIX and a straight 30 weight oil.

I would start by pulling the pan and checking the oil pickup for debris blocking the pickup, like timing gear dross. 2¢

Robert

Is it making noise yet? I had an old beater that had the same oil pressure, thicker oil didn't help. As soon as you reved it up a little, the OP would jump to nearly a respectable level.

I beat the crap out of that car around town for nearly 2 years before it started making noise, shortly after the noise started, it began to overheat as well.

I just had to pull the pan off before I sent it away. The rod surfaces of the crank had groves nearly 1/8" deep on the top 1/2 of the crank, and the bottom of the crank journals looked great. Pull the rod caps, and the lower journals looked normal, you had to remove the caps an turn the crank 180 degrees to see the groves. One of the strangest things I ever saw. Gene

If it was a big block I'd say install a hi volume pump, but it's not.
If you don't want to drop the pan then try 20w50 oil, you might be just fine.

If it ain't broke don't fix it!

If it runs fine then keep driving it, IMO.

I had a 1981 international crane truck with a 304 V8 gas engine in it that I bought used for the crane on the back. It would show 0 oil pressure at idle warm and would go up to 25 or so when revved up. We used that truck like that for more than 15 years. I figured eventually I would have to overhaul the engine, never had to and then I sold it still running. That truck sat there and idled most of the time while the crane was being used. My

I ran 15W-40 diesel oil in it the whole time.

I agree if it goes up driving drive it.A new pump might increase pressure some.My old Ramcharger had the same thing.Bought it with like 160K on it and sold it with 280k.Still ran great and OP was almost always on 0 hot in gear.Driving it would go up.Guy that bought it was driving it 2 years at least after I sold it.Rocky

I had the same experience with a Chevy Lumina years ago. Warmed up and at idle it showed zero oil pressure and a red light would come on. As soon as the rpms went up it had pressure. The owner's manual said it was normal.

Everyone tells you it's OK. Maybe they're all right, maybe my experience was the exception. But I had something like that happen and it wasn't OK. The way the 318 oils is, the #1 main feeds the #1 rod journal, and the #1 main is the last in line for oil. I had replaced my old engine with a newer one with new bearings and rings. Because the oil pan was different I reused the old pan and pump. After a few thousand miles it started making noise driving around town and the oil light was on anytime the engine was at idle.

Disassembly showed the #1 main and the #1 rod journal with damage, everything else was fine. The main bearing was pretty much gone, but the main journal itself was OK. The rod bearing was down to the steel, the rod was blued and the rod journal was worn deeply, only on the half of the journal corresponding to the #1 rod. About 1/8" was worn off the underside of the throw. I had to replace the crank and one rod, plus all the bearings.

So I say get another 318 shortblock and swap it in. Or rebuild the one you have and put in a new pump and pickup tube. If you let it go long enough it'll get a lot worse.

R.

How much does the RPM drop when you put it in gear ?

Was the idiot light coming on when idling in gear and warm ?

What's your plans with the engine/car? Do you use it as a summer car only ?

The car has over 204,000 miles on it.

Oil pump was replaced in early 1997 and has about 25,000 miles on it. The guys who did it would have cleaned the pickup before buttoning it back up.

The idiot light would come on when idling in gear and warm after sustained highway driving. When I took it to Mason-Dixon for the Mopar Meet in May, it started coming on sooner (it would come on within a mile of my house, after being driven under 40mph) and staying on longer (sometimes even after putting it in Park). I haven't driven it farther than the local cruise night (2 miles from my house) since, because I'd rather not have the engine go when I'm 50 miles from home.

I don't know how much the RPM drops when it goes in gear (no tach).

People suggesting heavier oil: Do you really think I'm gonna pick up 15 psi just with thicker oil and a new filter?

It's a convertible with Dynomaxes, so it's hard to tell if there are new noises. The engine doesn't sound different when I'm just standing there with the hood open.

The car is a toy, but one that I usually drive about 1000 miles a year. This year, I basically lost the whole cruise/show season because of the oil light. Yep, no top-down cruising all summer.

I looked at small-blocks for sale in the classifieds yesterday, but the two that looked promising were too far away.

Oh, yeah, I didn't actually drive it anywhere yesterday, I just ran it in the driveway and tached it up a little to see if the pressure went up at higher revs.

Drop the pan and look at a few bearings ? If there is no metal to metal contact I would put new bearings in it and button it back up ... maybe get a set that are .001 oversize to tighten up the clearance?

Thicker oil is not the way to go about fixing it.

There is a lot of good advice here. I suggest you run the thicker oil (maybe even straight 40W or 50W)....while you're finding and/or building another small block. You can get a used 318 pretty cheap or find a 340/360 & build it a little if you have more cash. I would guess you'd gain about 10psi of oil pressure with 40W or 50W oil.

I have had three small blocks pull the same issue I will bet the pump took a dump period are the bearings worn sure but if I were you I would go to 20W 50 Oil or even straight 50 weight I fixed all my 318s with pumps or nothing at all and I just drove them If not racing forget it

Nothing is going to magically fix it short of hard parts replacements.

I suppose the bypass in the oil pump could be stick open causing this issue.

You could pull the pan and inspect the bypass as well as the bearings. that will tell you more than all our guesses combined.