since it's cold and snowy, My mind is wandering. maybe i'm missing something.need to attack this in the spring.
I'll try and keep it short with just facts.
1966 383

spring 1990 I buy a 1970 charger, drive for 6 months, pull it apart for rust repair and fresh paint. rebuild / freshen engine in summer of 1991 before going back into fresh painted car.
Quick hone,new cam bearings,wash engine thoroughly. new main bearings,rod bearings,rings, mopar 509 cam & lifter, new timing chain,oil pump,new gaskets.install engine,break it in.change oil, no problems, put about 1000 miles on it.
'Here is when the problem starts':
install 3.91 gears in place of 3.23. drive on the expressway,about 65mph,above 3000 rpm I saw the factory oil pressure gauge fluctuating real bad, first thought is factory gauge messed up,NOPE oil pressure went to 0 and I can here the lifters clattering. stop, the oil pump locked up and the intermediate shaft broke. replace pump and shaft,(melling pump) change oil (20 w 50 valvoline) and filter.(fram back then). all is well, good pressure and quiet. next time on e-way, gauge goes crazy again. slow down,all is good. drive car for the next 10 years,maybe put 5000 miles on it, avoiding the e-way.
2002: i'm going to try something, I have some extra money to through at it. Yank the engine out, install new 7 qt oil pan with pick up, windage tray,high volume oil pump, replace mopar 509 cam with a lunati cam and lifter set,( cam still looked perfect). upgrade cylinder heads,( 346 casting that had work done to them) install a 6 pack intake.20 w 50 valvoline oil with wix filter. ( i learned about the fram quality by then).
SAME issue when on the e-way. oil pressure gauge goes crazy. check oil and it's foamy.
Not sure what else to do, I tried mobil 1 synthetic oil. same problem.. I avoid the e-way, keep it 50 mph or lower I have no problems.

My last thought is this: I need to check the block, maybe it's one of those oversized lifter blocks, and i'm losing pressure there?or a crack internally somewhere?

I did everything myself, This was my first cam bearing replacement, I rented a tool, and was very careful about lining up the holes.If I installed the cam bearings wrong, I would think the first cam would have wear. all looked good.
What else am I missing??
Thanks

Are you using a stock pump or a high volume pump?

I'd borrow a radiator pump up kit & see if it will hold 15 psi cold & if it will I'd get it good & hot & pump it back up to 15 & let it set & keep tabs on the gauge & see what develops. If you have an emission testing station you could have them stick the probe in the air space under the rad cap & it'll register any hydrocarbons & either of those indicate a combustion leak into the cooling system. Not sure how that is affecting the oil psi but we gotta start somewhere.

Sounds like the oil is not draining back to the pan as fast as it's

going to the top end. This sometimes happens with HV oil pumps.

I might suggest starting with a GOOD mechanical gauge just to verify what you are seeing and when. Write everything down.
What is the pressure at idle when cold and hot.
What is the pressure at 2,000 and 3000 RPM when cold and hot.


you know that it happens at X mph in 3rd gear, what is the RPM???
How long at that RPM before the pressure starts dropping???
I might then try 500 RPM less and see what happens. Record the findings.
Repeat at 1000 RPM less.

One could then repeat the same process in second gear and finally neutral.
If all of the readings concur it would indicate that the pan is being sucked dry. The question is why???? my guesses would be excessive clearance somewhere or one of the internal oil galley plugs may be leaking.
Keep us posted

I have tried all 3 type of pumps the first failed pump was a high pressure. the second was a stock pump,I put a high volume pump only because of the 7 quart pan.I had the suck pan dry thought as well.

I have had 2 different set of heads on this engine, 906's, now has 346's,both times with standard felpro gaskets.

At 65 mph,rpm might be 3300 ish. the problem takes about a minute to pop up,slow down to 55mph, it stops.rpm are slightly below 3000. I never tried it on the normal streets in second,or neutral.
I know the gauge is believable, since when I did ignore it, the shaft snapped off,and the pump was locked up. I have checked it with a manual gauge, the factory dash was pretty close. 60 lbs cold, hot idle about 25 lbs, when the problem happens it's around 45 lbs. drops down to 10ish and back up and down. let off gas,slow down. it then stabilizes around 45ish.

