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Technical Somebody 'Splain Me Oil Pumps and Oil Pressure

Discussion in 'The Hokey Ass Message Board' started by Truck64, Oct 8, 2019.

  1. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Maybe 2nd only to "What Oil Should I Use?" is the subject of oil pressure, how much is "enough", how much is "too much", what is the proper oil pressure at idle, cruising, etc. I utilized the idiot light on the dash for my Y Block for a long time. I estimated that the oil flow to the rocker shafts and rockers was "OK"by eyeballing the flow at idle. Probably not too swift.

    After replacing the oil pump on GP it sure looks like the flow up top has improved a fair bit. When warmed up there is a nice "singing" machinery sounding noise, for lack of a better term. Did replace rocker shafts and rocker arms recently, so they don't have excessive clearances. I bought a mechanical gauge, it measures just under 60 pounds at cold idle on startup, and 35 pounds at hot idle, and about 60 pounds at 2000 RPM. The book says 35-55 hot at 2000. So maybe a bit high? 10w-40 NAPA house brand erl. Do I need to be concerned. I tested it after about a 10 mile highway run, good and warmed up, though not HOT like summertime temps.

    I don't have it plumbed into the cabin yet, one thing I'm wondering if numbers are otherwise good, is how this bypass or relief valve works out on the road. I get that it bypasses when the oil is cold and thick, or at high speed or wide open throttle.

    What about when just at cruise, say a steady 60 mph? Is it designed to throttle the pressure back to the predetermined spring opening point, whatever that may be, and maintain this?
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    it's a bypass valve...it works by pressurized oil pushing against the face of the valve, and has a spring that resists moving. As soon as the oil pushes with enough force on the end of the valve, to move it against the spring far enough to begin to open the valve, pressure will drop a little bit, and the valve will move "closed". so, it won't "throttle" the pressure until it reaches it's set pressure rating.

    Sounds like you are looking for things to worry about....

    If it's getting oil up there, then it probably has "good enough" condition cam bearings, and the passages are not plugged.

    An engine will run a very long time with surprisingly little oil pressure. Keep in mind that pressure is used to get oil to the bearings, and as long as there is oil at the bearings, oil can do it's lubricating job. Having more oil pressure showing on the gauge, does not improve lubrication. And using thinner oil may result in oil being able to get to the bearings more easily.

    It's a highly misunderstood subject.
     
  3. tubman
    Joined: May 16, 2007
    Posts: 6,913

    tubman
    ALLIANCE MEMBER

    Too much pressure can be a [problem. I have a 327 in my Corvette that I had a complete rebuild done on. The builder did me the "favor" of installing a hi-volume/hi-pressure pump, because it was about half the price of a regular pump. To make a long story short, I had to replace the pump and the valve guide seals to get an engine that didn't go through a quart of oil every two tanks of gas and peg the gauge, even at hot idle .

    Hi-Volume/hi-pressure pumps are for specially built racing engine specifically built with larger than normal bearing clearances. They have no place in a street engine.

    That being said, Jim is right in saying that you are worrying about a non-issue. Your pressure is a little high, but not excessively so. It's a good thing you are keeping an eye on it, given "Y"-blocks reputation for top-end lubrication problems.
     
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  4. Beanscoot
    Joined: May 14, 2008
    Posts: 3,053

    Beanscoot
    Member

    Cynical me thinks that "High-volume" oil pumps are also a crutch for auto machine shops that can't hold tolerances when regrinding cranks, to compensate for sloppy clearances.
     
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  5. onetrickpony
    Joined: Sep 21, 2010
    Posts: 753

    onetrickpony
    Member
    from Texas

    The old adage of 10 pounds per thousand RPM is what I grew up with. It never caused any excessive oil consumption on a fresh engine. I prefer a minimum of 20 pounds at idle, but that is just my own rule. I can't say that it actually helps anything.

    A pegged out gauge is usually caused by a stuck relief valve in the pump, not just because it is a hi-vol/hi-pressure pump. The relief valve sets the max pressure on the system. I have run many miles with a high volume pump on the street with no problems at all. No flooding valve seals, no pumping the pan dry, nothing. The only time I ever saw a problem was someone trying to band-aid an old dirty engine with low pressure by installing a high pressure pump. All the problems that they had were related to gunked up passages and lack of oil return volume to the pan.

    I do know that modern engines run with super thin oils and very low pressures that would probably scare the crap out of me if I saw it on a gauge.
     
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  6. 57JoeFoMoPar
    Joined: Sep 14, 2004
    Posts: 6,138

    57JoeFoMoPar
    Member

    It's interesting this topic should come up. I'm laying my ground work to yank the 394 out of my 61 Super 88 largely because of oil pressure issues.

