1950 218 oil pump low pressure

[Wayne Deluxe]

Started a new project 1950 Plymouth deluxe with the 218 in it. 

The engine runs well, how ever once warmed and bin driving for a while, at idle it shows very little oil pressure, while driving it has 40 psi. 

My question is, should I be concerned about the low pressure at idle? 

[1949 Wraith]

What do you consider very low oil pressure? I think the 218 in my '42 Fargo book lists 15 PSI at idle. you might consider running something like Rotella 15-40 which will probably bring it up a bit.

[greg g]

I believe the manual says any positive  pressure at warm idle is acceptable. Then it recommends 10 psi per 10mph to a max of 50 psi.  My 56 230 rebuild has 45K, cold start is just over 50 at idle, dropping to 40 at hot idle, and 45 at hot cruise.  The original 218 with 75k miles started at 35, dropped to 15 hot idle and went down the road at 30/35.  Currently  running 15w40 rotella in the rebuild, straight 30 was run in the old engine.  I can tell when it needs an add of oil as the needle will drop to 20 going around turns or under wide open acceleration then it returns to normal as it levels in the pan.

[chrysler1941]

28 minutes ago, greg g said:

cold start is just over 50 at idle

Is it a full flow system? If bypass, it's too high. It could damage the gauge. Have you checked your oil pressure relief valve? Uncle Tech says 40-45 it should open

You may have wrong spring

[kencombs]

Low to me is 5-15PSI at idle,  and I'd be ok with 10, maybe not 5, as long as increasing RPM brings it up quickly. 

 

If the bearing condition is unknown, it may be worthwhile to pull the pan and check the rods and mains.  But, for me that always opens a huge can of worms.  You know, as long as I'm in here let's...

 

If it is an older tired engine, consider a heavier multi-weight oil as mentioned earlier.  15w40 or so.

 

So my final answer, Maybe.  No help I know, but that's the best I got.

[greg g]

3 hours ago, chrysler1941 said:

Is it a full flow system? If bypass, it's too high. It could damage the gauge. Have you checked your oil pressure relief valve? Uncle Tech says 40-45 it should open

You may have wrong spring

It's only at 50 for a few seconds then it drops to 40. It's a bypass system.

Edited April 24, 2021 by greg g

[chrysler1941]

11 hours ago, greg g said:

It's only at 50 for a few seconds then it drops to 40. It's a bypass system.

What oil are you running?

[jpwuertz]

I have a B3B with a 218 and have been running 30 wt non detergent oil in it.  Would there be a problem if I switched to Rotella 15-40.  I assume the Rotella would give the engine better wear protection than the 30wt that I currently use..

[chrysler1941]

25 minutes ago, jpwuertz said:

I have a B3B with a 218 and have been running 30 wt non detergent oil in it.  Would there be a problem if I switched to Rotella 15-40.  I assume the Rotella would give the engine better wear protection than the 30wt that I currently use..

There are so many opinions about engine oil. It's almost a religion. ? A subject I wont get into. I will only comment regarding my engine.

 

Choosing the right oil is all about engine wear during cold start and warm up.

 

My Chrysler flathead was designed with tolerance for SAE 30W. I will never use multi grade oils.

Simple reason, a 15-40 is 15 when cold and changes to 40 when warm. When cold cranking, 15W is half of what's needed and will not lubricate enough. When warm it's 40 and too thick. It will show nice pressure reading, but how's the engine doing? When hot all, oils are the same.  Then there's the floating pick up tube. It has a purpose I will not get into.

 

There is an interesting 33 page documentation about oil lubrication in engines. It's mostly for flat tappet OHV engines but there is some surprising info. You can download it here.

Selection of the right oil for flat tappet engines.pdf

[greg g]

On 4/25/2021 at 3:09 AM, chrysler1941 said:

What oil are you running?

Currently I am running 15w40 from shell.  This after a rebuild 45k miles ago. My first fill was straight 30 detergent for break in. I then used 15w40 traveller all fleet oil from tractor supply.  When I decided to have the oil changed at a shop, instead of DYI, he had the Rotella 15w40 in-stock so thats what's been used for the past 4 or 5 years. I usually put about 5000 to 6000 miles on the car but it's not driven in below freezing weather so the W part of the viscosity issue doesn't come into play.

 As for the theology of oil goes I don't  believe in deviating from the book for engines of unknown history. That is if you know not what's been in it, follow the makers gospel.  I also believe any oil available today is superior to what was available when the car was created.  But detergents in an old motor of questionable prior behavior is problematic because loosened dirt can cause more trouble than undisturbed dirt.

 

And when all else has been tried the following cocktail may be beneficial if one takes a leap of faith

 

1 qt SAE 30 NON DETERGENT to follow the gospel

1 qt 10W30 as there is no doubt there has been some perversion in the past

1qt of high mileage engine oil because its got lots miles

1qt SAE 50 because old cars need thicker oil

1 pint of Marvel Mystery oil because it's a Mystery of faith

1 pint of STP for the zinc

1 pint of choose one, Rislone,Wynns Friction Proof or Bahrdall. to honor the snake oil purveyors.

 

May the blessings of hydrocarbons, surfactants, and friction reducers be with you.

 

 

 

Edited April 27, 2021 by greg g

[1949 Wraith]

Another point to consider. If your engine has been run on non detergent oil for a long time there will be a build up of sludge in the oil pan. you will want to clean the engine of the sludge before you change to a modern multi weight detergent oil.