Why the oil is foamy when it happens is what I can't understand. let it sit for a while, the oil is normal again. I'm sure it's not coolant.
I check all fluids before I take a cruise.

Are you sure all the oil passage plugs were reinstalled when you built the motor?

Oil is foamy? How much oil do you have in it? Might be too full and being splashed around by the crank. Windage try? Try a quart less.

My best guess would be the oil pressure relief valve. I am guessing it's sticking and therefore loading up the oil pump. That would make sense with the oil pressure variance. I would pull it apart and make sure nothing is in the passageways.

with more thought I'm thinking the pickup is too close or too far from the pan or not parallel enough and or the pickup is being partly uncovered when it acts up, that it is sucking air at that point in time tho I wouldn't think a 7qt pan would be getting "uncovered"

If it's doing the same thing, with a variety oil pumps and oil pans, and it did not do this before you rebuilt motor in 1990, then maybe it is excessive bearing clearance somewhere. Did you check all with plastigage when you rebuilt, rod and main?

Foamy oil is being aerated by the crank and rods at the upper RPMs, drain the oil out and put it back in quart by quart and recalibrate the dip stick to show when you have 7 quarts in the 7 quart oil pan the other thing already mentioned is the oil pick up, does it have the proper one for the 7 quart oil pan now? If not get that fixed right away Last thing is a windage tray, do you have one in the motor? If not you may want to get one to help control the oil return BTW, what brand is the new oil pan?

I can not say if the problem was there before I rebuilt the engine, it was not there after the rebuild. It only showed up after the the gear change to 3.91. a year later. I did not touch any oil galley plugs,only looked to see if they there were in place. possible to be an old problem.
Good thought on too much oil.I am not sure what I put in. I added until full.perhapes the dip stick is wrong. I might have 9 quarts in it.IT is Possible to be 1 quart over full. I do have a mopar performance windage tray installed.

I did plastic gauge it. it was on the loose side, hence the reason for the 20-50 oil. the rods and mains are .025 .

I triple checked the pick up clearance to the pan. No way it's wrong. I also used clay for mock up. within a 1/2/ inch. also has thread sealer on the pick-up at the block. the pan and pick up was purchased at the same time (same stuff that everyone uses,milodon, nothing custom or special)
3 different oil pumps. No way all 3 have the same problem.I used major brands, Never an off brand. pre-lubed with drill every time.

over filled has me really thinking. I could be 1 quart over. dip stick and tube was never changed. Maybe I have been a quart over. The extra rpm's from the 3.91 gears caused an issue.

I had this happen once on a freshly built bigblock stroker.
Windage tray, HV oilpump and a new chrome dipstick were used also.
The China dipstick didn't seat all the way into the block during installation. In fear of breaking it off at the time I left it seated about 3/4 up and tackle that later.
During startup I ofcourse had forgotten about that and overfilled the crankcase.

While breaking in the cam I started hearing a slight lifternoise and a fluctuating oil gauge, so I shut it down.
Checked the oil and it was foamy. The cam and lifters were still OK fortunatly.
Fixed the dipstick, rechecked the oillevel and drained about a quart and the problem was gone.

Sounds like too much oil to me.

I know on my 440 with 8 qt pan the dip stick is off.I run a hi vol hi press pump with 1/2 inch pickup.If I put 8 quarts in the dipstick reads wrong.Its a MP piece.I run 7 1/2 quarts in it.Its been together for 14 years and never a problem.OP is always rock solid even running 70 with 3.91s.My pickup is about a 1/4 inch from the pan with windage tray.I run 20 50 Kendall GT1.Rocky

Moretoys, definitely post what it ends up being. with an oddball pan I get the car (pan) level & add the # of qts the sump is supposed to have & whatever the dipstick reads at that point is "full" & I mark it there. this is with the eng not started & the filter out of the equation. 1/2" does sound like too much. We'll be waitin

Perhaps it is the pressure relief valve, as suggested eariler . . . on a 440 I had, first I had a leaky oil pump, no gasket between pump and block . . . changed that, then noticed low oil pressure - was a "new" Mopar Performance HV pump . . . changed that out for another and had HIGH oil pressure - high enough to blow the gasket off the oil filter !!! Finally changed out to stock pump (after market from Napa), and all was well . . . perhaps when you changed your diff gearing, it increased your RPM's to the point where the pressure relief valve opening and stuck ???

Mark