360 oil pressure question

-
440BelII

440BelII

Well-Known Member
Joined
Apr 26, 2008
Messages
1,099
Reaction score
121
Location
Darien Center, New York
We have a '72 Demon with a 360 that my son races . The car had some issues but lately has settled into being a 8.0 in the 1/8th mile car. It's been pretty much consistent since we brought it out this year. Last night, my son noticed the oil pressure guage was off from where it usually is on his first time trial. Usually, on a cold start off the trailer. it is a constant70 lbs., drops off a little when it warmed up but came up under rpms.Last night, it was fluttering between 50 and 55 psi,never really went any higher. I told him to not run it anymore until we find out what's going on. Today, I installed a oil pressure guage and we started it to rule out a faulty guage. It still fluttered between 50 and 55psi. So, my question is, what would make the oil pressure drop 20 psi and make the guage flutter instead of staying steady? My thinking,right or wrong, is that the oil pressure relief spring broke, causing pressure to slightly bleed off until it pushes against the spring.That's where I was going to start looking. The motor's coming out, no matter what, to check it out. Any opinions would be greatly appreciated. Want to try to hopefully get it fixed and back out for the rest of the season.
 
I think you have answered your own question, engine needs to be checked out. Hope for your sake it is just a broken spring, an easy fix, but I have a feeling....
 
I’d cut the oil filter apart also
If you see metal debris then a bearing might be going. If clean change the spring or whole pump and start it If back to 70 that was it.
 
Is that 70 at idle? I would drain the oil change the filter see if there are any concerns there. Then start it with new oil and see what it does. After you change the oil try a different gauge, 50-55 psi at idle isn't bad tho. But the fact that it dropped is concerning
 
I don't think it is a relief valve spring problem, have not seen any broken or weak. I have had the cotter pin shear, and the valve come out. That had no oil pressure. I would be looking for a leak somewhere, bearings, lifters, block plug.
 
Sterling said:
I don't think it is a relief valve spring problem, have not seen any broken or weak. I have had the cotter pin shear, and the valve come out. That had no oil pressure. I would be looking for a leak somewhere, bearings, lifters, block plug.
Click to expand...
Yea I agree with this if the oil pump relief gets stuck or fails you will have zero oil pressure.
 
Yes, 70 at idle on startup was the norm. I did change the guage already. I used an oil pressure guage kit and eliminated the one in the car to see if the guage was faulty. It still reads the same.
 
I'm just trying to understand the fluttering guage. It always would sweep up and read steady. It's not like it's a constant low pressure reading. It will go between 50 and 55psi at idle, which technically is more than enough to run the car on. We just know where it used to be and it's not the same.
 
My vote is rod bearings going away. Was there anything weird about his last run? Did he miss a shift, or over rev it, or anything like that? If it pushed out a lifter you’d know by the sound. Any noise in the engine at all idleing?
 
Nothing happened during his Time trial pass, other than the car ran way slower than normal. It ran an 8.70, as compared to the 8.0's it normally runs.No noticeble noise from it. I did do a compression check on it yesterday. All the cylinders came in at 155-160 except for #2, which was 145.
 
Drain the oil into a clean pan, look for metal filings.

Cut the filter open, look for metal in the pleats.
 
We drained the oil , not seeing anything unusual. Cut the filter open ,nothing again. As per a few suggestions, we're going to spin a new filter on, fill the oil, and see if anything changed.
 
That’s a good sign. Hopefully it is just a relief valve hangin up or something simple.
 
GO ahead and finish the oil change. That's how I tell the oil in my truck needs changing. When it doesn't quite have the pressure it once did. New oil and filter, pressure is right back up again. Those additives don't last forever. It's certainly worth a try.
 
What does the plug look like in the cylinder that is 145lbs? Super clean?
 
Could have pushed the head gasket into the valley and putting cylinder pressure into the crankcase. Which might make the oil pressure “show” weird things.
 
Could be a lot of things. I don’t think it’s the pump or the relief valve. I don’t think the spring could possibly break. It could be stuck slightly open. Could be the filter and the anti drain back valve.

If it has shaft rockers, the rocker shaft ends could pop a plug out or knocked itself sideways.

you could have water or fuel in the oil diluting the oil

if the car is slower and there is a misfire or even just a lower idle speed, the oil pressure will be lower. 20 psi is a lot tho.
 
in this case; .8 second is 10%. That seems like a lot.
Is that 360 a regular LA engine?
You call it a flutter but talk as if it's just drifting........ I mean I have no clue, but just want to get my thinking straight. Just curious; what is the idle speed?
 
T56MaxTorq said:
Could be a lot of things. I don’t think it’s the pump or the relief valve. I don’t think the spring could possibly break. It could be stuck slightly open. Could be the filter and the anti drain back valve.

If it has shaft rockers, the rocker shaft ends could pop a plug out or knocked itself sideways.

you could have water or fuel in the oil diluting the oil

if the car is slower and there is a misfire or even just a lower idle speed, the oil pressure will be lower. 20 psi is a lot tho.
Click to expand...
Sounds like the engine is drowning, and the excess is making it into the oil which will thin it out and lower your pressure.
 
AJ/FormS said:
in this case; .8 second is 10%. That seems like a lot.
Is that 360 a regular LA engine?
You call it a flutter but talk as if it's just drifting........ I mean I have no clue, but just want to get my thinking straight. Just curious; what is the idle speed?
Click to expand...
Yes, 360LA engine. As far as the guage, it looks like a vacuum guage with a valve issue. It rapidly sweeps between 50-55 psi at idle, which is 1100 rpm in park. If I bring the Rpm's up to about 1800, it will get steady and reach around 60psi.
 
You must log in or register to reply here.
-

Back
Top