Clogged pick-up or oil pump failing?

I'm working on and LA 318. It has an after-market oil pressure gauge. I was driving home and thought I heard a quiet tapping sound around 3000 RPM. After about 30 seconds I could tell it was a tapping sound and I looked at my oil pressure gauge and it was bottomed out at zero. Immediately shut the truck off and coasted to a stop. Went and check my oil which was just fine and full. I went to restart the truck and no oil pressure again so I shut it off. I waited a couple minutes and tried again and the oil pressure went right up to 35 as normal. I drove the truck home with perfect oil pressure and then parked and took off valve covers and there was no signs of sludge whatsoever or blocked drain holes.

Since then the oil pressure will drop randomly and I'll turn the truck off immediately and roll my steering wheel around side to side then turn the truck back on and the oil pressure goes right back up to normal again. Is this the sign of a pickup tube getting clogged up with gunk in the pan or the oil pump failing?

I'd probably try a new gauge first.

Lifters clacking support no oil pressure, doubt it's the gauge.

Doesn't really matter if it's a clogged pick up or the oil pump. Your gonna have to drop the pan.

If it's is a clogged pick, question is what clogged it? Hopefully it's not the nylon teeth of a silent timing chain setup. You mention it's a truck (no real details there BTW) dunno if trucks got that setup or not, but who knows what someone might have put in there.

He said 'quiet tap', lifter rattle isn't quiet. And how old is the gauge?

with the tapping coinciding with the zero gauge reading (if I am reading that right), it definitely has an actual psi issue. I'd replace the filter (no fram) first & if no relief (you might get lucky) but I'm thinking the screen is plugged & unfortunately you know what that means (pull pan).

Depending on the truck, some have easy to remove pans. Sure sounds like clogged screen.

Sorry Supercuda I was hands free speak-to-text'ing this thread over my phone while driving and was paying more attention to the road.

Its a 1980 d100 with a 318, manual transmission. Just bought it a couple weeks ago. It was nice enough, had some nice parts in it, and it was dirt cheap, no issues at time of purchase.

It has a 2 barrel intake, a small holley 2 barrel carb (havent even looked at size), MSD 6A, cheap headers, full single exhaust with muffler, low pressure aftermarket out of tank fuel pump. The PO said the engine use to have aluminum heads and a big cam, but that cam got flattened and destroyed so he removed the heads and cam and put the stock iron heads back on and a new cam slightly bigger than stock. He also said the cylinders looked good as well. He changed the oil and filter but didnt remove the pan. I didnt nit pick and grill him for more detailed info, as he was selling me the truck for $700 and it had over $1000 in ignition, carb, headers and exhaust. Even if the engine didnt run it still wouldve been a good deal.

It has a jacked up throttle cable but other than that it has not given me any issues. The oil pressure problem started earlier today. Although it will drop randomly, I noticed it will do it if I come to a hard stop. Sometimes when I stop I'll just watch it gradually drop to about 10lbs, then slowly to zero. Thats what made me think there's crud in the pan and its getting sucked up and clogging the pickup tube, and when I shut the engine off and shake the truck, it disturbs the clog and things go back to normal until it clogs again. It could be debris from the destroyed camshaft as well (if that even happened).

The pressure gauge is the type with a tube that has oil in it from the engine. I can watch it go dry when the gauge goes to zero.

Could be a few things, IE: Junk oil filter, or sticking bypass valve on the pump itself.
I would suggest a new pump, oil and filter if you're trying to "SAVE"
it.
Keep rolling the dice and you'll get all of those with a replacement motor,

TJP, it just started happening today, Im going to drop the pan tomorrow and take care of business. The motor runs really well and theres no point in sacrificing it. What I meant in the earlier post was that the price was so cheap I didnt grill the dude about specifics, and the truck is worth more with no engine at all than the price he sold it for. Doesnt mean I dont care about this engine, it would be a waste to be reckless with it and lose it

My Durango would occasionally read zero at idle. Didn't think much of it as I didn't hear any ticking, etc. It's got a lot of miles on in, and I don't change the oil like I should. Assumed it was just the sender. At some point I finally changed the oil on it and a few months latter, I realize the gauge hasn't acted up in a while. Guessing I had a bad filter. That was probably a year or two ago, and now I've got 300K on it. For what it's worth, I think it was a Puraltor filter on it.

This oil gauge is not faulty. When the gauge gets down to zero I literally can watch the motor oil disappear from the small diameter clear tube that brings it to the gauge. And after about 30-60 seconds the engine starts making a tapping sound that changes with engine speed. So Im going to be very surprised if I don't find a bunch of crap in the pan and/or on the face of the pickup tube

I was saying that I thought I had a bad sender, only to find out it WAS the oil filter like others suggested.

