Oil pressure drops to 0

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Craig Burriss

Craig Burriss

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I’ve finally gotten my car on the road and have been driving it everywhere for the past month. Today I fired up the 440 and was letting it warm up before I started driving it as I always do. The oil pressure when cold is usually at 70psi and when it’s at running temperature it’s usually around 30.
Well today, I start it, oil pressure goes up to 70, then starts dropping fast. I immediately shut it down and checked to see if my oil line had popped off. It had a small leak to I put some thread tape on it and fired the car back up. This time the oil only went to 60psi then dropped down to 0 almost immediately. The car has 6qts of fresh VR1 10-30 oil in it.
Could this be a faulty gauge? Or am I going to have to pull the engine AGAIN?
 
Craig Burriss said:
I’ve finally gotten my car on the road and have been driving it everywhere for the past month. Today I fired up the 440 and was letting it warm up before I started driving it as I always do. The oil pressure when cold is usually at 70psi and when it’s at running temperature it’s usually around 30.
Well today, I start it, oil pressure goes up to 70, then starts dropping fast. I immediately shut it down and checked to see if my oil line had popped off. It had a small leak to I put some thread tape on it and fired the car back up. This time the oil only went to 60psi then dropped down to 0 almost immediately. The car has 6qts of fresh VR1 10-30 oil in it.
Could this be a faulty gauge? Or am I going to have to pull the engine AGAIN?
Click to expand...
Quite honestly, only you're going to know if it's a faulty gauge.
 
I had an oil pump drive shear off once, was horrible...… replaced all the bearings on my back under the car. even got lucky and found all the pieces of the broken drive.
luckily I was only a block from the house when it happened.
 
Either the oil pump gear has sheared the pin on the shaft or the shaft has broken. It's only getting pressure because it's hanging up every now and then and turning the pump. That's my theory and I'm stickin to it. lol
 
Just used an older gauge to see if there was any change. Still the same...
Guess I’ll pull the distributor and look at that
 
If a piece of loose debris plugs the sensor inlet under pressure, the gauge can drop to 0.

This also happens with debris like old valve stem seals come apart & plug the inlet to the oil pick-up screen.

Sucked in under pump vacuum, then it falls away with the engine off.
 
The distributor/oil pump shaft looks perfectly fine. I guess now I’ll take the pressure gauge port off and try to blow any possible trash out.
 
Craig Burriss said:
The distributor/oil pump shaft looks perfectly fine. I guess now I’ll take the pressure gauge port off and try to blow any possible trash out.
Click to expand...

Triple check the gear on the shaft. I have seen one look fine but sheared slap off. You cannot tell either on some, Other than clamping the shaft in a vise and trying to tap the gear off to see if it moves.
 
With the distributor out rotate the pump with a speed wrench and see what it feels like. If you can build pressure you'll feel it. You could have an issue with the relief valve or some other problem inside the pump. Hard to say without some more debugging work on your end.
 
RustyRatRod said:
Triple check the gear on the shaft. I have seen one look fine but sheared slap off. You cannot tell either on some, Other than clamping the shaft in a vise and trying to tap the gear off to see if it moves.
Click to expand...
That’s a good point but if that happened wouldn’t the distributor stop spinning as well?
 
While the distributor is out, and oil pressure port removed, I primed the oil system with this contraption and made a huge mess when it came blowing out of the port. I then hooked the gauge back up and primed the oil system for probably 45 seconds at 70psi and it didn’t drop at all. I’m going to reassemble everything and fire it up to see if it still does it.
729C7453-3750-476C-8F46-B40EA91AD640.jpeg
 
I know you didn't find it funny, but I did! Ya, it will blast out of that little hole faster and higher than one could imagine!
You'll be able to laugh about it later on, maybe not right now though.
 
Started the engine and it’s still doing it...
Starts at 70 and stays there for about 30 seconds and then drops quickly down to 0.
 
Oil pump pick up screen debris from a 383 I just took apart, even more came out of it in the parts washer;

plugged pickup screen.JPG
 
Another thing that can do it is overuse of RTV. Chunks can come loose & the oil pump can pick them up in the screen.

Just enough weight to drop away with the engine off.

Chunks of gasket can do it too.
 
I’d try a different filter before I went too far.

It could also be an issue with a cracked/broken pick up tube/screen.

If it’s not the filter, drain the oil and fish around in the pan through the drain plug hole with something like a long thin screwdriver or a telescoping magnet to see if anything is rattling around in there.

What oil pump situation are you running?
Internal or external line?

If external, I have seen a problem with one of the external pump covers allowing the relief valve to travel too far, and get cocked in the bore....... stuck in the full bypass mode........ then you have little to no pressure.
 
PRH said:
I’d try a different filter before I went too far.

It could also be an issue with a cracked/broken pick up tube/screen.

If it’s not the filter, drain the oil and fish around in the pan through the drain plug hole with something like a long thin screwdriver or a telescoping magnet to see if anything is rattling around in there.

What oil pump situation are you running?
Internal or external line?

If external, I have seen a problem with one of the external pump covers allowing the relief valve to travel too far, and get cocked in the bore....... stuck in the full bypass mode........ then you have little to no pressure.
Click to expand...
It’s a Melling factory style high volume pump. I guess I’ll pull it off and inspect it next
 
I'd put a new filter on there before I pulled the pump. You could have a drainback valve that is defective or something along those lines. Cut the old filter open and see if there is anything inside. If a new filter doesn't solve it then pull the pump off and open it up for inspection. If you can't find a problem in either the filter or the pump then the pan will probably need to come off.........
 
Had a Fram on a SBC give me a scare once. Never believed a filter could make a complete loss of Oil pressure but that was the problem....

JW
 
I drained the oil and cut open my K&N filter. Everything looked perfectly normal.
If a new oil filter doesn’t solve the problem, what should I look for in the oil pump? Broken parts or scared surfaces?
 
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