Flathead Engine Oil Pressure ?

[Mike in Louisiana]

When starting my 1936 1.5 ton truck with the 59A B engine being cool I have 60 PSI engine oil pressure on my new after market oil pressure gage and a little over 50 at low idle on the factory gauge for about 5 minutes then as the oil warms up it starts slowly coming down and after about 15 minutes of driving the truck down the highway I have 18 PSI at HI idle and 2 PSI at low idle. I left it over night and it does same thing the next day. The engine runs real smooth and doesn't smoke at all. I'm using 30wt non detergent oil.

The truck has not been started since 1972. I changed oil but did not remove oil pan to clean.

What is the normal Hi idle and Low idle oil pressure for this engine?

What may be the reason of the oil pressure coming down after warm up?

Thanks

Mike

[tierod]

Warm oil is thinner thus the lower indicated pressure.

[38 coupe]

"Normal" varies a bit on flathead, particularly depending on the oil pump type, oil used, wear in bearings, etc.

I think you will find you have much better hot oil pressure if you switch to a 15W-40 diesel oil like Rotella-T or Delo 400.

[Mike in Louisiana]

I use Delo 15-40 in my tractors. I understand warm oil is thinner thus giving lower indicated oil pressure. I was trying to find out what oli pressure is low enough to harm engine.

Thanks

Mike

[41ford1]

I see similar readings in my 59ab. I am going to check the releaf valve per what GM said in one of his posts. Could be the spring is relaxing as it warms up. I am running 20-50 oil and have a stock filter. I have checked the pressure with a mechanical gauge with both filter and no filter. Same readings both ways. The engine sounds good, runs good. As long as there is some pressure shown oil is being moved. I've run it this way for about 5 years. I have no idea how much longer it's been run this way.

[Old Henry]

Sponsored Links (Register now to hide all advertisements)

In my opinion, any oil pressure indicates that oil is flowing through the engine. I don't know about other flatheads but my 59A-B starts out 40-45# cold then when totally warmed up it runs at highway speeds at 20-30# but at low idle (600 rpm) drops to just a few lbs. like yours. It's a newly rebuilt engine with new 80# pump and 40 straight weight oil. Like I said, I figure if there's any pressure of any amount the oil is flowing through the engine and all is well.

[Old Henry]

According to George McNicholl, author of "How to Build Ford Flathead V-8 Horsepower", Ford designed the 46-48 flathead engine block oil-relief valve to open at 30 psi. Melling's 49-53 M-19 standard-volume oil pump pressure-relief valve is designed to open at 50 psi. Read more here: http://books.google.com/books?id=ItB...0valve&f=false

I've always thought 30 psi. was "normal" since it's in the middle of the gauge. The above seems to back that up.

P.S. What I don't get is why the relief valve opens at 30 psi for an 80# pump that was standard??? Maybe just to provide sufficient volume at low rpms?

[Mike in Louisiana]

Thank you for sharing what you have seen with your engines it helps alot.

This truck has come along ways with the help of everyone on the ford barn.

Thanks

Mike

[Bassman/NZ]

I've had flatheads in the past that showed almost no oil pressure at hot idle. I may be wrong but I think it's par for the course.

[Brendan]

my old motor had 20 lb on a cold start, and 7 lb when it was warm

[flatjack9]

If it runs good and doesn't make any odd noises, drive it. Put a piece of tape over the pressure gauge.

[Bassman/NZ]

Originally Posted by flatjack9

If it runs good and doesn't make any odd noises, drive it. Put a piece of tape over the pressure gauge.

hahahaha.... now we're talking!

[Old Henry]

Here's one more thought while you're sitting at the red light watching the oil pressure go to a few measly pounds. Just think about the fuel pump that takes no more than 3 1/2 pounds of pressure to provide all of the gas the engine needs at any speed. Remember, pressure does nothing for the engine. It's flow that is all it needs. Again, in my opinion, any pressure indicates flow which is all you really need. So, maybe that tape over the gauge isn't such a bad idea after all.

[Mart]

You could draw a needle on the tape pointing at 30 to make you feel better.

Mart.

[46ford]

Originally Posted by flatjack9

If it runs good and doesn't make any odd noises, drive it. Put a piece of tape over the pressure gauge.

My flight instructor used to do that when I got fixated on a gauge.

[Fibber Mcgee]

I've heard many times that with a flathead if you have any oil pressure your good,I hope thats true because thats what I'm counting on.

[Brendan]

i used to work in a Body shop, and they had 1964 Ford tow truck with a 292, when you would first start the truck it would have 50 lb, but when warmed up it would drop to 0 lb, it ran for years like that!

[G.M.]

40 lbs at speed and 15 idle is what ALL of these, engines will produce unless there is a problem. Worn pump, dirty screen, loose pick up tube leak behind the fly wheel which would run out the cotter pin hole. Realy loose bearings or cam bushings which I think would have to be pretty bad. All of the oil pressure problems I have found on normal running engines have been worn pomps, oil pick up and mainly the bypass valve up front or the bypass valve in the latter pumps. Everyone I found was an easy fix. 20/50 gets the best oil pressure and 15/40 looks almost the same. Light oil in an older engine usually produces lower oil pressure. G.M.

[Rocketsled]

Oil FLOW is what you need. Pressure is resistance to flow. Motor oil starts out as #20 and is souped up with all kinds of additives. When the additives are depleted the oil is still #20. The old timers around here used HD-20W year 'round and it works fine. Additives that improve cold flow and visocity and turn #20 into 10W-30 work fine. When you stretch the range to more than 3 grades the additive depletion rate can vary. Good base oil with fewer additives is preferable to a poor base oil loaded up with metallic junk.

[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