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I've got a '73 Stingray with a built 350 SB in it. Previous owner(s) were the ones that did all the rebuild work. Anyway, that's beside the point. From Day 1 of my ownership (November of 2021), I have always noticed my oil pressure gauge (stock mechanical gauge) reads low (maybe 20psi) and never really wavered much from there. It *might* occasionally get to 30psi but I couldn't testify to that on the stand in a court of law. To be honest, I never cared much what it was reading because the engine is a strong runner and has never given me a reason to think that something might be up. I just always figured that the gauge was "tired" or something.
I should say that this car is only driven sporadically and, even then, only for 6 months out of the year (from November through mid-May, normally). Beginning November of '23 (after sitting from May of '23 to November of '23), I noticed that the oil pressure gauge was reading really low... as in it was barely registering at all. In fact, the last time I had the car out, it was reading a flat zero. I continued to chalk this up to a potentially "tired" gauge. I don't know if I'm being paranoid or not but I kind of feel like a hear a noise of a ticking lifter... but that could just be paranoia.
In the interest of getting some more data, I decided to borrow a fuel pressure gauge (I know it's not fuel but oil is still a liquid, right?) from O'Reilly's Auto. I made up some brass adapter fittings from Ace Hardware in order to allow me to connect the standard fitting on the gauge to the 1/8" copper line coming from the intake manifold and then I fired up the engine. Much to my chagrin, the loaner gauge also showed zero. *GULP* So much for my guess that the Corvette gauge was "tired". After disconnecting the pressure gauge, I also noticed absolutely ZERO oil in any of the fittings. Nothing.
So, I'm thinking one of multiple things could be occurring. Maybe...
the port on top of the intake manifold -- the port where the small 1/8" copper tube comes out which runs to the gauge -- is clogged OR
maybe my oil pump has given up the ghost OR
maybe there's a bunch of small crap in my oil and one or more oil galleys are constricted OR
something else I haven't even thought of (but perhaps one or more of you has some insight on)
The oil and filter have less than 1500 miles on them. The filter is a Purolator PL15313 and the oil is a synthetic blend Valvoline 10W-30. Based on what I've read on this forum, a bad oil pump is actually an unlikely cause. Also, if the oil pump truly was shot, I'd be hearing a lot more gut-wrenching clatter than I am and/or I would already have destroyed the engine.
Since I don't see any oil actually coming through the 1/8" copper line from the top of the manifold, I don't think that buying a cheap mechanical oil gauge from O'Reilly's as an additional test is going to give me any other reading than zero, either.
I will tell you that I do not own a cherry picker and would prefer to NOT blow the engine, thereby requiring me to have to pull the engine and trans. In fact, I think I'd sooner sell the car right now than have to go down that road.
In closing, my question to you all is this: "What would you suggest that I do to truly find the root cause of what's going on?"
Last edited by sschultz2929; Feb 19, 2024 at 04:41 PM.
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)
uh,
easy to pull pan and look.
pumps have quit
drive rod on distributor have failed
pickup snorkle have dropped off
don't run it.
pull dist and check pump shaft
spin oil pump and look for oil at 1/8 hose or valve rocker
You SHOULD be concerned. I would get a known good mechanical gauge and hook it up to the correct port. (See post #2 above.) Then get an oil pump priming tool, remove the distributor, install the tool and spin it up with a drill. If you still dont get pressure, you are going to have to drop the pan and see what's up with the pump and pickup.
One more thing: "oil is a synthetic blend Valvoline 10W-30. "
Make sure your oil has adequate zinc additive, i.e. ZDDP. This wouldn't have anything to do with your oil pressure, but down the road, lack of this could have serious consequences as I found out using synthetic Mobil One.
Good possibility the oil pump pick up screen is loose, plugged, or at the incorrect angle or even too far off the bottom of the pan.
It's time to drop the pan and not only check the pick screen, but I would also plastic gauge one or two rod bearing and one main bearing for reference.
It may be time for a new pump and maybe a new rear-main-seal if dripping.
In most cases the exhaust & starter can remain. Two nuts on the idler arm bracket, and the whole linkage drops away.
An extra-long 3/8 drive extension removes the pan bolts.
It's not a horrible job. The worst part is scraping the old pan gasket off.
