Can bad lifter(s) cause low oil pressure?

...Just what it says. I have a noise that I am convinced is coming from the top end of the engine. I am positive the valves are perfectly adjusted 1/2 turn past zero lash, the pushrods are the right length and straight, the geometry is right. In short, everything I can do under the valve covers to resolve this has been attempted.

The other symptom: Low oil pressure. Now, I know low oil pressure can cause noisy lifters, but that is not, I believe, what's happening here. Pressure is awesome when the engine's cold of course. It takes a long and/or rowdy drive to make the pressure drop, but yes, once the oil's heated up real good it idles at almost nothing and the gauge pretty much follows the tach until about 3k where I'm back up to a good 40 pounds.

This is with 20w50 oil, so of course I was thinking about bearings.

The lifter noise, (at least I think it's lifter noise - could be a rod knock for all I know but I swear it's coming from the top) does not happen during the first few minutes of driving. If I keep the RPMs down it may take quite a while to start hearing it, but if I spin it up a little it starts right away and it stays there, no matter what stage the oil is at. That's one reason I think that a lifter might be the primary and not a secondary symptom - that the sound starts after I get the RPMs up a little, not when the oil heats up.

Anyway, here's where my mind is at now:

I think I can get rid of this noise if I replace the lifter(s), but if this engine has worn out bearings and ultimately needs to come out and be torn down, I'm not going to waste the effort.

So... Is it possible that a defective/collapsed or otherwise "bad" lifter could be causing my oil pressure drop? If there's even a remote chance that a lifter swap will fix both problems I'll do it, but if there's no hope of my oil pressure getting back to something acceptable then I'm just going to park it and start planning for the next phase.

 

A loose Main Bearing is a powerful dull thud or knock that take place regularly every other revolution. The knock can be confirmed by disconnecting the plug wire next to this cylinder. The knock would be less audible.

Loose Rod Bearing is a metallic knock that can be heard the loudest at about 30 mph. The knock can be reduced or eliminated by disconnecting the plug wire to this cylinder.

Loose Flywheel is a thud or click which is usually irregular. To test, idle the engine fast and shut off the ignition. If a thud is heard, the flywheel is loose.

Loose Piston Pin is a sharp double knock which is usually heard when idling. Severity of knock should increase when the plug wire is removed to this cylinder.

 

Chiltons and Motors say 3/4 turn past zero lash.

 

Ok, just to be sure then I will crank them down another 1/4 turn before I do anything else. I doubt that will have an effect but I do want to be thorough.

Of all the things you mentioned, this fits the symptoms a little better than the rest. The sound never happens at idle, and is mostly audible in the 2k RPM range. (once it gets started that is; it doesn't make the sound at any speed for the first few minutes) The sound also changes or goes away depending on throttle position.

I will start pulling plug wires and see whether it has an effect, but unless my ears are playing tricks or the sound is traveling through the piston or something, I really think it's coming from the top somewhere.

 

This sounds like the combination of the oil not returning to the pan fast enough ( I would ditch the 20w50 and go with 10w30 or even 5w30 and make sure it is plum full or even a little overfull) and I bet you have a high volume oil pump with a stock (5 quart) oil pan....

what is happening is while everything is thick and all drained into the pan the oil is returning to the pan just as fast as the oil pump is pumping it. once the oil is all in the upper part of the engine and thinned out to where the pump is pumping it faster than it can return to the pan your oul pressure starts to drop because there isn't any oil in the pan for the pump to pump. My 73 does this if it gets the tiniest bit low because it has a high volume oil pump and a 5 quart pan.

I have tremendous oil pressure when I start the car 50-60 pound or better get out running the back roads after the engine heats up and start winding the RPM up and the oil pressure goes up and down with the RPMs until the oil gets disperse throght the upper parts of the engine (very little in the pan) and then I hit a couple of twisty turns with the RPMS up and the oil pressure will drop off to nothing, let off the throttle a little bit, oil drains back into the pan and pressure pops right back up. kick the throttle and hit a couple twisty turns and oil pressure follows the tach until it gets dispersed through the top of the engin then it drops off again because there isn't enough in the pan to keep the pump constantly supplied. When I see this happening I can stop, check the oil level and it may only be 1/2 quart or less low. Put in a half quart or even overfill a tiny bit and the problem goes away because it is keeping just enoguh in the pan to keep a constant supply to the oil pump. Basically if the person that built the motor would have used a standard oil pump with the stock pan or put on a larger capacity oil pan with the high volume pump this would never happen.

Does this pretty much describe what is happening to you or am i way off base?

 

Reasonable theory, but unfortunately I don't think so. I did try running 5w30 at first and the problem was much worse with that. You're right about some of it though; I do have a high volume oil pump and a stock oil pan. Takes just shy of 6 quarts to put it on the full line. And the problem happens more after a good Interstate run for instance, but it doesn't get better when I get off the highway and idle. Once the oil pressure goes bad, it idles just above the peg and nothing's going to bring it back up other than letting it cool off.

