Pulling my (remaining) hair out trying to resolve a random low oil pressure issue.

In the summer of 2012 I noticed on one my Gen VI motors, which has always had solid oil pressure in the past, started up with 0 psi on the gauge. Before I could reach for the key and shut the engine off, the gauge quickly popped up to a happy 60 psi and stayed there. No biggie... must have been a stuck sending unit or gauge. I didn't think anything of it and proceeded out onto the lake.

Well, in a combination of a perfect mechanical storm, the OTHER engine popped a water line off the sea pump rapidly flooding the bilge. I caught the water line problem in time and shut off the engine. As I was idling back to the ramp on the other engine, I noticed that the oil pressure gauge had again dropped to 0 psi. I tapped the gauge a couple of times, but it never came back up. If I revved it up to > 2000 rpm, the oil pressure would pop back up to 60 psi, but then immediately drop back to zero at idle. Additionally, I could hear the valvetrain starting drying out so I didn't want to put any more stress on the motor than necessary.

I unfortunately had no other choice than to idle back to the ramp on the one working engine with zero oil pressure. After pulling the engine out, I confirmed that the main bearings were toasted. A local machine shop turned the crank and new main / rod bearings were installed over the winter.

After a long spring a a bunch of trips to Korea (Enjoying your cell phone battery? You're welcome!) I finally got the chance to reassemble the motor and drop it back in the boat. Before I dropped in the distributor, I used the priming shaft and was able to make 40 - 50 psi with an electric drill. It was REALLY working the drill, so it was definitely making good pressure. After dropping the distributor back in and firing it up, it was AGAIN making ZERO oil pressure at idle.

What
The
F#%k!?

The heads and deck have been milled, so I though that the distributor height might have been too high but a quick grease check showed a good 0.350" engagement of the oil drive shaft into the distributor gear / boss.

What am missing here? It seems that I'm chasing the same problem that haunted me last year. Is there a relief valve that could be dumping ALL oil pressure at idle but then suddenly "pop" open at higher rpms?

Any advice is appreciated. Thanks.

-Bayley

When you run metal through the engine It is necessary to replace the oil pump, cooler and oil lines due to metal contamination/damage that is impossible to clean. Did you replace these items? If not, you may have a do over on your hands.

oil lines reversed on remote filter?

Oil cooler was flushed clean and new pump was installed.

Chevy builds oil pressure in the bottom end. What kind of clearance do you have on the crank? Did you replace the cam bearings? We need as much info as you can provide.

I would switch to good sender and gauge. Do a short test run. If problem stays the same I would say you probably have a bearing pushed out a little...

Is the distributor installed at right height? that can let oil pressure bleed off, what kind of coolers you have? not all can be flushed.....

Use mechanical gauge to check pressure until you find the problem....

even on a drill you should have more then 4-50 psi mine pump 78 on both engines off drill, I would assume all block plugs are in, or you would have not gotten any on drill either, did you watch oil come out of rocker tips?

I doubt you have ZERO oil pressure, please use mech. gauge.... and double check oil lines off cooler, you can reverse them and waste engine....

I've tried multiple senders and they all give me the same results. It's also pretty obvious at idle that I'm getting no oil pressure. The valve train goes dry and the rods will start banging if I let if go hard enough. However, when I spin the pump up with the priming rod it'll build good pressure.

relief valve in pump most likely hanging up...change the pump...

I tried that. Replaced the pump, same issue. How common of a failure is this?