    So I got this car, and while it was getting a little hot in traffic one day while still shaking it down, the oil pressure light started to flicker, then immediately go out as soon as I stepped on the gas to bring the rpms up a bit. I got home, put a mechanical gauge on it, which confirmed my fears. Mind you, the engine was running fine. No noises, knocks, taps, etc. 05E17D91-131B-44E2-8383-EAB5AC857334.JPG

    This was with 15/40 in the engine. I drained that oil out, and put in 3 quarts of Valvoline VR1 SAE 50 with 2 quarts of Lucas. That gave me a whopping 7-8 psi at warm idle, and 30-35 psi going down the road, which was the same as with the 15/40. Problem is now that the oil is basically the consistency of maple syrup, and on extended runs on the highway, the lifters will bleed down and tap, until I get off the highway, and get the rpms down for a while, and lifters pump back up again.

    The question I've always had is what is how much oil pressure is too little? What's too much?
     
  7. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    If the bearings get so little oil that there is metal to metal contact, with no oil film between them, then you've gotten to the "too low" point.

    Too high? That's harder to define.
     
  8. tubman
    Joined: May 16, 2007
    Posts: 6,913

    tubman
    ALLIANCE MEMBER

    Too high for me was a pegged 60 lb oil pressure gauge, even at hot idle.
     
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  9. 57JoeFoMoPar
    Joined: Sep 14, 2004
    Posts: 6,138

    57JoeFoMoPar
    Member

    My 383 Mopars have always run 75-80 psi going down the road, 40-45 lbs hot idle. I feel like it depends on the engine, each one is different.
     
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  10. J. A. Miller
    Joined: Dec 30, 2010
    Posts: 2,057

    J. A. Miller
    ALLIANCE MEMBER
    from Central NY

    I like the old "Rule of thumb" - 10psi for every 1000 rpm.
     
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  11. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
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    from Ioway

    Funny you should say that, No, that's kind of why I relied on the Idiot Light for so long - I figured if I didn't have an oil pressure gauge, it would be one less thing to worry about. But it's important enough to keep an eye on. The light just informs "your motor is now lunched" right?

    I paid a shop to rebuild an engine a long time ago and wasn't up to speed on what they should have done. A fresh oil pump falls in that category. I did notice some paint marker #s written on the first crank throw while replacing the timing set, so somebody at least installed new bearings, right? I didn't drop the pan to actually check clearances. I figured oil pressure would more or less tell the tale.

    What I should have done was measure twice and cut once, but I thought a new oil pump wouldn't hurt anything. Pump rod was chewed up a little, retaining clip installed on the wrong end, and some Gomer used liberal quantities of RTV to seal the oil pump to the block. I'm lucky a piece didn't break off and plug up in an oil gallery. I must have pulled the distributor a dozen times for curving and other purposes, though never pulled the pump rod thankfully.

    Both heads appear to get a good oil flow at rockers, and the overflow tubes have a steady stream. Book calls for 10w-30, it may be I'm overthinking and 10w-40 or 20w-50 Rotella is too stout?
     
  12. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Ok, though then the question is what actually causes that? A restriction somewhere as in a plugged up gallery, or a stuck relief valve? Or both?
     
  13. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,795

    jimmy six
    ALLIANCE MEMBER

    If you want high pressure on your gauge have the machinist keep your connecting rod side clearance to a minimum. I run .018" on my GMC's (that's .009" on a side) and .021" on our V8's which has 3 sides and want the flow and will sacrifice pressure for it.
    Ford Y-Blocks get a bad rap from using non detergent oil in the old days because they didn't have hydraulic lifters. My parents Fords were the same. That and in-town-stop-go never warmed up killed my moms. Today I use 10-30 in mine and it's never shown an oiling problem. I change at 2000 miles.
     
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  14. 10 psi/1000r is ok. In fact, oil pressure has nothing to do with lubrication. It is there to make sure adequate oil is available to the bearing and to flush out oil heated by the friction in the lube process. Any more pressure just uses power and wears out the pumping system. Street/strip engines do not need hi pressure or hi volume pumps. They do more harm than good.

    Engine bearings use hydrodynamic lubrication. The journal spinning in the bearing drags oil via friction into a small clearance between the two parts. The higher the load, the higher the pressure generated in this clearance. The pressure can reach several 1000psi and is always enough to suspend the journal above the bearing with properly designed oil. In a perfect world, there would never be metal to metal contact due to the high pressure oil film. In the real world, oil contamination, cold dry starts, etc. results in metal to metal wear. Engineers design oils that have adequate viscosity to maintain film strength and suspend the journal while having not so much viscosity that it has drag and over heats from friction.