 

Hmm. Believe it or not my Dad had a 1978 Ford truck with a 351w that did just what you are talking about. had pretty decent 30 or so PSI pressure starting from dead cold crankcase and would stay that way (like you said) until you ran it out on the highway and got it good and hot and then it would drop to almost nill. maybe a needle above "0" If you put it in park at an idle instead of in Drive with foot on brake it would come up to maybe 5 psi. The cause of it was the Main Bearings. He and a friend replaced the rod bearings when the engine had around 90,000 miles on it and maybe 15,000 mile later the oil pressure did this jacked up thing. He replaced the oil pressure sending unit (electric guage) and put a manual gauge on it (thinking it was the guage. Believe it or not he towed our camper from Maryland to Florida and back and drove the truck for several years with just that little bit of oil pressure. Then sold the truck and, my cousin drove it for years and years and never did a thing to it. Honestly I think the body on the truck gave up before the engine ever did.

Dad did however do just what you are doing and used Castrol GTX 20W50 or sometimes straight sae30 weight. He kept the oil changed religiously and would put a can of STP or Motor medic or Motor Honey in it once in a while but I guarantee that AFTER the oil pressure dropped (because of the main bearings) between Dad and the cousin we sold it to they put probably another 80,000 mile on it with the bad oil pressure.

Now I do not remember how Dad and his mechanic buddy ever verified that the oil pressure drop was because of the main bearings but i do know that they did verify it some how.

You know what the cause of this was? Before the oil pressure dropped Dad used Quaker State oil religiously/only Quaker State and it was during that period that they did something weird and had a paraffin base to their oil and it screwed that engine up something terrible. I seen the results first hand when I helped put valve seals in that engine and cleaned out gobs and gobs of sluggy, waxy, gunk from the inside of the valve area under the valve covers.

 

Sounds like a bottom end problem to me.
Not likely relative to your issue but a wierd one we had years ago on my buddies 289 was a sudden loss of oil pressure and real noisy lifters. It turned out that it spit out a gallery plug behind the cam gear. This was a constant loss of pressure though, obviously. Just popped into my head when i read this so i figured i'd post it. Good reason to thread the gallery plugs.

 

Yeah, this isn't constant... I get 65 or more PSI from a cold start, stays there for a good long while then once it's hot starts to go down until it idles between 2-5 PSI. After that point, cruising is pretty much 1k RPM = 10 PSI, 2k = 25 PSI, 3k= 40 PSI.

 

I had a 302 that did something close to that, it was the cam bearings. When I took the block to the machine shop, that's what he told me. Since the rebuild, it's been fine.

 

You have a bearing issue...Most likely mains, possibly cam bearings. Oil is flowing past the bearings faster than the pump can keep up the pressure. This loss of pressure also kills volume, that will starve the lifters causing them to clack. Any lifter noise is only a symptom, not a root cause. You need main bearings man. Good luck!!!

 

I had a similar issue with a rebuilt 302 in my 73. the center cam bearing rolled out over the journal and when it was hot, it wouldn't make over 4psi at idle. When it was cold, it did fine. The noise could be a lifter if the oil pressure is being lost before reaching it, especially if it was downstream of the leak. Just a thought.:16suspect

 

6 quarts in a stock Maverick pan ? One thing's for sure, the crank is also whipping the oil into a froth, you're a full quart over full here. A bad lifter will cause what you describe, when you check the rockers after it's warmed up, are the adjustments still in spec ? Nothing's loose ? If there is, then I'd suspect you've wiped a cam lobe, which will take the lifter too, wearing the bottom of the lifter until there's a new oil hole in the bottom.

 

The thing that has the biggest effect on oil pressure, as measured at the port by the oil filter, is the #1 main bearing clearance. That's why 289 and early 302 main bearing clearances are speced with #1 being half a thousandth tighter than the rest. Why on earth are you running 20w50? Are your bearing clearances over .003"?

 

I was running 20w50 because the oil pressure was terrible with 5w30. That's when I suspected wear damage, but I wanted to see if the thicker oil would help. Also replaced the oil pump...

6 quarts (nearly) in a stock 351w pan from a '78 T'bird...



So it looks like the general opinion here is that the engine's shot. That's about what I was expecting, but thought I'd throw one more idea out there before I give up.

I guess I'll have to either park it until the means to get another engine comes along, or just run it until it blows. No point in taking a .060" over block into a machine shop.

I pretty much spent what I had to spend on this thing getting the engine in there, so it's going to be a while. When I got this engine I heard it run, warmed it up and it didn't do this. Oil pressure was good so I didn't really tear into it that much except to install the cam, heads, etc. Probably should have let it warm up a little longer, hit the throttle a little more... Oh well. I gambled on a cheap engine and lost.