I know you're all sitting on pins and needles. What will Steve find? How will this mystery end?

Well, the short story is, based on all evidence, that it was a clogged oil filter. So whichever of you it was that had the same experience (when you did an oil change and did NOT change your filter), you win your bet. As for the rest of you.. well, better luck next time.

Longer, more interesting story (for those of you that appreciate details)
Took the new over-the-counter oil pressure gauge and hit it with about 20PSI of compressed air. The gauge jumped to 20-25 pounds. I repeated the test twice with same results. So, I knew my over-the-counter gauge was good.
Hooked up the over-the-counter gauge to the copper line coming from the top rear of the block.
Installed a new AC Delco PF1218 filter. I of course pre-filled it although since I was going to use the oil priming tool, it probably wasn't super important to do that. Just an old habit.
Filled the car with 10W-30 conventional motor oil. I used conventional oil because I figured if this test didn't work and I was going to have to drain it all and tear everything down, I didn't want to be pissing away money on synthetic blend.
Pulled the distributor and inserted the oil priming tool (with a top collar and a mid-shaft guide, too -- although the mid-shaft aluminum guide didn't really fit snugly so there was still a little wobble which I muted by just holding the drill as steady as possible).
Hit the drill, about 1/5th speed. The over-the-counter gauge showed about 25PSI. This is promising!
Increased the speed of the drill to about half to maybe 2/3rds speed. The gauge now showed about 62PSI. I also saw some oil coming up and out above the rocker arms on both heads. Lacking a 3rd or 4th hand, I couldn't film this but I really wanted to. A bigger smile was crossing my face at this point.
Disconnected the over-the-counter gauge and reattached the copper line from the block to the black plastic line that runs to the oil pressure gauge in my console. With the help of my lovely assistant (my wife), she confirmed that when I spun up the drill to the same speeds I mentioned above, the gauge was showing the same pressures as the over-the-counter gauge.

Epilogue
I have NOT cut open the old filter (Purolator PL15313) yet but, since the ONLY things I effectively did were to change the oil and filter, I have to presume it was clogged. A clogged filter also tracks with the behavior I saw along the way here where the pressure being shown on the gauge just kept getting lower and lower and lower ... and lower. I will NEVER use that filter model again.

I've attached 2 pictures below -- one at idle and one at 2000RPMs. As you'll see, I'm reading ~70PSI at idle and higher than that at 2000RPMs. I know those sound high, based on other posts I've read along the way. But I don't think that I need to be concerned. FWIW, I'm sure that I need to check/tweak the timing as I'm pretty sure my distributor base plate didn't land 100% exactly as it was before doing all this work but I knew that the distributor rotor was pointing exactly where it was before I took out the distributor and I knew the advance canister was pointing almost exactly where I locked it down. In other words, I might be off 1-2 degrees at most from where I was so I knew I'd be safe to fire it up and see what everything showed.

In any case, I think I've saved an oil pan removal job and an oil pump replacement job.


Pressure at idle above (yes, the idle is a tad high since I haven't fine-tuned the timing yet, as I mentioned)


Pressure at 2000RPMs. Note that it's over 70PSI.

 

Well I'm quite OK with my guess being wrong! Happy you have solved the issue at minimal cost and PITA. And thank you for the ongoing thread - I have certainly learned a lot from your descriptions, and I'm sure others did as well.

 

That's great. Congrats on a successful resolution. And thanks for the update.
FWIW I wouldn't have bet ten cents on plugged oil filter,

 

Thanks for the update!

 

When you say conventional oil, you do mean something with Zinc, correct?

 

Do you know how much **** would have to be in an oil filter for it to plug?
Cut it open....dying to see it....

Jebby

 

Congratulations on a successful resolution. I've only ever used AC Delco sourced filters in my GM cars. There's a lesson in there somewhere.

Now that you have all the goodies, you need to compare how your OTC gauge compares to what's in your instrument panel. I would be a little concerned about the over 70 readings. Wouldn't be all that hard to insert a tee in the line to get them both together.

And whatever oil you uses, synthetic or "conventional" check on the zinc additive.

 

Let's hope it's not a bunch of metal shavings! Yes, absolutely worth knowing.

 

I had a fram filter fail.....those cheap ones are just a celluse **** membrane...ie cardboard. It could just be from dirt, crap and some shavings

 

Years ago - no, decades ago - there were some adapters or canisters or something which were supposed to allow you to use a roll of tickle tape as your filter. I was in the local Corvette Club at the time and a guy came to one of the meetings and made his pitch. I don't think he sold a single one.

 

Cool resolution..
if the filter clogged, wouldn’t the bypass allow pressure?

 

edit…holy cow! No bypass..looks like ac delco does..

 

Thanks for the feedback! I know that when I find an interesting thread and then it just peters out with no resolution, it makes me frustrated. If the loop can be closed, then let’s close it!

 

Ha! Probably not but I do know about the ZDDP additive (that’s the name, if I recall correctly. I used it in my ‘67 Mustang fastback years ago). I’ll look into getting some.

 

I’m going to be gone for 4 days but I’ll cut ‘er open when I get back. And maybe even share some photos — how EXCITING!!

While I don’t doubt you, Jebby, and I know you’ve got a ton of experience, I will challenge you to offer a different explanation. In the end, all I did was an oil and filter change (along with a lot of mini-checks along the way that just confirmed there weren’t any outside issues). I’ve detailed everything I did and tested. If all of that evidence I presented was presented to me, a clogged filter would be my first guess — regardless of whether I’d ever personally seen that or not. And, yes, if it is clogged with metal shavings, then the smile on my face will quickly fade.

 

I've been running AC Delco oil filters on my Vette for many years. I guess I always figured it's at least as good as OEM. Considering it is OEM. Never an issue, Thank God!
I run the PF454.
I buy em in bulk. As I live in Australia and you wouldn't believe what they get for a no name filter over here!
I can buy 6 AC Delco filters, delivered, for what the auto parts store here wants for one no name filter!

 

I would suggest taking a real close look at the oil bottle label. If it does not mention Zinc and you have a Flat Tappet Cam, then this whole thread is starting to come together about a plugged oil filter.

 

i will cut the filter open in a few days, as I said. And I will run a magnet through the oil I drained out. You may recall that I said that this engine was built by an engine shop when owned by a previous owner. Among the many build items, it definitely has a hydraulic roller cam in it (Xtreme Energy XR282HR). I’m presuming that it also has hydraulic lifters but the previous owner that had the build done did not confirm that (my fault for not asking). The shop that did the build lost all of their records when their water heater broke so short of tearing down the engine, I won’t know this. Based on my readings, it’d be silly to use solid lifters with a hydraulic roller cam and given that this work was done at a precision machine shop, I’m assuming they are hydraulic.

Other unknowns: Who knows how many miles the PO put on the engine after the build and whether or not he used any zinc additives or what oil brand he used.

In any case, I’ve already ordered the ZDDP additive and the car won’t be run until I can get that in … and until I’ve cut open the filter and dragged a magnet through the used oil for metal shavings. I will reiterate that the rockers were all snug (not sloppy) when I had the valve covers off the other day. If any cam lobes were wiped or even badly worn down, I should have found some sloppiness, right?

By the way, HeadsU.P., our primary residence is actually Indian River, MI. Depending on where you are in the UP, we may run into one another some time

 

Pump the brakes.

If you have hydraulic roller lifters (like a ZZ4, L98, or any modern engine), my understanding is that you do not need extra ZDDP. That's only for flat tappet cams.

 

If you have a roller cam the zinc won't hurt anything but is not mandatory.

Pat