    Hydrodynamic lubrication was actually discovered in the early days of railroading where a lot of mechanical engineering was discovered. They built the railcar trucks with axles and solid bushings, envisioning the axles running in animal fat lube and metal on metal on the bronze bushings. They drilled bung holes in the tops of the bushing bosses, poured in the grease and pounded in hole plugs. They kept finding the hole plugs blown out no matter how tightly they plugged them, and realized there was many times more pressure in the bearing clearance than car weight could account for.

    Making a short story long, most engines get by just fine with stock oil pumps which pump more oil than the engine ever needs and just vents the excess out the pressure relief valve.
     
  15. Diavolo
    Joined: Apr 1, 2009
    Posts: 824

    Diavolo
    Member

    10#/1000rpm. That's what bobistheoilguy says and I consider his knowledge and background to be extensive so that's what I'm going to go by.

    Unless your clearances are shot or have a broken pump shaft, your problem will never be too little lubrication. Too thick and you run into the problem of oil getting into all those tiny places it's supposed to go when it's cold.
     
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  16. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Don't doubt the 10#s per thousand but I couldn't find anything on oil pumps looking over the site itself. The forum section is OK but there are more than a few loons therein.
     
  17. Truck,
    Your oil and pump are fine,,,,60 pounds is great.
    The pressure relief is constantly being pushed back to limit pressure,,,that is what bleeds the pressure down.
    Sounds very good to me.

    Tommy
     
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  18. Boneyard51
    Joined: Dec 10, 2017
    Posts: 6,440

    Boneyard51
    Member

    Remember the pressure on the gauge shows you what is NOT going through your bearings/ engine! Think about it!






    Bones
     
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  19. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    Nice job willys36, this is correct. It's rare to see good info like this posted, I commend you.

    Let's go back to the question in the thread title. Pumps produce flow, not pressure. This is a basic of fluid dynamics and of hydraulic engineering. That's the first thing to get in your mind, the pump is merely moving fluid from the inlet to the outlet. Pressure builds as a result of resistance to that flow. The resistance can vary due to internal clearances in the engine, and it will vary with viscosity of the oil. In fact, technical definition of viscosity is "resistance to flow"; a fluid with low viscosity will flow easily, and fluid with high viscosity will resist flowing. So a pump will move x gallons of fluid per minute at a fixed rpm, and the resulting pressure in the system will be higher with a higher viscosity oil than it will be with a lower viscosity oil. So these are the basics.

    So then you asked this: "
    Well, go back to the basics, it a restriction to flow that causes pressure. There really was no information in the post that describes the condition, so all you can do is make a WAG. It could've been from a plugged oil gallery, but that's pretty rare, isnt it? Relief valves don't cause the pressure to go up, they relieve it when it get's too high. IMO there's too little information provided to determine the cause, but pressure is ALWAYS a result of restriction to flow, so that is the basic answer. What was the cause of the restriction in that case? Don't know.

    How much pressure is needed? Well, as @willys36 posted above, ANY pressure at all indicates there is sufficient oil in the galley to ensure enough oil to properly lubricate the bearings, because it is by hydrodynamic action that the bearings are lubricated, not pressure from the pump. The pressure in the pump does not lift the crank and keep the journal separated from the bearings, hydrodynamic lubrication does that. That's the next thing to get right, pressure in the system is merely an indication of sufficient supply. With that said, automotive engineers like to see a minimum pressure of about 10 psi, because if it drops below that, it indicates that the flow of oil is less than normal, and the pressure could drop to zero real damn quick. So idiot lights are usually set around 10 psi. And you should see higher pressure than that at elevated RPM's, because the faster the pump works, the more oil it pumps, and subsequently the higher the pressure you should see. If you only see 10 psi at say 3500 rpm, when the rpms drop to idle speed the amount of oil flow will probably be insufficient to maintain adequate supply to the galleys.

    That's a long row to how to get to the answer, there are no fast and hard numbers, there re general answers, unless you are talking about specific engines, than we can refer to the manuals for that specific engine. But in general, you should see at least 8 - 10 psi at idle, and at higher rpm's the pressure should increase. How much depends on the individual engine and the oil used. The 10#'s per 1000 rpms is a general statement; it's not bad, but it's not carved in stone either.
     
  20. The type and viscosity of the oil you use, is a matter of what climate you are living in and the condition of the engine. When the engine is finished the break in cycle, I prefer to use synthetic oil and the best quality filters. The mileage In my daily drivers over the years, normally improved 5% or more, when the engine, transmission, transfer case, and differentials were changed to synthetic.
    Even with synthetic oils, they are not all the same. The North American standards are not as strict as the European standards, but a little research will produce results. I use Amsoil, and there are oils to meet all automotive needs, as well as an extended change interval that makes the cost about even without even considering the mileage improvement.
    I have a lot of experience using synthetic oils, I have been using them for every type of automotive use, 2 cycle engines, and aircraft.
    Warning, you can't use a good oil in junk and expect that it will improve the performance of a sick engine.
    As for oil pressure, using a high volume pump for high rpm use, can cause more problems that it will cure. The rule that I learned was, 10 psi for every thousand rpm.
    Bob
     
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  21. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Debris in the crankcase picked up by the pump can cause problems. Bits of wire, or RTV, etc., if the relief valve happens to stick open and doesn't close the pressure will be low, but if the relief valve is stuck closed it would have excessive pressure because there's no bypass, wouldn't it? At least that is my understanding from reading Melling docs. The valve can also stick partially open/closed, too. Really interesting subject, thanks for your participation, and everybody else too who responded. Thanks a lot.

