What's up with my oil pressure?

[Talkwrench]

As far as I know my motor is in great condition. I was told it has only done a few thousand miles when I bought it. Goes really well, very responsive and has no probs doing 60 climbs higher if I'm not watching it, easy.. And it's pick up. I do have a problem with oil pressure. Starting is fine I've seen it go as high as 65 but as soon as the motor gets up to temp 180 and over the oil pressure drops off, it worries me on the freeway at the speeds I do the pressure is falling away as normal cruise say 45 when hot it's only got about 25 psi. And when you pull up at the lights it's virtually nothing. I'm using Penrite HPR 30 which is a good quality oil 20-50 in fact it's a 20-60 and has plenty of zinc. I'm starting to question if its the oil as my Y block does the same? What sort of oil pressure should I expect?

[31chevy]

I think you are ok, my 34 with a 37 block has almost the same readings as you describe & has about 1200 miles on it since complete overhaul. There are other Barners who can give you more & better info than I can. As I understand it oil flow is more important than oil pressure in these flatheads same goes for VW's.
Gary.

[G.M.]

How much over 180 does your engine temperature get?? Do a dipstick drip test. Pull the dipstick before starting when the engine is cold. Watch how drops of oil drip off the stick watching the consistency. After the engine gets to 180 do the same test. I would bet the oil gets very thin. Also the bypass valve in the oil pump or in front of the intake valley could have a week spring. G.M.

[Mike51Merc]

Sounds normal to me.

[joe 1950]

are you reading off the dash gauge, if so you need to put a master oil gauge in place of it just to make sure of the readings, i use a #40 oil with a lucas oil supplement ,on a 90- degree day i still have 30lbs at idle

[Fe26]

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I agree with Joe, check the pressure with a Master Gauge. BTW these flatties will run with under ten Llbs of pressure.

[RMR&C]

Originally Posted by joe 1950

are you reading off the dash gauge, if so you need to put a master oil gauge in place of it just to make sure of the readings, i use a #40 oil with a lucas oil supplement ,on a 90- degree day i still have 30lbs at idle

Yep, my dash gauge read 30 psi at cruise and almost 0 at hot idle. I installed a SW mechanical oil gauge and wow! 50 psi at cruise and 10-15 at hot idle. This on a well used 8ba....

[Bill OH]

Try a different oil pressure sender - I have had them go bad. Also, make sure the connections on the oil pressure guage are clean and tight.

[ford3]

the trouble with the flathead is that ford never gave an oil pressure reading at idle, all that is given is #30 at 30 miles an hour, and as 31chevy posted, oil flow is the important thing

[G.M.]

How do you have oil flow without pressure?? If the oil is flowing that freely through the bearings the bearings are warn out. I built a tester to test the oil pumps. From what I have seen in testing dozens I wouldn't put an oil pump on without first testing it new or used. When Skip rebuilt his 37 engine he put the pump in a pan of oil and turned it by hand, after 2 turns of the drive gear by hand it pumped a good strong looking stream of oil and said that looks like a good one. I said we better test it anyway. We removed the drive gear and attached a 1/2" drill and it pumped out a good stream but as soon as we restricted it the pressure gauge dropped to zero. Found another pump and it put out 90 LBs when restricted. The output pressure is then adjusted on the pressure valve in the front of the engine. I found most springs are weak and require a piece of 1/8" brass pipe about 3/16' long on top of the spring to get about 55 LBs of pressure at highway speeds. Even with the engine sitting on the floor I remove the plugs and lub the cylinders with the intake manifold off and mechanical gauge screwed into where the sender go's spin the engine with 12 volts. The pressure you see will be the pressure you get driving at 50 MPH. You can adjust the shim to get the pressure you want. Later pumps also have a bypass valve on the pump and need to be adjusted with the test unit before installing. I have seen later pumps in the car lose pressure after the engine runs a while. Pulled the pump and found it losing pressure after a few minutes on the tester. Adjusted the pump valve and problem solved. G.M.

[Old Henry]

Your readings are the same as mine on my 59A-B in my '47.

If you want to hook up a mechanical gauge just to check here's how: https://www.fordbarn.com/forum/showthread.php?t=68156

As others have said, flow is more important than pressure and any pressure indicates the oil is flowing to where it needs to be.

Many have suggested that, if the reading on the oil pressure gauge is really bugging you, put some tape over it. That's how critical oil pressure is.

That being said, I run S.A.E. 40 in my engine in the summer (over 60° F) just so's I can see a little more pressure on the gauge. It adds 5-10 lbs.

