1966 chrysler 300 / 383 sudden oil pressure loss

Bryon Mason

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Rebuilt engine, maybe 2k miles on it. Would randomly lose oil pressure when i Would "goose" the pedal at low RPM under 15mph. Recently while taking a corner , maybe 20 MPH, oil pressure dropped and never recovered. I shut the car down right away and had it towed home. So far I've pulled the distributor and checked the oil pump gear, replaced the oil pump, dropped the pan, pulled the pickup tube, cleaned it thoroughly. Reinstalled everything and still no pressure. I have the original "dummy light " and a mechanical Guage under the dash. Both show no pressure. Anything im missing before i tear into the engine? I did find some trash in the pickup screen and thought it would fix the issue. Im going to pull the pump again. Pack with petroleum jelly and give it one last try.

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Why is the oil is the oil pan so dark?
how many times have you changed the oil in the 2000 miles?

take out the relief valve and make sure it’s clean and moving free. Then prime with a drill. You don’t need to pack it with Vaseline.
 
The pump creates volume, the clearance between the bearings and crank create the back pressure you see on the gauge. Take #1 main cap off, check the tolerance with plastigage. If it's okay, go to the next. The fact you haven't mentioned valve train noise suggests the volume is making its way to the top, but the bottom end is wiped out.
Just a guess, good luck.
 
Also check the lifter galley. A broken push rod will cause a lifter to pop out leaving you with zero or very low pressure. You can check this simply by pulling the valve covers and turning the engine over, if one rocker is not moving, that is the source of the problem.

Dave
 
Also check the lifter galley. A broken push rod will cause a lifter to pop out leaving you with zero or very low pressure. You can check this simply by pulling the valve covers and turning the engine over, if one rocker is not moving, that is the source of the problem.

Dave
Good point.

I've seen push rods pierce rocker arms and let a lifter pop out.

This is pretty easy to check
 
Would not a displaced valve lifter also result in a dead cylinder also?

Our '72 Newport 400 would light the light from a stop with a quick acceleration from the stop, after it got some miles on it. Never caused any engine noises, though. I would pop it into "N" and rev the motor lightly to get the pump to work and the light to go out.

On my '70 Monaco 383 "N", I could easily turn on the light, too. If the rear tires broke traction on dirt with a sudden 3/4 throttle application, after about two seconds, the light would come on. So I'd quickly put in "N", blip the throttle twice, light goes out, continue on down the road. That motor has the MP windage tray, too.

Both of these motors went well past 100K with the bearings they came with. No issues. B/RB engines oil the lifters first, THEN the mains. Although a restrictor can be put in the oil supply to the lifters to bias the oil delivery more toward the main bearings. Small Block Chevy oils the main first.

Why did Chrysler do that? In the later 1950s, a (possibly) large part of the Chrysler customer demographics might contain many "vintage" people, whose hearing was deteriorating a bit. Low frequency sounds usually are the first to go. So . . . how many times have you heard somebody older than you (back then) ask to have their motor oil checked as they heard a lifter ticking (or so they thought)? AND, Chrysler V-8s all had hydraulic valve lifters, on their standard V-8 engines. Plymouth and Dodge had some variations, I believe.

If that had been a small block Chevy, the thuds might not be heard until they were felt, possibly. Too late by that time.

In the mean time, you might look for a factory oil pan with a baffle over the sump. As in a Fury GT 440 6-bbl oil pan, for example.

Not sure why this issue became an issue with a rebuilt motor?

Is your dipstick and dipstick tube the original pair for the engine?

Take care,
CBODY67
 
Would not a displaced valve lifter also result in a dead cylinder also?

Our '72 Newport 400 would light the light from a stop with a quick acceleration from the stop, after it got some miles on it. Never caused any engine noises, though. I would pop it into "N" and rev the motor lightly to get the pump to work and the light to go out.

On my '70 Monaco 383 "N", I could easily turn on the light, too. If the rear tires broke traction on dirt with a sudden 3/4 throttle application, after about two seconds, the light would come on. So I'd quickly put in "N", blip the throttle twice, light goes out, continue on down the road. That motor has the MP windage tray, too.

