Intermittent Oil Pressure

my68barracuda said
If you are not reading off a known good mechanical gauge do that first.
If you still have a low oil pressure issue after verifying that with a second gauge I would suspect that the oil by pass in the oil pump is sticking open. The bypass is intended to bleed off oil directly back into the oil pan at high oil pressures. If the piston sticks open it will bleed off oil at low oil pressure.
You will need to remove the oil pump to service it, but that is not too bad with the slant’s external pump.

Mechanical gauge, pressure switch, and engine knocking all agree!

Murray said
Does it have new main and cam bearings? And it has a new oil pump?

Yes, yes and yes! This is where it gets a bit weird. Cam is from a 68, and has the wider oil lands and block has narrower 75(?) and up bearings. I couldn't see that this would create a problem. Maybe someone else has some thoughts on this.

dirty white boy said
oil pump drive stripped and slipping

Just finished removing motor to replaced pump. Camshaft gear looked fine.

RustyRatRod said
He said he put a new oil pump in it.

Things I would do. Like John said in post 2. Put a GOOD mechanical gauge on it. If you see the pressure loss THERE, get her back out again.

I would from there, inspect the camshaft gear VERY closely. They have been known to fail. Look at the oil pump gear too. There was a rash of oil pump gear failures with the slant six for a time. If both those look good, "MY" thought is, there is a blockage in the system somewhere....probably some sludgy crap hung up in an oil galley. Unscrew the oil pickup. Inspect it very closely. Sometimes they can get sludge buildup under the shield and you cannot see it. Make sure the tube is unobstructed. Also make sure the passage in the block to the pump is clean and clear.

I would remove the oil galley plug directly behind the cam gear and apply shop air pressure to see if something gets dislodged. This if course with the oil pan off and the oil pump removed. I say go in at the oil galley behind the cam gear because this will be applying pressure backwards and is more likely to dislodge "something" if anything is there. You'll also not want to be standing in the area where the oil pump mounts, rather, I would hold a gloved hand holding a shop rag over that area to see if you catch something on the way out.

Next, I would remove the rocker shaft and rockers. Find the oil feed hole in the head. On the slant six, the hole for the oil feed is in the very last rocker shaft pedestal, that would be closest to the firewall. Apply shop pressure there. As mentioned, this will be applying pressure backwards through the system and possibly dislodge any obstructions.

Beyond that, You can also run engine cleaning brushes through the oil galleys. "I" would much rather do that with the engine torn completely down at that point though, so I could rewash the block as if it has just come from the machine shop.

The father down you go and more you do, you'll find "whatever" it is eventually.

Now, before you go runnin back out to yank it back out.......you HAVE tried another filter, right?

Man, I was really hoping for some advice that doesn't require yanking the motor again! :D I'm planning on moving, and I was trying to put a project back together, not take it all apart again.

I did check when I had the pan off, and the pump inlet was clear. Also replaced the pickup tube, which I was shocked I could get new. So pump inlet is clear. I never checked the output for plugs. My thought was having a plugged oil gallery would cause high oil pressure as the oil would just go over the relief all the time.

I never took off the cam gear cover. Makes me wonder if the plug has come loose or something. Either way, if I can pressurize with shop air, maybe I can find the leak. I should also check that I didn't put together something wrong in the rocker assembly.