    I'm told oil in a Y-block should have at least a 40 somewhere in the classification. The operator's manual says 10w-30 in "practically all cases" is suitable for most weather conditions, it recommends 5w-20 for sustained operation in temps below -10° F. Seems to me 10w-30 would flow a little better maybe than 10w-40. I believe the recommendations for a 40wt or better today are because of the lower zinc and phosphorous levels in the motor oils today and concern about flat tappets and cam lobes etc.
     
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  22. GTS225
    Joined: Jul 2, 2006
    Posts: 1,244

    GTS225
    Member

    Everybody go back and re-read Blues4U's response. He's right in his rudimentary explanation. (I say rudimentary because there's more detail than we can present here. Fluid dynamics can easily be a seperate class at an advanced tech school.)
    He may not have carried his explanation of the relief valve far enough, but that could be construed as small details.
    As he said, the relief valve is spring loaded, and is typically not adjustable to the layman. A relief valve could get stuck in the closed position, causing an over, or high pressure condition. It could get stuck in the open position, causing low pressure, or worse, no pressure. This may be caused by debris caught between the relief valves seat(s), perhaps scoring and binding, or worse, a broken spring.
    Low pressure in a high-mileage, internal combustion engine, will most likely be caused by excessive bearing clearances. This can be mains, rods, or cam bearings, but bear in mind that oil also gets pushed to the top end for valve train lube, too.

    Just some food for thought.....Roger
     
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  23. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,213

    sunbeam
    Member

    High Oil pressure is required for high RPM in engines that have large mains. The oil has to over come the centrifugal force to push the oil to center of the main so that it can go on it's way to the rod bearing. A 3"main at 7000 rpm requires quite a bit of pressure. Pressure only delivers the oil you only need enough to get it there.
     
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  24. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    It sounds like installing 20w-50 isn't maybe the best idea in a motor with excessive bearing clearances? The gauge will display more pressure, but that doesn't necessarily translate to more flow?

    Shimming up the relief valve spring generally doesn't sound like a good plan either.
     
  25. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,213

    sunbeam
    Member

    There are many bearings in the motor all fed from the same pump one bearing using more oil will effect the other bearings. So if you slow down the loss at that bearing with heaver oil the rest will be better off. it's all about keeping an oil film on all the bearings
     
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  26. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Well OK, that makes sense too.
     
  27. Something will break. These are positive displacement pumps. That means if it makes a revolution, it transfers X volume of oil, whether the downstream passage is open or not. Close the passage and something has to break if there is no relief valve. I try to avoid pumping bits of wire!!!!!!!!
     
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  28. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    You know the old saying ... "if ignorance is bliss, tis folly to be wise". I tried not to worry about it. Drove all over the country several times with only the dummy light. Never seen it even glow dimly, ever. When removing the old pump the gasket had been coated with RTV, all it would have taken was a goober to break free and plug up an oil gallery. Or the relief valve. Bad Things happen with excessive pressure, blowing off oil filters or core plugs in the heads if it's real high.
     
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  29. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    Interesting question. So the relief valve only comes into play when the pressure exceeds the point where the spring holds the valve closed, and that should only be temporary, not constant. When the relief valve is opened due to pressure and the oil escapes past the valve and returned the the sump, there is a lot of shearing of the oil that occurs, which causes heating of the oil. If the valve remained opened all the time, limiting the pressure constantly at the opening pressure of the valve, the oil would runs excessively hot, leading to issues with oxidation and sludge and varnish deposits. Plus, if the oil in use is a multi-viscosity oil, like 10W-30 or 20W-50, the polymers that provide that mutli-viscosity performance will shear resulting in a permanent viscosity loss. Relief valves are not designed or intended to be operated in the open position constantly, or working at that point,opening and closing constantly. If this is the case then something else is going on, i.e. too high viscosity of oil. I'm not sure what the Melling doc's you mentioned said, but I don't think they intended to imply that the relief valve is constantly in operation, it is there for momentary relief of high pressure conditions only.
     
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  30. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    I've seen this in high pressure hydraulic systems that operate at >6000 psi, but never in an engine. But yes, the oil has to go somewhere, if there is a blockage in the system and the pressure relief valve is stuck closed something has to give.
     
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