On my '71 SB, the oil pressure line is plastic and you said yours is copper so I asume the PO changed that during the rebuild. Since you tried a fuel pressure gauge with a zero result, my next step would be to isolate the line (copper or otherwise) from the engine to the gage and see if that's clogged. Test it to see if oil comes out the gauge end while turning the engine or remove it completely and blow air through it. If that's OK, I'd get an actual OIL pressure gauge from the parts store (even just a cheap one) and test it with that instead of a fuel gauge. Yeah, liquid pressure is "just" pressure, but viscosity differences MIGHT enter into the picture and I'm no expert so it's a FWIW suggestion. If no change, then the suggestions posted by others would be in your future,,,
Start with the easiest, and cheapest troubleshooting techniques first.
This will sound crazy, but try changing the oil filter. Many years ago, my oil pressure dropped to zero, and I had the car towed home....dropped the pan, changed the pump, new oil, and same problem.....yes, I did not change to filter. When I changed to filter, everything was fine, and back up to approx 40psi. Stupid me but never heard of a filter failing like this before.
Once you do that, do not run the engine, but rather prime the motor with a priming tool, and check to see oil make it way to the rockers.
Is the distributor stock or aftermarket? Some aftermarket distributors have an adjustable collar(not part of the hold-down clamp), where is seats against the intake manifold. It is possible that the collar has shifted, and the distributor has raised enough to no longer engage the pump shaft.
After checking these items, If you do have the oil pressure guage at the correct port, and still no pressure registering, time to drop the pan.
My strong recommendation is that whenever you are going through these troubleshooting steps, always do your testing by using a priming tool and drill (especially if you drop the pan and change the pump). If the motor has been run with zero pressure, you don't want to do any(more) damage, if you can avoid it.
Thanks for the suggestions, guys. It was on my laundry list to replace the oil pan gasket anyway so I guess I’ll be dropping the pan. I’ve read posts about removing the 2 bolts that hold the idler arm in place and that will allow the steering linkage to be pulled down enough to drop the pan.
Regarding the oil pressure gauge line, it’s copper coming out of the block but transitions to a black plastic line that runs through the firewall to the back of the gauge. And there’s no oil coming through it to the transition point (a simple 1/8” union) so there’s really no point worrying about the rest of the line.
Given that the pressure readings started to drop slowly over time and didn’t simply go from XXX to zero, the “blocked/clogged oil filter” scenario actually sounds like it might have some merit. BUT, I’m going to drop the pan anyway — and of course a complete oil and filter change will also be done. Don’t most oil filters have a bypass so that if the element gets clogged too badly, oil will still flow?
For the pan, I’ve read about there being 2 different 1-piece gaskets, one thinner than the other. I believe I’ve got the 09T (thinner) version, based on model year.
As for an oil pump spinner/primer, this is something I’ve never used but that I have heard/read about before that fits into a drill, right? Something that could be borrowed from O’Reilly’s or AutoZone?
Last edited by sschultz2929; Feb 19, 2024 at 06:12 PM.
If you do want to test the oil pump, the primer tool will require a hefty electric drill to spin it at any reasonable RPMs. This priming is not a job for the little 3/8 household battery drill. A corded 1/2 drill with gobs of torque will fit the bill.
The priming tool can be had at Summit. Moroso and others make them. Around $25.
I recommend one with a collar that stabilizes the shaft into the Intake manifold hole.
Another possibility is the pressure spring inside the pump itself. Rare, but it may be weak & shot. Those springs come in color codes to achieve the oil pressure
you desire.
And I would question the health of the oil filter by-pass adaptor plate. There is a spring-loaded valve on there that could be wonky.
.......As for an oil pump spinner, this is something I’ve never used but that I have heard/read about before. Is there a specific tool for this that fits into a drill? Something that could be borrowed from O’Reilly’s or AutoZone?
Remember to mark where the distributor rotor is pointing with a piece of tape or some such before you pull it !
Another question regarding the oil pan gasket and RTV
I've read conflicting reports about the FelPro Permadry Plus gaskets. Some have said they are the best thing since sliced bread and don't leak at all. Others said that they still had to apply some RTV sealant at the 4 corners. I'm not sure if they mean the 4 outermost points (rounded corners) of the pan or if they maybe mean the 4 points where the flat part of the gasket turns and rises (sinks) to fit around the ends of the crankshaft.
