Low oil pressure after oil filter change:

My 340 had about three-four hours of cruising time after the cam break in, so it was time to dump the break in oil and filter. I changed them both (was a Napa Gold filter/Driven Break In oil to another Napa Gold filter/Driven 10-W30 High Zinc) and went on a test drive. The oil pressure was fine before leaving the garage (22’ish at warm idle and 50’ish at cruise) but after a few WOT downshifts, I noticed that the oil pressure at cruise was down to 25’ish. So, I drove it back to the garage while listening and being careful, but I did not hear any extra noises (solid cam) coming from the engine.

Once the engine cooled off the next day, I checked out the wires on the Holley fuel pump safety switch and found a loose wire. So, I snugged it back up and thought that I found the problem. I then started the car back up to find that the oil pressure was at 25’ish again at high idle which is low. I was waiting on the engine to warm up and checking for leaks (just replaced the speedo cable seal) and then I was under the hood, and I noticed my fuel pressure gauge was starting to jump around (this pressure is usually solid). After a few seconds of watching it, it was dropping fast, and I was waiting on the engine to die. Once the engine died, I shut off the ignition and started thinking about what is now causing the low oil pressure and the low fuel pressure? I have a manual prime button for the electric fuel pump, so I pressed it for a few seconds and my fuel bowls filled up like normal. So, the fuel pump works while using the manual push button, but it is not working now while the engine is running.

I decided to replace the Holley safety switch since it drives the fuel pump. While doing so, I pulled the pipe/adapter setup that I have on the back of the engine that mounts the oil pressure sensor and this safety switch. I cleaned up the pipe/adapter (nothing inside that would cause a low oil pressure reading) and remounted the oil pressure sensor and the safety switch. But now I am thinking out loud that neither one of these would make the oil pressure read low, but the switch does shut off the fuel pump if the pressure is too low. It did not lose all oil pressure, but now I am getting half of what I am used to seeing on the oil pressure gauge.

So now I am thinking of replacing the oil filter (I have a new Wix filter) since it was the only change to the engine before I made the next drive as when it started to lose oil pressure. I will change this filter this weekend and then see what the oil pressure is at startup.

But if changing the oil filter gives me the same oil pressure result, what are my next few steps? Pull the dist/oil pump drive shaft and inspect? Then plan on pulling the oil pan to replace the pump/pickup?

What do you think? I used a well known/good filter brand before and after the cam break in.


Thank you.

Keep it simple sam, change the filter & go from there. there are defective parts

My first step in resolving low oil pressure problems is to swap in a different mechanical gauge.

Cut open the old and new filter to look for metal filings.

There was a common trick to block off oil galleries on Roller and sometimes mechanical cams. Was this done?

If all checks out then pull the pan and double check that the pump isn't chewed up, the pickup tube is tight and free of garbage. Make sure the relief valve is free to move correctly.

If all that checks out then check the crank and bearings for wear while the pan is off.

Hope it helps.

Thank you for the responses!
I will stay the course and see what happens with the new filter.

napa gold is made by wix. i used a napa gold on my 91 318 truck. after it set all night and 1st start of day, lifters rattled a little. went to mopar 090 and no more rattle on cold start.

try a different filter first but not another wix/napa. fuel pressure issue? are you trying to use a mechanical pump to pull thru a vane type electric pump?

Holler how it turns out

""fuel pressure issue? are you trying to use a mechanical pump to pull thru a vane type electric pump?""

I am using an electric pump only. The fuel pressure issue is due to the oil pressure switch doing its job due to the low oil pressure. Once I get the low oil pressure resolved, the fuel pressure should be back.

I swapped out the oil filter last night but then I did ran out of time, so I will start it up Saturday to see what the oil pressure reads.

Thanks everyone!

If it still has low oil pressure you probably have a stuck high pressure bypass valve in the oil pump
Been there, done that more than once on a new motor during breakin

25 psi at idle is NOT LOW. OE spec is like 7-9 psi. I'm betting bypass valve.

Had a neighbor lose oil pressure and pick up a rock knock after changing the oil in his new to him 58 Powerwagon.

Turns out the guy he bought it from used gear oil in it to hide the rod knock in order to sell it.

Did you change oil weights or brands per chance?

I changed from the Driven break in oil to the Lucas Hot Rod 10W-40.

Having used neither oil, I can't comment on brands.

What weight was your break in oil?

you put a new cam and lifters in?
maybe the new lifters have slightly more clearance in the bores than the old?

""What weight was your break in oil?""
- It was the Driven brand 30.



""you put a new cam and lifters in?
maybe the new lifters have slightly more clearance in the bores than the old?""

My previous cam was in this engine for 16 years and it always showed 22'ish at idle and 50'ish at cruise. Then I swapped the cam/lifters and it too showed the same oil pressure during break in and the next 3-4 hours of driving. Then right after I drained the break in oil/filter and replaced them both is when the oil pressure went down on the first drive.

Thank you both!

Just check or replace in the order of simplest to hardest. Probably:

1) Filter
2) guage/send.
3) Pull valve covers
4) drop pan

Cut open the just replaced oil filter too

Thank you BSB67. I was just thinking if I have a mechanical gauge that I could swap into the existing sender port. 👍

Note: I forgot to mention this but I already cut open the 1 drive NAPA/Wix oil filter and did not find any metal shavings in the filter material. The new filter is a WIX brand.

Myself, I would
1. Put a drill motor on the oil pump drive. Take a reading. The advantage to doing so is you now have a constant RPM on the pump to take and compare readings. In addition, if there is a problem no further damage is being done by starting the motor.
A Corded electric drill would be preferred as you are removing the variable of a cordless drills battery. Yes I still have 3 or so LOL

2. Then install a new or known good mechanical gauge and repeat.
3. Compare the two.
4.Only other variable is the oils which you could change again if desired but a pricey option
5. Pulling the valve covers is easier that the pan but if # 4 doesn't revive the pressure see #6. If you do pull the covers make sure the ends of the rocker shafts are not leaking (longshot)

6. I going to agree with a few others and guess that the relief valve in the oil pump is hung slightly open or the pickup tube developed and issue.
The good new is no metal in the filter keep us posted

I once had a 318 that developed low pressure and it was the threaded galley plug behind the cam gear.

UPDATE:

I fired it up and the oil pressure went to 38-40psi cold High Idle (which is normal on this gauge) and after about 10 minutes of fast idle, it worked its way downward. At an idle of 1200rpms, the oil pressure looks like 12-13psi which is also what I would call normal on this guage. It appears that I am back to what I would call normal oil psi readings for this car.

Issues:
The main issue that I found while swapping out the Holley fuel pump safety switch was that when I tightened down the three screws on top of the switch, they were tight. But what I found by mistake was that the screws were tight, but the wire ferrules were not! So I added a washer to two of the three screws and the wire ferrules are now tight.

I mentioned earlier that when I first noticed my oil pressure went down after that first drive after the oil change, I noticed when I got back to the garage that one of the three screws had come loose on the previous FPSS. So I tightened it up but there was no change in the oil pressure. When I swapped over to the new FPSS, that is when I found that the screws were not tightening down on the ferrules even though the screws were tight. I now have a backup FPSS

My fuel pressure is now back to normal too. One of the wires on the FPSS goes to the fuel pump.

Awesome glad it wasn't internal.