Oil pressure drops when warmed up

[harveyspoint]

I have a 1947 Plymouth Coupe with '51 Overdrive and '53 engine...When started cold, oil pressure is always 40#..

As it warms up, it gradually goes down to 20# pressure.    No extra noise....Always starts with no more than

2 - 3 turns....It also has a split exhaust manifold.....Runs down the road like a modern car...Any ideas?....Thanks....

[Ajgkirkwood]

That is normal, your oil is thicker hen it's cold. If it goes to 40+ psi while your cruising, your very good. My motor when cold is 20, warm drops to like 7.... when cruise its 20-25....... 

[Sharps40]

10 psi per thousand rpm is pretty much the gold standard/recommendation.   5 psi idling warm is the low end.  (Most modern engines shut down below 5 psi at warm idle to save the bearings/engine).

[Worden18]

My 51 Dodge does the same thing; on a rebuilt engine.  No worries ?

[bluefoxamazone]

I use a 20/50 multigrade oil and my needle does not move a bit away from 40 or slightly higher. Not if I am idling nor if I am running at 100km/hr.

[John Reddie]

When I had my P15's and my '48 Dodge back in the late '50's and early '60's, they were pretty well used and had tired engines. I'd get 40 pounds oil pressure at cruising speed and 0 at idle. If I coasted down a steep hill, it would blow out some noticeable smoke too. I used to buy oil in glass bottles with a tin cone on the top for pouring it at a local salvage yard.; 2 quarts for a quarter if you put it in yourself. I drove the cars respectively and got pretty good service from them for the most part. We had very little money then but a lot of fun and now fond memories.

John R

[Don Coatney]

The P-15 I drove in high school had the not so rare 5 cylinder engine. Zero oil pressure at idle and 10 pounds at speed. I loaded it up with STP to get this much oil pressure. I also used the glass jugs of recycled oil at 10 cents per jug.

[PT81Jan]

5 hours ago, bluefoxamazone said:

I use a 20/50 multigrade oil and my needle does not move a bit away from 40 or slightly higher. Not if I am idling nor if I am running at 100km/hr.

 

I guess your temp gauge pointer is stuck at 40 and you should apply a drop of oil to it !?

No, just joking  ... sounds like you have a really healthy engine there ! ?

Edited April 8, 2019 by PT81Jan

[John Reddie]

3 hours ago, Don Coatney said:

The P-15 I drove in high school had the not so rare 5 cylinder engine. Zero oil pressure at idle and 10 pounds at speed. I loaded it up with STP to get this much oil pressure. I also used the glass jugs of recycled oil at 10 cents per jug.

 You got a better deal than I did at 10 cents a bottle. I never thought to put in STP. I could have probably got the pressure up to 3 or 4 pounds at idle?.  I had two friends that had P15's with engines about as tired as mine was. One guy punched a connecting rod through the side of the block and the other ended up spinning a rod bearing. The didn't heed my advice and drove their cars hard. A little respect went a good distance with those old gems.

John R

[plymouthcranbrook]

6 hours ago, Don Coatney said:

The P-15 I drove in high school had the not so rare 5 cylinder engine. Zero oil pressure at idle and 10 pounds at speed. I loaded it up with STP to get this much oil pressure. I also used the glass jugs of recycled oil at 10 cents per jug.

Apparently the 5 cylinder engine is not as rare as you suppose. My 54 Savoy in high school also had 0 oil pressure except when I would downshift at about 30 mph into 2nd gear. Then i had 50 psi for a short while. In this case number 5 had a bad rod bearing and I had 0 money to do anything about it except pull the pan on the 3 occasions when it locked up tight and slid to a stop on the street. Friends used to push it home with their cars and I would take it apart. Finally gave up when the clutch went out and off to the junkyard it went. Got $4.00 for it and half went to the friend who pulled it out there. I also ran a combination of straight STP and Rislone