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75 lbs. oil pressure to ZERO in 10 seconds. WTF?

Mark Barnes

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Just fired my 383 last week. Started and broke in very well. New Melling hi volume pump made pressure 75lbs. at startup, drops to 25 lbs.at idle, 60lbs. at 2500 rpm. Took my son up to the parts store to get collector gaskets. Almost drove by the store driveway, so I leaned on the brakes a bit. Oil pressure went to zero, and stayed there. No clatter, no other noises. Shut the motor down, went inside, came back out 10 min. later restarted motor. Ran 5 seconds, no pressure. Shut it down again. Pulled the distributor, shaft is fine. Intermediate shaft, no issue, gears just like brand new. Cam too. Had it towed home. Only thing I can think of is brand new pickup tube broke off, or separated enough to suck air? (I have 2 oil press. gauges, one mechanical, one electronic, both said zero.) Never had this happen before...anyone have a similar issue? I'm lost and pissed. All brand new parts...
 
At first I would agree with the pickup... but when you say it's fresh with the good HV pump, the 25 lbs pressure is alarming.
Could still be the Crack at the pickup thread, but wondering if the pump got **** kicked with trash going through it.
 
If the cam bearing with three holes is tight and spins, won't it cut off signal to the guage pressure as well as the rocker train?
 
To continue with the last post, is the valve train noisy?

You could pull the drain plug and look inside the pan for an out of place pickup. Pressure valve in the pump might of stuck open too.
 
pull the valve covers off , pull the oil pump shaft and spin the oil pump with a drill, see if it's actually moving anything up top ? the cam bearing could have spun.
 
If the cam bearing with three holes is tight and spins, won't it cut off signal to the guage pressure as well as the rocker train?
No
20220712_155321.jpg
 
I just stuck the priming rod back down there and spun it...nothing. Pump or pickup, I guess...
 
I wouldn’t be to surprised at a cracked/ failing pickup - after just having installed one and having to use vice grips to spin it down tight and to clear the pan.
 
If the cam bearing with three holes is tight and spins, won't it cut off signal to the guage pressure as well as the rocker train?
Will just cut the oil to rocker shafts. Gauge will work.


@Mark Barnes drain all of the oil from the drain plug and see if any debris in the oil. Pour it back in if clean. Then remove the pressure relief valve from the oil pump and see if any debris in there. Then try the priming shaft again.


no need to remove valve covers yet.
 
Will just cut the oil to rocker shafts. Gauge will work.


@Mark Barnes drain all of the oil from the drain plug and see if any debris in the oil. Pour it back in if clean. Then remove the pressure relief valve from the oil pump and see if any debris in there. Then try the priming shaft again.


no need to remove valve covers yet.
This is perfect, have to change oil anyway. How does the pressure relief come out?
 
Pull a valve cover and double check the valve train, if a lifter collapses it will pop out a pushrod losing oil pressure..

Just my $0.02...
 
Pull a valve cover and double check the valve train, if a lifter collapses it will pop out a pushrod losing oil pressure..

Just my $0.02...
SFT camshaft/ lifters. If one of them collapses I have WAAAY bigger problems that no oil pressure!
 
it takes 10 minutes to take the 15/16 bolt facing the back of the engine and take the spring out and check the valve if it's free
 
Screen Shot 2022-07-12 at 11.10.36 PM.png


Relief valve could be hung open or a dozen other possible problems... A lifter out of it's bore, oil pump found a way to suck air, oil pump drive shaft sheared...

In your post you say "Intermediate shaft, no issue, gears just like brand new." did you actually pull the shaft & inspect it? Or looked & saw the gears look good? Cause twice I've seen the drive hex get sheared off...

Have you tried spinning the oil pump with a priming tool?
 
I hope it is just a stuck relief valve, but........

To check the pump p/up, remove the pump. Blow compressed air into the p/up passage in the block. If you hear air hissing, p/up has broken. If you here gurgling [ oil ], it indicates p/up is ok.
 
I hope it is just a stuck relief valve, but........

To check the pump p/up, remove the pump. Blow compressed air into the p/up passage in the block. If you hear air hissing, p/up has broken. If you here gurgling [ oil ], it indicates p/up is ok.
Maybe, maybe not... The hissing I agree, bad... The gurgling, doesn't prove there no air leaking it just means some air is bubbling in the oil, so the pickup isn't fully broken, but it could be cracked....
 
I'm not a fan of the aftermarket pickup tubes, I was trying to get mine positioned right and it snapped off at the threads with barely any force. It was one of the gold pickup tubes, looked to be cheap cast metal.
 
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