Ok, that would be nice if that was my problem, then just an oil and filter change would be necessary. What did your filter look like when you removed it?

I suspect that you may have a contamination problem "somewhere". Oil filter, oil pump, oil pick up and fouled pushrods are all possibilities at this point. Does your "ticking" come and go and correspond to your oil pressure drops directly? To me it sounds like something is working under pressure and intermittently failing. If the ticking doesn't correspond to drops in oil pressure, I'd check for good electrical contact at your oil pressure sender just to eliminate that as a possible source of future annoyance. Changing the oil and filter might be a good place to start. have a good close look at the used oil to see if there might be something odd about it,

My sender is mechanical, no electrical connections. Yes the ticking came on with the drop in oil pressure, and went away as soon as the pressure came back. I figured originally that something was getting clogged, and to drop pressure in the whole system my first thought was the pickup tube. Thought the bypass in the filter wouldnt allow clogging. Then I realized Ive never actually seen an oil pump fail, so I posted here for more info

I'd start with these suggestions first. If you see evidence of contamination, I'd consider flushing out the system with a product and then fresh oil and quality filter to begin. If you don`t know the quality and grade of the oil that was put in there before you bought the truck, I`s suspect it starting now.

I bought a 1984 truck with a 75000 mile 360 on it from a local dealer. I talked to the previous owner who was a Penzoil faithful and told me how he changed the oil every 3000 miles. The dealer changed the oil before I bought the truck. It lasted about 1000 miles before the detergent motor oil they put in dissolved all the Penzoil buildup and stopped up the pickup tube. I was 100 miles away buying the Cummins diesel to go in the truck when my oil pressure started dropping and my lifters started clicking. I barely made it home. It maintained around 10 psi if I kept it below 50. It shuttered and seized up when I pulled into the driveway at home. I still have the motor. It looks like someone filled the valve cover with black cornflakes!!! Check the filter first and then check the pickup. My first wife's mini van did the same thing when I put in some Lucas oil treatment. It dissolved the Gastrol buildup in little flakes that clogged the pickup tube. It lost down to 10 psi and the lifters really made a racket. I dropped the pan and cleaned out the pickup. I dropped a bearing and it was fine so I cleaned her up and all was well.

I bet the valve seals got hard and cracked into pieces and fell down into oil pan and clogged the pick up screen. How do I know this?

This will relate to no oil pressure. I seen it several times over the years.

Not long ago I worked on a customer's car with the same symptoms... Turned out to be the fuel tank - Yup...

Rusty ass fuel tank kept sticking the Holley needle valve open, flowing a river of fuel, made it "challenging" to start.. Also destroyed the blue rubber 1-piece pan gasket and about a handful of blue rubber was collecting on the pick up screen. Wish I had a picture, it was an unbelievable amount of rubber - especially since the pan was still not leaking !

Never did cut open the filter on the Durango, but over the weekend I did cut open the filter on my Dart as the oil light started to flicker at idle whick it hadn't done before. Found all kinds of curd in there. Previous owner resurrected it after sitting for years before I bought it and I suspect dried out sludge working loose, and the above mentioned valve stem seals might be it's problem.

I once bought a 5th avenue for $300 that had the oil idiot light blinking on and off. Took the oil pan off and the pick up screen was full of the broken off nylon teeth from the timing gear and other gunk. Cleaned it all out and problem was solved.

My car was working fine, BB engine just a few years old and always run fine and maintained. I changed oil & filter with a Napa 51515 filter, pressure normal for about 30 miles then zero pressure on mechanical gauge. I check the drive gear and it was fine, removed valve in pump on BB and it was fine, no grit in there. Still zero pressure. I tried a new filter and pressure came right up, nd has been fine for years now. Bad filter somehow. Try that first and see.

1. Well, the tapping upon gauge loss of oil pressure indicates that it really is low oil pressure.

2. Most oil filters have a bypass that lets oil around the filter when the filter can't pass enough. So unless you specially bought a filter with no bypass, it isn't the filter.

3. I've never heard of gunk INSIDE an oil pickup tube

4. The scenario of stuff clogging the pickup SCREEN is plausible.

5. ALL commonly sold motor oil has detergent in it. So the idea of a "detergent" oil cleaning up an engine that had only been run on "non-detergent" motor oil is just plain wrong, unless one is starting an engine that hasn't been run for more than a half century.

6. Diesel lubricating oils have high levels of detergent because the oil carries a truckload of soot

7. My initial diagnosis was sticking bypass valve in the oil pump. That would explain the on/off nature of your problem.

8. DO change the filter first, it is inexpensive and easy to do. Then drive the truck and see if it happens again.

9. If that doesn't work, you have to drop the pan. While you're in there, change the pump. I have wasted two engines because I didn't change the pump. The original oil pump looked fine, but once engine warmed up, oil pressure went to around 5 psi.

