Oil Pressure

1

1950MercMan

Junior Member
Looking for some input on a possible oil pressure issue.
I have a 1950 Mercury with the 255 flathead engine. I took it out for a drive yesterday, and while sitting at idle in traffic at a red signal, I noticed that the oil pressure gauge was nearly at zero. I immediately returned home and I noticed that under acceleration the pressure was about at the middle of the gauge around 30.
The next morning I went out to the garage and started it up. The pressure immediately went to about 30 and stayed there. I continued to allow the engine to run. As it reached operating temp I revved the engine some and the pressure remained at 30, but as I allowed it to idle the pressure went down to app. 15.
The original owner's manual states that the oil pressure should register around 50 except when at idle - I have never seen it above 30. This is all assuming that the gauge is working correctly.
Can anyone shed any light as to what the proper oil pressure should be reading both at operating acceleration, and at idle. Is this normally do I possible have a faulty gauge or oil pump?
 
(1) hook up good quality mechanical oil pressure gauge
(2) oil change (many use 20/50 weight) I do
(3) "tired" engine
 
Perhaps a weak or defective relief spring in the pump. This would open early, lowering maximum pressure below specs. It wouldn't have any effect on the low pressure at idle though.

My choice is (3.) above.
 
I have had this problem a number times with Flat Head engines and a few OHV engines.
I have found 2 different problems at different times.

1. The bypass plunger in the pump was stuck at say 30# when cold or engine revved up. and about 5# at normal warm up temp.
2. The oil pressure sender was faulty.

On the first problem I cleaned the plunger and the plunger bore of crud and oil pressure
went to 50# +, cold, or revved at norm temp. 15 to 20# @ idle norm temp.
On the second problem, changed the sender. Problem solved.

Also if the pump is weak you can use a stronger bypass spring.
 
This will be my last question no answers in my life time. Question what is half of 80?
Question 2; why is 30 half of 80? on King Seely gauges?

As Gene said a good 0 to 80 mechanical gauge I have bought car that way" It says 60# all day all night and the dash says 30# hot idle and mechanical says 40# so 30 has to be a Factory misprint on the face plate? yes / no. Now hard to believe last year my dash gauge drifted to like 10# (Steward Warner says 60#) Got new sender from Joe's same thing. Then in my stash a oil gauge from a Truck F Series on fender with jumper wires (its 6volt) start it and this gauge goes way past 30#. So i found a new Ford stock in box & mine is special it has Red Super Deluxe markings. I wait awhile till my boy is free no way my bones can get under there. OK done now dash gauge goes up like 3/4 that's about 60#.. Put on ya seatbealts; my findings with my original gauge = Spider webs so small I needed a spyglass HOW? = very true story...a nano spider? probably a dash light fell out yrs ago. sam
 
I thank everyone for the input.
I am going to hook up a mechanical gauge and see what the readings are, and go from there. Seems like a good starting point.
 
Just an update.
I hooked up a mechanical gauge. Upon reaching operating temp and under acceleration the pressure read between 40 and 45 psi. At idle, it rested between 20-23; never went below 20.
So, I think I am OK. I am going to also change over to 10W-40, and that may boost it a little more.

Thanks again.
 
Flatheads are more about volume than pressure. When mine is hot and idling on a hot summer day it's around 10 psi which is OK.
 
flathead4rd said:
Flatheads are more about volume than pressure. When mine is hot and idling on a hot summer day it's around 10 psi which is OK.
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YEP! - This, from Ron Bishop's book "Rebuilding The Famous Ford Flathead" - Page 51 - "Ford used 40 non-detergent oil (Summer) in all of the flathead motors. The flathead oil system ran between 10-15 pounds of pressure, but is not considered a pressurized system by today's standards."- This for factory stock engines....
 
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flathead4rd said:
Flatheads are more about volume than pressure. When mine is hot and idling on a hot summer day it's around 10 psi which is OK.
Click to expand...

This is correct; if you are in this range, going to a thicker oil is not a good idea. I run 10-30 in all of my cars (none are worn out). If your engine is marginal, going to a higher weight oil may be OK.
 
Okay.

I have had this car less than a year. The engine seems strong with good power and acceleration. Throws no smoke at all.
Thanks for the input on oil weight. With that, I will stay with 10-30. This is my first flathead, so I really appreciate all the info.
 
I should have qualified my remarks.
My engine was rebuilt in 1987
When we lived in the northwest I absolutely ran 10w40 and still would if we were still there.
Now that we live outside Las Vegas my car spends hours running 2500-2600 rpms in 100-105 * heat.
The flathead was originally designed to run [straight grade] 40 weight in the summer months.
Running 20w50 under those conditions in a motor that is 30+ years old makes just good sense (to me)
 
Gene, just out of curiosity do you run an auxiliary push electric fan w the mechanical one to help cool on those 100 degree plus days?:eek:
 
I was just looking through the original owner's manual for the 1950 Merc.
It recommends using SAE 20 for warm weather. I am not going to do that, of course; I just found it curious.
 
AnthonyG said:
Gene, just out of curiosity do you run an auxiliary push electric fan w the mechanical one to help cool on those 100 degree plus days?:eek:
Click to expand...

Pitched the mechanical years ago. I'm using a 2 speed late '90s SVO and shroud. Practically a bolt on made for the old shoebox. 2 fan switches in bottom of tank 185 and 195. using a 70s Volvo controller (relays and circuit breakers)

Radiator is 3 core 5/8" tube and 15 fins per inch. Radiator mechanic made me a believer (water stays exposed to fins longer and more fins per inch than a conventional 4 core). It's a balance between airflow and water staying in radiator longer.

Ignition is Chebby (mechanical is 18* @ 1800 rpms for a total of 22@ 2200/thanks Bubba) with the vacuum advance running off manifold (14* @ 15"). Stoplight to stoplight cooling is so much better than ported.
 
Sounds great Gene! Im in NE Pa. running a modified 8BA, along with the mech. fan I put a electric push fan in front of radiator for the annoying “ Stoplight to stoplight cooling issues in Summer”
 
My Lincoln/Mercury O/H manual that covers 1949 thru 1951 calls out lower viscosities than SAE 20 for extreme cold such as SAE 10 for extended temps below freezing and SAE 5 for temps down to -10 degrees F. SAE 20W20 was what we used till it was in summertime temps of over 100 degrees F when we switched to SAE 30. It stays hot in Kansas for quite a few months so that was the the common practice on the farm until SAE 10W40 basically replaced SAE 30. Now days it's getting harder to find SAE 10W40 but SAE 10W30 is fine for these old motors unless the bottom end bearings are getting a bit too much on the loose side.
 
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