Flathead Engine Oil Pressure ?

[38 coupe]

With all due respect to other people's opinions here, flow is not all you need in plain bearings. The oil does more than just lubricate, it prevents metal to metal contact. The pressure of the oil in the main and rod bearings has to be greater than the pressure downward on the applicable bearing. Radial force goes up with the square of the velocity so you need much more pressure at higher r.p.m. than you do at idle. Ford calculated the average pressure on the bearings at the highest expected r.p.m. and set the bypass valve to just above that pressure. As the power went up in the flatheads, so did the bypass valve pressure.

That said, I do not worry when my 37 has 10 lbs or less at idle.

[flatjack9]

Actually, metal to metal contact does not occur because the load is supported by the pressure created in the lubricant by the relative motion of the shaft and the bearing and by the viscosity of the oil. As the speed increases this "pumping" action also increases, supporting the increased load.

[G.M.]

I think were are getting in never, never land with to many I thinks and guess'. I believe we all kind of agreed almost any oil will work in these engines. Take your pick. But I believe in 15 lbs idle and 40 driving. Whether this reduces wear in 150,000 miles is the question. I THINK it will. I only have 110,000 miles on the 39 so it will be a while. G.M.

[41ford1]

GM posted something a while back that it usually is a simple thing to correct low oil pressure. He mentioned shimming the relief valve in the valve chest. While I had the manifold off I tried it. With the spring shimmed by .070" (2 washers) my hot oil pressure went from 18-20PSI to 40-45PSI at 50MPH. Idle oil pressure went from about 4 to 15PSI. It really was as simple as GM said. Thank you sir!

[FlatheadTed]

Part of the function of the relief valve is to open when cold to give a spray of oil over the top of the cam gear ,this lubes it and the thrust face , and the rear dizzy bush ,

[Newc]

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Hi all; Remember that the 'early engines have their relief in the lifter valley, and the late pumps have the 'built in' relief on the pump. You have to adj the valley relief or it will dump your new pump's higher pressure. correct? later Newc

[G.M.]

Correct and you can put 3/16 to 1/4 inch shim in the valley valve so it don't open if a later pump with the valve is installed. The valley valve don't have to open to lube the timing gears etc. The valley valve has a flat spot on the seat so it always leaks enough oil on the gears. G.M.

[john mullen]

I changed my oil to 10/30hd. and about 200 miles later it starts to knock .I puled it out only to find that the 10/30hd cut the sludge in the engine and cloged the picup screen and killed the engine. so beware stay with what was in the engine before you got it if u can find what the other owner used .I found out fron the former owner he used 30w non detergent A lesson welled learned....

[ford1]

before you do alot of in necessary work, ford does not give an oil pressure figure at idle, they say #35 at 35 mph, most of all the engines i have worked on will read #5 at hot idle, which is normal, oil flow to moving parts is more important than pressure, i would rather have 5 gallons a minute to all moving parts than 3 drops per minute to the moving parts at #100 pressure, if the engine runs good and doesnt leak oil leave it alone, disturb any thing i will bet you will have an oil leak some where when your done, thats murphys law

[Ol' Ron]

Ford1 has the answer, saves me from comenting.

[Binx]

Totally agree ford1. 10 psi per 1000 rpm is the "gold standard" of SAE. And yes, it is about flow -- not pressure.

Lonnie

[Old Henry]

Originally Posted by ford1

before you do alot of in necessary work, ford does not give an oil pressure figure at idle, they say #35 at 35 mph, most of all the engines i have worked on will read #5 at hot idle, which is normal, oil flow to moving parts is more important than pressure, i would rather have 5 gallons a minute to all moving parts than 3 drops per minute to the moving parts at #100 pressure, if the engine runs good and doesnt leak oil leave it alone, disturb any thing i will bet you will have an oil leak some where when your done, thats murphys law

Originally Posted by Ol' Ron

Ford1 has the answer, saves me from comenting.

Originally Posted by Binx

Totally agree ford1. 10 psi per 1000 rpm is the "gold standard" of SAE. And yes, it is about flow -- not pressure.

Lonnie

Amen. And amen.

[Bassman/NZ]

So just add chaos to confusion, or is it confusion to chaos? It would seem then that the oil pressure gauge is pretty much redundant......

[flatjack9]

Put a piece of tape over it.

[46ford]

Originally Posted by 41ford1

GM posted something a while back that it usually is a simple thing to correct low oil pressure. He mentioned shimming the relief valve in the valve chest. While I had the manifold off I tried it. With the spring shimmed by .070" (2 washers) my hot oil pressure went from 18-20PSI to 40-45PSI at 50MPH. Idle oil pressure went from about 4 to 15PSI. It really was as simple as GM said. Thank you sir!

Does this really increase engine oil pressure throughout or just show a higher number on the gauge? Anyone got a pic of this? Mine doesn't make any noise but drops into the single digits hot at idle.

[41ford1]

It does increase the pressure in the system. The relief valve in pre '49 is at the front end of the main oil line. The oil pump is at the rear. The attached pic shows the oil line. It is the pipe running down the center of the valve chest. The relief is just below the front edge of the valve chest opening. The relief cover is 15/16" hex. Unscrew that to expose the spring and valve. The shim goes in the spring recess in the cover. Use grease to hold it there for reassembly.

[ora masters]

Originally Posted by Mike in Louisiana

Thanks for everyones info I plan on taking the oil pan off and cleaning it along with checking the oil pump and oil pump screen. So far I don't have any engine oil leaks. I'm also going to try the Delo 15-40 which I have used in my Dirt moving tractors for almost 20 years and they are up to 660 HP now.

Thanks

Mike

my gauge does not work so i dont have to put tape over it

[Ol' Ron]

If you don't trust your gauge, there is a test that work quit well, but is kinda messy. Warm up the engine, remove the plug/sending unit on side of block. start engine if oil just dribbles out you have a problem. If it shoots out a coupla feet, your good to go.

[Old Henry]

Or, you can do this. It's less messy and more accurate.

Get a cheap mechanical gauge such as this one from AutoZone for $18.00 here: http://www.autozone.com/autozone/acc...ier=267574_0_0_:

And temporarily screw it in place of your oil sender:


Run the tube up the firewall


And under the hood. Then hang it on the windeshield wiper temporarily


And read it through the windshield while driving around to see what the real pressure is cold to hot, stopped to high speed.

[41ford1]

Prof. Henry, That is the same gauge I use to verify the stock one. Did it the same way you did.
Ol'Ron, I used your method when I first got the truck while trying to figure out why there was zero pressure indicated after warm up. At warm idle there was more than trickle a lot less strong stream. Get this. A previous owner installed a pressure switch in place of the sender. Wired that in series with a resistor to put the gauge mid scale (about 30#) when there was enough pressure to close the switch. The switch closed at 8PSI. So eventually after warm up the idle pressure dropped to something less than 8PSI. Therefore 0PSI indicated.
As an FYI the Ford manuals refer to what I am calling an oil pressure relief valve as an oil pressure REGULATOR.