Both of these motors went well past 100K with the bearings they came with. No issues. B/RB engines oil the lifters first, THEN the mains. Although a restrictor can be put in the oil supply to the lifters to bias the oil delivery more toward the main bearings. Small Block Chevy oils the main first.

Why did Chrysler do that? In the later 1950s, a (possibly) large part of the Chrysler customer demographics might contain many "vintage" people, whose hearing was deteriorating a bit. Low frequency sounds usually are the first to go. So . . . how many times have you heard somebody older than you (back then) ask to have their motor oil checked as they heard a lifter ticking (or so they thought)? AND, Chrysler V-8s all had hydraulic valve lifters, on their standard V-8 engines. Plymouth and Dodge had some variations, I believe.

If that had been a small block Chevy, the thuds might not be heard until they were felt, possibly. Too late by that time.

In the mean time, you might look for a factory oil pan with a baffle over the sump. As in a Fury GT 440 6-bbl oil pan, for example.

Not sure why this issue became an issue with a rebuilt motor?

Is your dipstick and dipstick tube the original pair for the engine?

Take care,
CBODY67
Original dipstick, i had the same problem with losing pressure, neutral. Couple whaps of the throttle and pressure came back. I pulled the distributor and the oil pump drive shaft. Run a hex rod to the drill, pulled the oil sending pressure unit, it pumps oil to the unit at the back of the block but again no pressure, just oil flow. My thinking now is either a lifter or one of
the oil galley plugs failed.
 
Is the oil pressure gauge and the switch coming from the same tap on the engine? This pressure port could be plugged.
A sudden drop in pressure would be caused by something failing. Bearing wear and pump wear would be a gradual deterioration in pressure.
Spinning the oil pump through the distributor drive is a good strategy. I made a driver from a distributor shaft and chuck it in my drill.
 
Has there been any prior oilchange since the rebuild?
You could have an oil filter that's gotten plugged by some rebuild particles.
Theoretically, it should bypass, but I had one plug on me years ago.

Oil light came on unexpectedly, I turned car off and contemplated while I coasted.
Restarted to hear for knocking, but oil light went off, so I put in Drive and started back home.
It came on perhaps 15 secs later, so I shut down and coasted.
Lather, rinse, repeat the last few miles home.
Changed the oil and the problem disappeared. And the filter was HEAVY. (old engine, don't know what was in the filter, and engine was fine for years after).
That was the last time I used that filter brand.
 
Has there been any prior oilchange since the rebuild?
You could have an oil filter that's gotten plugged by some rebuild particles.
Theoretically, it should bypass, but I had one plug on me years ago.

Oil light came on unexpectedly, I turned car off and contemplated while I coasted.
Restarted to hear for knocking, but oil light went off, so I put in Drive and started back home.
It came on perhaps 15 secs later, so I shut down and coasted.
Lather, rinse, repeat the last few miles home.
Changed the oil and the problem disappeared. And the filter was HEAVY. (old engine, don't know what was in the filter, and engine was fine for years after).
That was the last time I used that filter brand.
I ran the break in oil for the first 500 miles or so, then changed the oil. I've now changed the oil and filter again since the pressure drop..
 
Should be able to get some NOS ones off eBay or maybe here or try 440 source, they seem to have good parts at a reasonable cost.
 

And the majority of the results on that search are hot-rod-aluminum-needle-bearing-ductile-iron adjustables-higher-ratio things he isn't looking for.
And an ebay link that will take him to all those things on ebay.
Or links to webforum results of people asking where to buy and install such things he isn't looking for.

@Bryon Mason
Rock Auto has some, made by Melling, but kinda pricey when you consider needing 16 total.
Does not say where made, but Melling has always been a good name in engine parts (Unless things have changed?)
When it comes to Left/Right - that refers to the offset of the pushrod pocket, not left/right side of engine. (but you'd buy a whole set, so not an issue)

1970 CHRYSLER 300 7.2L 440cid V8 Rocker Arm | RockAuto
 
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