[bugsiegel]

I had a similar issue. Rebuilt engine on a sitting a long time truck. Oil pressure was fine for the fist two weeks and then starting reading low. After a little panic, added a second gauge and the new gauge was reading much higher. Changed the sender unit for the factory gauge and then they both read normal. Took the aftermarket gauge out now.
Off my memory, my engine builder said this engine only needs 8 # of pressure per 1000 rpm.

[Old Henry]

BALANCE BETWEEN FLOW AND PRESSURE
Since none of the wear surfaces on a stock flathead engine require pressure to protect them flow is all that is needed - just some oil there to lubricate the two rubbing surfaces. Of course, without any pressure there would be no flow so some presssure is necessary. However, there is an extreme the other direction. If pressure is what you think is most important and what you want to see most of all such can be created by restricting flow. Think about it. Ultimately, the most pressure you could see on your gauge is with all flow restricted to zero and the bypass valve on the oil pump eliminated. Who knows how much pressure you'd then see on the gauge. I'm thinking beyond its limits to measure. Would that be the best condition for the engine? Obviously not.

Ford designed the oil pump, oil passages, and bypass valve on the oil pump to limit the oil pressure to about 30 p.s.i. which is what most gauges show when the engine is first started and the oil is cold and thick. When the oil heats up it thins out and the pressure reduces but the flow increases. Think about it. Thinner oil, that shows lower pressure, is going to go where it needs to go better than thicker oil that shows higher pressure. There is, of course, no need for more than the 30 lbs. pressure Ford designed the systems for.

P.S. Regarding modifying the oil pressure bypass valve to increase pressure as has been suggested; it is important to understand that such valve is only a safety feature. It is only to limit the maximum pressure in the lubrication system under high engine RPM's. Like the thermostat that limits the bottom temperature an engine can run at but not the maximum, the blow by valve does nothing to increase oil pressure when such is less than will open that valve. Since the valve doesn't open until the pressure is above 30 p.s.i. it is totally closed at any pressure lower than that. It can't get any more closed than totally closed and has no way to increase pressures below its "blow by" pressure. Why would anyone want to modify the safety valve so that it will not open at the safe pressure of 30 p.s.i. that it was designed to do ??? Doesn't make sense does it.

If one really wants to see an increase in the lower pressures, below that which opens the safety blow by valve on the oil pump, modifying the safety valve will do nothing. The only way to increase the pressure below that limit is to restrict the flow by closing off some oil passages.* Why would anyone want to do that??? Or, you can run thicker oil (like I do). Those are the only two ways. Nothing more.

*Note: To get the flow of oil to go through the engine more and the oil filter less it is important that the fitting on the oil filter where the oil enters it has the restriction in it. Without such, too much oil will go through the filter, too little through the engine, and the pressure will, indeed, show lower.

[G.M.]

Low oil pressure is not normal I don't care how many people say it is. Low oil pressure indicates something is not right. I have never had low oil pressure that I couldn't fix. Low oil not caused by worn parts can be fixed. Over a long period of time low oil pressure has to cause more wear on parts. G.M.

[Old Henry]

Originally Posted by G.M.

. . . I don't care how many people say it . . .

That pretty much goes without saying.

[donald1950]

GMs concept on his "oil drip test" is utterly worthless.
how fast hot oil drips off a dip stick has nothing to do with viscosity and oil flow under different tempatures.
here is an article on oil viscosity and how mulit weight oils function. it is real world from AmsOil of how oil works, how mulit grade oils operats, what makes them mulit weight oils, not of how oil drips in GM fantisy land of Florida and Penna.

http://www.upmpg.com/tech_articles/motoroil_viscosity/

i have posted this article several times before about his "drip concept" but i doubt he has read it since he still encourges the "drip method" and he is the "expert"

don

[46deluxe]

Most guys use the HPR50 here in Aus , give it a try .

[4t8v8]

Same as RMR&C. Those original sending units and gauges weren't very accurate. After 2 orig. ending units and 2 different gauges I still get 0# at idle and 25-30# at 50mph. On my SW gauge 10-15# at idle, 55# at 50mph.

[ford3]

G M is very passionate about this, but ford didnt sem to worried about the low oil pressure at idle, if he was he would have given a pressure reading at idle instead of at speed, as for me i would rather have 5 gallons a minute flowing past my bearings at low pressure than one pint at 60 or 70# a minute

[David J]

Not exactly on subject but I would think I was in heaven if I ever had a STOCK 33-34 with 10#'s of oil pressure at idle hot . I don't care what weight you use these early STOCK motors don't carry good oil pressure at idle hot .