Recurring Sudden Oil pressure drop

D

daltonathomas94

Member
The oil pressure starts around 10-15 for about 30 minutes of driving every time I start, however if I ever pick up passed 50mph the pressure drops to zero. My gut says something is in the pan and getting sucked up to the screen, then falling after the engine sits for a while.

Any thoughts before I drop the pan?

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what year engine? what weight oil are you using? does it have a filter? oil pressure is low to begin with, have you checked for gas in the oil?
 
Check for mismatched oil pan, dipstick tube and dipstick. Drain the oil, fill with the desired amount of oil (4 or 5 quarts, someone will advise) and check on the stick.

My coupe had similar symptoms. I was too low on oil. I had to raise the level by 3/4".

In my case at sustained higher speeds, the oil would not drain back through the motor quick enough and the pressure would drop. Adjusting the level (up) solved the issue.

Mart.
 
It does sound like a restricted oil pick-up. As engine speed increases, so does the volume of oil pumped. Ten to fifteen pounds at any speed above idle is low. We don't know any details about the engine, but if it is an older engine the oil pick-up screen could be stopped up.
 
To start with only 15 to 20 PSI thats already to low when the oil is cold. Theres a a number of questions needing answers to try and figure out whats happening.
1- Is this a recent rebuild?
2- If yes to question 1 is there an engine driven fuel pump?
3- If no to question 2 is there a plug in the fuel pump push rod hole ?
4- Is the oil plug installed behind the cam gear ?
 
I do apologize that I am new to early v8s. Only experience is with the in line L6 from studebaker.

1-Rebuilt in the 80s
2-Fuel pump on oil filler neck
3-Should mean no to the plug
4-Unsure

I'll probably just end up dropping the pan anyway, I did a recent oil change, but the previous owner didn't seem to follow any sort of maintenance. Heck, the radiator was just tap water and the Dif plugs are frozen.

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There is an oil pressure relief spring under the intake - someone more knowledgeable than I can tell you how to get to it. This might be your problem as it gets weak with time and age. I resolved my similar issue by installing a 50 lb spring - they come in either 50 or 80. Now my oil pressure is nearly 50 lbs at speed and drops to no less than 15 lbs at hot idle. There’s a thread on this board describing how I chased it down to that spring ..... that thread would help show you what to do if nothing else
 
daltonathomas94 said:
I do apologize that I am new to early v8s. Only experience is with the in line L6 from studebaker.

1-Rebuilt in the 80s
2-Fuel pump on oil filler neck
3-Should mean no to the plug
4-Unsure

I'll probably just end up dropping the pan anyway, I did a recent oil change, but the previous owner didn't seem to follow any sort of maintenance. Heck, the radiator was just tap water and the Dif plugs are frozen.

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Click to expand...

No need to apologize the areas you need to look at are easy to help guide you on Im glad to help. Tom in post 11 mentions the pressure relief plunger/ spring thats located under the intake manifold. Removing the intake to check the spring would be the next thing to look at. You will see the plug located at the front of block under the intake. Maybe the spring is broken or just weak. If the spring is still visually good you can just stretch it a lot put it back in and see if that helps. You will notice what looks like a round ball end on this plunger assembly but this ball actually has a small flat spot on the side/bottom this allows oil to bypass all the time to feed the water pump bushings. If the water pumps are the newer type with bearings on the shaft they no longer have bushings requiring this oil feed. I put a ball bearing in this hole to eliminate this relief location I put the plunger/spring assembly back in to hold the ball in place an increase in pressure results from this oil passage now being closed. If you have the old type pumps and the spring modification making it longer did not help. It would seem theres an issue internally. Are you using an add on mechanical oil pressure gauge for the readings Im just wondering on that since no matter how your getting the readings your seeing it drop to zero so what ever is giving the readings I doubt is the issue.
When the engine requires more oil flow as the RPM increases the supply to the pump needs to be able to feed the additional oil needed. Its possible the oil pump pickup is plugged by sludge or maybe the pickup itself on the pump is loose {the pickup bolts to the pump}. Or maybe the pickup tube has a crack causing air to be sucked in at higher engine speed. To figure this out the pan will need to come off.
Ronnieroadster
 
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"Are you using an add on mechanical oil pressure gauge for the readings Im just wondering on that since no matter how your getting the readings your seeing it drop to zero so what ever is giving the readings I doubt is the issue."

Ronnie, wouldn't it be worth verifying the oil pressure before taking things apart? It most likely is not the gauge, but it is a quick, cheap check. At least that is where I would want to start.
 
JSeery said:
"Are you using an add on mechanical oil pressure gauge for the readings Im just wondering on that since no matter how your getting the readings your seeing it drop to zero so what ever is giving the readings I doubt is the issue."

Ronnie, wouldn't it be worth verifying the oil pressure before taking things apart? It most likely is not the gauge, but it is a quick, cheap check. At least that is where I would want to start.
Click to expand...




I agree checking with another gauge would be the best first step and cost effective.
 
I wouldn't mind having another guage in my tool collection so I'll definitely start there. Agreed in the cheap check, however in agreement with Ronnie, I doubt that would be the issue...

I'll go through your list after that Ronnie, as it seems concise and rather methodical. I'll start by draining the oil, but even then I doubt it will be soon.

Thank you all for your responses. You always make me feel welcome as a new member and new to the Ford side of the classics lifestyle.

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Dalton, when you drain the oil make sure you have the means to measure how much comes out. If less than 4 quarts the basic level/amount of volume could be the issue. I have experienced this, so please make sure you do check.
 
TomT/Williamsburg said:
There is an oil pressure relief spring under the intake - someone more knowledgeable than I can tell you how to get to it. This might be your problem as it gets weak with time and age. I resolved my similar issue by installing a 50 lb spring - they come in either 50 or 80. Now my oil pressure is nearly 50 lbs at speed and drops to no less than 15 lbs at hot idle. There’s a thread on this board describing how I chased it down to that spring ..... that thread would help show you what to do if nothing else
Click to expand...

There can be several pressure relief valves that will open and drop the
pressure to almost zero. One is up in front of the valve valley as mentioned.
And one in the oil pump. Older pumps with a smaller straight shaft housing
don't have relief valves. Once they open they stay open until the engine is
shut down and restarted but will dump again when the pressure gets up.
If the spring that controls when the pump dumps is weak stretching the
spring is not good as it go's weak again. A short spacer about 3/8" long
solves the problem. The length of the spacer controls the maximum
pressure. You need to make an oil pump tester, remove the drive gear
and run with a 1/2" electric drill. The pump works in the direction the drill
runs to drill a hole. The tester body is bored out so it pushes tight over
pump OD. A bad pump can pump oil with no load on the output like the
pump has pushing oil through the small clearance in the bearings. Bending
the plastic output hose acts like restriction the bearings put on the pump.
On a good pump the tighter you bend the hose the higher the pressure
shows on the gauge. You can use this to set the max pressure on the pump
by adjusting the by pass valve in the pump. The front valve valley valve can
be adjusted by removing the spark plugs and spinning the engine with 12
volts. The pressure you set the front valve at is the oil pressure you will
have at 45 to 50 MPH on the road. I normally set the pumps for 65 lbs.
G.M.
 

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