Oil Pressure Readings Down

[racertb]

Hey All:

Took the old gal out on a 55 mile round trip this past weekend, the first time I've had her out more than a few miles in the last two years.  Although she ran great, the oil pressure started dropping after about 20 miles into the trip.  To make a long story short, for most of the time the pressure was reading very close to the same as my mph, i.e., 40lbs. at 40mph, 30lbs. at 30 mph, etc.  In the past, the pressure while driving would be about 40lbs. +/- at all speeds (except idle).

The more alarming part was at idle pressure.  In the past, about 20lbs. minimum when hot at a stop light or stopped wherever.  This time, the pressure dipped as low as 14lbs. at several stops, which I never saw before.  At a traffic light close to home on the return trip, she was idling at about 14lbs and seemed like she might stall and the pressure looked like it was starting to slighly dip some more.  Since there was no one around and the light wasn't changing, I took off so I could keep moving and get the pressure back up.  I made it safely home and ended up changing the oil, which I wanted to do a couple weeks ago.  Afterward, she started fine and I let her run for a few minutes.

I cleaned the screen in the pan 2-3 years ago and it was clean then and since I haven't been driving the car, I doubt the screen is the issue.

I'm going to check for any loose oil lines, but I haven't done anything with them to think that may be an issue.  Maybe the pump needs to be rebuilt?  For what it's worth, I run 10w-30 and that's what the car has used since the mid-80's.

Anything else I should check out?

Thanks!

Ted

[Des28Qau]

Hi , I was interested to here other replies but as there is none yet here is my positive reply.
Remember that an oil pump is a positive displacement pump, and the pressure is only achived due to the resistance to flow.
Basicly the oil pressure will increase with RPM to the set point of the relief valve.
As oil gets hot it thins and flows more easily through passages and bearings etc, resulting in lower pressure but increased flow.
( good oil flow is essential for cooling the bearings etc )
It will take 20+miles for the oil to get up to 200 degrees +,
You mention that at the trafic lights, the engine was about to stall when your low oil presure was the greatest concern,
maybe it was just due to low rpm and hot oil ?
Perhaps and hopfully next time you take the old gal out for your just a few miles drive all may be normal.
Regards Des.

[frankp]

Ted,  Nothing comes to mind beyond what you suggested.  Did your old oil look thin/diluted when you changed it?  Des gave a good explanation of how system works.   frank

[racertb]

Thanks Des...I agree with you on the low RPM near the end of the trip.  I was just a little concerned that my pressure has always been a little higher and never got down to 14lbs. at idle at anytime.  Like I stated, I did an oil change anyway (needed it) so we'll see what happens.

Frank - I changed the oil after the trip since the car wasn't driven since it had been down for a while with the timing issues.  There wasn't many miles on the oil, but it was in there for a couple years.  It looked like it always looked, not crud but not thin (to me).  I've always used 10w-30 (and before my Dad did as well after the motor was rebuilt in the '80's).  No no prior issues with the oil/pressure.

Regardless of the pressure, the car ran great!

Ted

[rwollman]

was wondering if you are using the vacuum fuel pump? If you have a small vacuum leak could affect oil pressure especially at idle as vacuum is supplied by oil pump....Just food for thought. 

[racertb]

That makes sense with the vacuum tank/pump, but I'm using an electric pump.  I'm going to see how it goes this weekend.

[racertb]

Things much better after oil change this weekend...take a look:

Idling hot

http://vid947.photobucket.com/albums/ad320/racertb/Car%20Stuff/20151017_140939_zpswrk0kkdc.mp4

Cruising 1

http://vid947.photobucket.com/albums/ad320/racertb/Car%20Stuff/20151017_140442_zpshpwtaekg.mp4

Cruising 2

http://vid947.photobucket.com/albums/ad320/racertb/Car%20Stuff/20151017_135827_zpsslrgjrlo.mp4

[ski]

Nice!

[29plycoop]

Thanks for the ride. Nice car!

[frankp]

Just like being in the passenger seat.  Thanks for the ride.

[chetbrz]

Your car is looking good and running great. 

Congratulations,  Chet...

[racertb]

Thanks everyone.  Keeping my fingers crossed!

[imoore]

Just a little query. To what extent was the engine rebuilt to. I dont want to be that person. But listening to the engine on your third video. Makes me concerned about the bearings. I only ask this cause my 28 sounds very similar which has been confirmed with slightly worn bigends.
But also maybe its just how they sound.
Here is a link to mine going up a long Hill. Its very noticably louder.
Like I said just what it sounds like through my speaker.
https://youtu.be/DgMsAVbrQrk
I could very well be wrong
Ian

[racertb]

The phone recording makes it sound rough.  It really sounds good and runs smooth in person.  There is an occasional buzzing/rattling at some rpms due to the throttle linkage next to the firewall.   I don't notice anything else.  Motor was redone in the '80's.

[racertb]

I can't play your video.