10: To check the condition of rod and main bearings, look at the #1 main and the #1 rod journal. As these two bearings get their oil last, they are the first to go. My second 318 crank is reusable except the underside of the #1 throw is terribly ground down. The #2 rod bearing was perfect. On the same rod journal I had both no wear and extreme wear.

11. One of the culprits I see here at work all the time is shuttle valves sticking because of varnish buildup.

R.

R.

Pull the pan. By the time you go through all the "easy" stuff you won't have any engine left. The fact that the cam went south for the PO and he didn't pull the pan is a red flag.

+1, The previous owner already told you the engine ate a cam, so, all that metal clogged his filter, it bypassed due to the clog sending unfiltered dirty oil through your engine. Your oil pump took the first hit, it probably looks like it's been sand blasted internally. The metal filings have your oil pump pressure valve sticking causing your pressure variations. Before running the engine any more drop the pan, replace the pump, check your main and rod bearings to see how much damage they took. You may get lucky and find the bearings aren't too bad but I'd say they received some damage too.

Might help if you bleed the air out of that clear tube going into gauge. If there's air in the line the gauge doesn't read properly. Just fire up the motor, crack open the line at the gauge and when you have oil escaping without air bubbles tighten the line. Let's see what the gauge reads after that.

Yup. Experienced exactly this on two different LA engines. Identical symptoms to the OP...

Sob the oil pan is clean. Guess it'll be nice to have a new pan gasket lol.

I'm gonna disconnect the tube and see if anything is inside

I would say that I should've just taken off the filter 1st, but I know myself and even if the filter is the clog point, it would've constantly bugged me that I didn't know if the pan was clear or not.

Next step, off with the filter

My filter

I believe that it filters from the outside to the inside. What does it look like between the pleats? Given how white it looks doesn't look like the filter was in there that long.

Yeah and I just disassembled and cleaned the oil pump and pick up and there was no gunk in the pickup tube at all... I blew out every passage I could with compressed air and nothing sounded blocked up. So besides the possibility of the oil pump itself failing which I don't think it's likely because how randomly it fails, I'm stumped on the problem

Really hoping I don't have little tiny pieces of camshaft crammed in the tiny oil passageways in the block

Did you pull the bypass out of the pump?

It takes only a very very small piece of debris to make it stick.

Believe the gauge........ It coincides with the lifters clattering.

If you already have the pan off, just replace the pump. It's cheap insurance.

Okay, now before you do anything rash think about what you have found. If the pump is good (including the relief valve), the pickup screen and tube are clean with no cracks, and the oil pump drive gear isn't slipping on the shaft, the oil pump HAS to work. It has no choice. There is still something there.

Possibly, the oil pump drive shaft is slipping inside the drive gear?

When you're ready to re-install a new oil filter, don't cheap out. Go with a quality filter. I'll recommend K&N,Mobil 1 or Wix.Your oil pressure gauge seems to be working perfectly.

I repeat: replace the pump, even if it looks OK. You can get a brand new Melling or Enginequest pump from Rockauto for less than $40 delivered. I took a chance on an Enginequest pump when they were on clearance, it is the same casting as the Melling and is made in USA. High volume will run closer to $70.

It still sounds to me like the oil pump pressure relief valve is sticking open occasionally. This allows for the pump to be working which we know it is, as some times the pressure is where it's supposed to be. Then the engine speeds up to where the bypass opens and the little piston sticks. Now as you slow down the pump pumps less and the bypass is still open. Most of the oil from the pump goes right back into the sump.

On to checking bearings, I'll also repeat you should pull the #1 main and the #1 rod cap and look at the bearings and journals. If they are OK, the engine didn't suffer any permanent damage.

R.

Sorry for late reply. Shaft looks good.

Pump being replaced along with Oil with a little zinc, and decent filter.

When I smelled the oil it smelled like gas. Then I realized the pump is on or off only, so when the key is on, the pump is on. Could had been flooded many times by the po, and myself. The gas in the oil could explain the surprising cleanliness of the crankcase and head. Maybe a lack of lubrication messed up the pump and also caused the ticking?

I'd make sure the fuel pressure isn't too high, blowing by the needle and seat.

Are small 2 barrel holleys pretty common on fuel pressure requirements? I can get a refulator if necessary, what should the psi be?

About 4.5-5.5psi.

Having fuel in the crankcase will thin the oil out and your viscosity will be almost nothing. I encountered that with a small block Ford years ago when the diaphram in the fuel pump ruptured and filled the pan with gasoline.