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73Runner4spd
11-13-2012, 01:41 PM
Looking for possible culprits in my loss of oil pressure. Its a 400 big block that I run 20w 50 in. Until recently it always held around 60-65 psi cold and when warm it would drop to around 45 psi at idle. It would also go up around 10 psi per 1k rpm Seemed great. Recently at cold idle it stays around 40 psi and warm it drops to 15 to 20 psi sometimes down to 0, when this happens it struggles to stay running. It also no longer goes up 10 psi per 1k rpm, now it goes all over the place but will not go above 40 psi. It will go up to maybe 40 and drop even under power. I don't know if its the pump, a spit out lifter, or what. Just looking for other possibilities and if anyone has ever seen this behavior before, Thanks guys

rusty duster
11-13-2012, 05:50 PM
check the oil pump pressure releaf plunger,might be sticking.

440roadrunner
11-13-2012, 06:45 PM
My gosh you oughta be able to tell if a lifter is "out" by the way it runs.

pressure relief, or PULL THE PUMP and suspect the O ring around the stem of the pump where it enters the engine.

JVMopar
11-13-2012, 10:31 PM
I had a filter cause low oil pressure. If it were mine I'd try a different filter.

John Kunkel
11-14-2012, 02:30 PM
it stays around 40 psi and warm it drops to 15 to 20 psi sometimes down to 0, when this happens it struggles to stay running.

All of the possibilities so far don't explain the "struggles to stay running" part....mystifying.

Dart14
11-14-2012, 03:22 PM
check the oil pick up in the pan for blockage. i once had a 440 that was clogged with plastic type pieces that came off one of the timing chain gears. It would idle erraticley at times.

JVMopar
11-14-2012, 11:03 PM
An electrical problem could cause both a running problem and the gauge to read erratic.

chirorod
11-16-2012, 08:06 AM
First thing is to get an accurate reading of oil pressure. Put a mechanical gauge on it. If oil pressure is actually low, then all previous suggestions are possibilities. In addition, worn bearings can cause low pressure. But the struggling to stay running symptom makes it sound like pressure is low and something is seizing up.

73Runner4spd
11-16-2012, 09:19 PM
An electrical problem could cause both a running problem and the gauge to read erratic.

Its a mechanical gauge, but I do have a feeling the running problem is an electrical problem

chirorod
11-17-2012, 08:28 AM
I should have said to use a gauge out of your tool box to check pressure. That way, if something is wrong with the gauge system in the car, you by-pass that. I haven't had to use mine all that often, but I have had one in my tool box for about 50 years. It got borrowed often when I was in a shop. It sure helps to narrow things down. Oil pressure is serious business, like heart problems.

73Runner4spd
11-18-2012, 01:05 PM
I should have said to use a gauge out of your tool box to check pressure. That way, if something is wrong with the gauge system in the car, you by-pass that. I haven't had to use mine all that often, but I have had one in my tool box for about 50 years. It got borrowed often when I was in a shop. It sure helps to narrow things down. Oil pressure is serious business, like heart problems.

Ill def look into that, in the mean time I replaced the mobil one filter with a mopar filter and put some more non synthetic 20 50 in it and boom held 75 cold at idle and 40 warm at idle, no more erratic oil pressure. Just took it out for a spin maybe 10 miles when I came to a stop it dropped back down to 20 while in gear with the clutch in. Pop it in neutral and back up to 40. However it does go up as it should under power.

440roadrunner
11-18-2012, 01:59 PM
The FILTER should not affect oil pressure, unless you just plain have the incorrect filter. DO NOT use Fram filters. One of the most commonly available filters which are good quality is Wix, who also makes NAPA filters. You can get Wix at NAPA or O'Reallys auto parts.. Do you have a mechanical fuel pump? I'm wondering if you have fuel dilution of hte oil?

73Runner4spd
11-18-2012, 02:23 PM
Yes its mechanical

70Ted
11-19-2012, 06:31 PM
sounds like woren main and or rod bearings