So, which "4 corners" do they really mean and do you guys recommend applying any RTV at all?
I've read conflicting reports about the FelPro Permadry Plus gaskets. Some have said they are the best thing since sliced bread and don't leak at all. Others said that they still had to apply some RTV sealant at the 4 corners. I'm not sure if they mean the 4 outermost points (rounded corners) of the pan or if they maybe mean the 4 points where the flat part of the gasket turns and rises (sinks) to fit around the ends of the crankshaft.
So, which "4 corners" do they really mean and do you guys recommend applying any RTV at all?
They mean where the parts of the gaskets come together if you are using the 4-piece gasket. Thats where the parts all come together - bearing caps, timing chain cover, etc. Thats why some guys still feel the need to use a little RTV here. I usually don't.
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theres a lot of thing s I would do before wasting my time pulling a pan now having an oil pan leak.
check your oil level..
pull a valve cover and start you engine and see if there is any oil coming up through the push rods or use a pump spinner to do it. Mark your distributor location so you can get it timed again if you use a spinner.
pull the oil pressure line and run the motor and see if oil comes out of the line into a can...it should spurt out..if it doenst make sure that line isnt kinked
pull your oil filter and cut it open and see if the filter element has collapsed
if it was a fresh block from a machine shop I would suggest one of the other oil gallery plugs but I doubt any of those will come out..If all that fails then you will have to pull the pan which will also screw up your timing chain cover lower gasket so you will need to replace that as well. You should invest in a felpro one piece gasket. You can pull it in the car but you will have to move the steering center link and the idler arm to get the pan to drop.
The "Four Corners" of an oil pan gasket are prone to leak. Looking at the bottom of the block, the area that holds the pan is flat all the way around until it comes to a main bearing cap. There is the first corner. Then on the other side of a main is another corner. 90* bends. Two on the front. Two on the back.
Even a One-Piece Pan Gasket should get a dab of Permatex Black in all four corners.
Suggestions welcome regarding oil pump and spin-on filter choices
First of all, I just discovered that the Purolator PL15313 oil filter I have installed does not have a bypass relief valve. If I understand this correctly, if the filter were to become completely clogged with debris, that would mean no oil would flow through the system ... unless the bypass valve at the oil filter adaptor plate opens up. Do I understand that correctly?
I haven't pulled anything apart just yet but I'm looking ahead and trying to determine what decisions I'll have to make.
IF I end up needing to buy a new oil pump, what brand/model would you recommend for my '73 350 SB? I've seen ones with bolt-on pickups which seems like an EXCELLENT alternative to the tap-in pickups I've seen on others. And, yes, I've read where people said to spot weld a tap-in pickup into place as insurance so it doesn't fall out. I don't have a welder so I'd be more inclined to go with the bolt-on alternatives.
Since the filter I used does not have its own bypass valve, I'd like to switch to one that does. What spin-on oil filter are you guys running with your 350 SB engines?
Last edited by sschultz2929; Feb 20, 2024 at 01:51 PM.
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Originally Posted by sschultz2929
First of all, I just discovered that the Purolator PL15313 oil filter I have installed does not have a bypass relief valve. If I understand this correctly, if the filter were to become completely clogged with debris, that would mean no oil would flow through the system ... unless the bypass valve at the oil filter adaptor plate opens up. Do I understand that correctly?
I haven't pulled anything apart just yet but I'm looking ahead and trying to determine what decisions I'll have to make.
IF I end up needing to buy a new oil pump, what brand/model would you recommend for my '73 350 SB? I've seen ones with bolt-on pickups which seems like an EXCELLENT alternative to the tap-in pickups I've seen on others. And, yes, I've read where people said to spot weld a tap-in pickup into place as insurance so it doesn't fall out. I don't have a welder so I'd be more inclined to go with the bolt-on alternatives.
Since the filter I used does not have its own bypass valve, I'd like to switch to one that does. What spin-on oil filter are you guys running with your 350 SB engines?
Why not try your local Chevy dealer, they may still stock OEM parts. Many are still available & or A/C DELCO replacement parts for correct & best fit.
After all, in the end it is a Chevrolet SB 350
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Concerned...
If I understand this correctly, if the filter were to become completely clogged with debris, that would mean no oil would flow through the system ... unless the bypass valve at the oil filter adaptor plate opens up. Do I understand that correctly?
