Technical Oil Flow or Oil Pressure

Antique engines didn't even have a water pump, or a radiator, the water moved through the engine by convection. And some did have a crude radiator, nothing enclosed, just an open grate that the water ran over and collected in a pan until it was sucked back into the engine (by convection). You couldn't get a much slower rate of cycling. I wonder why they don't use that anymore?

 

If Cummins tried it but discontinued its use,,,,you can bet there was a problem with it .
Flow is very important,,,,especially for a coolant system .

This tread is about oil pressure,,,,,,and of course,,,oil flow .
Some of the older systems didn’t need a ton of pressure .

Some engines relied entirely on splash,,,,,and they worked fine for what they were .
Low compression,,,,,low rpm,,,, splash will lubricate it fine .
Then the performance and rpm gets raised with compression and more load ,,,,,then lifters gall,,,,bearings burn,,,,,rockers and pushrods gall .

I believe in pressure,,,,at least in any application I am associated with .
Even the Motors manuals calls out factory oil pressure readings .
Now the engine can probably get by with less,,,,,but,, how much less is in the eye of the beholder .

Tommy

 

Ebbspeed said:

I said:
Take a spare crossflow radiator and lean it against a wall. Put a hose on what would be the inlet tube from the engine and tilt the hose upward. Now pour water into the hose and see if it doesn't come out the discharge tube on the other side of the radiator. It had to flow thru the crossflow tubes to get there and there is no pump involved.
The water pump moves the coolant to the radiator and keeps the header tank supplied. If the water had a pressure head, as soon as you removed the radiator cap on any engine, the pump would immediately push water out of the cap opening.

Don't know why you try to twist things I say into things I didn't say, or why you can't have a discussion without all the personal drama.

My response above suggested a simple way to use an unmounted spare radiator to find out if water will flow thru a crossflow radiator without being assisted by a pump. There will be no pressure involved other than the weight of the water itself . I guarantee you water will flow thru a crossflow radiator with gravity doing the work.

When you move to the scenario where the radiator is mounted in a car and you just started the engine, you can remove the radiator cap and no water will escape and burn you.

When the engine has warmed sufficiently to operating temp or above, removing the cap will reveal pressure. The point here is that the pressure created by being pumped to the radiator is not the same as the pressure created by expansion due to being heated. Two different kinds of pressure. If at that point you shut the engine off (stopping the water pump ), the pressure in the system will still exist even though the pump has stopped. Again, system pressure is there because of heat, not because of the pump.

 

I apologize for the drama. You seem to come up with a lot of things that make me shake my head. Look, this thread is about oil flow & pressure. I'm not clear on how it got on to coolant flow, but maybe it would be best to let it go and let this thread get back to oil.

 

Yes, and my apologies for contributing to the thread drift. We often seem to be on the opposite side of issues but I assure you I try to be honest about what I'm saying. You are correct that I cannot provide proof that water flows thru a radiator in a car by gravity. Closest I could get was a quote that said "the pump returns the water to the top of the radiator". The things that cause me to think its gravity also make me realize that there are times when I think the pump provides assistance too. The key to me is the operation of the thermostat. It controls how much flow takes place. When it is partially open it limits the flow back to the radiator and would seem to make it hard to have much if any pressure at the top of the radiator. Open it all the way and have the engine at higher (2500 rpm) going down the road and I can see that enough flow could happen that it could have sufficient resistance by the radiator tubes that the pump works to push the water thru. Thats just how I think it happens.........and I have been wrong before. So, no hard feelings on this end and lets get back to the ops original question about "pressure vs flow"

 

I have participated in this thread and had a hand in it’s drift, sorry about that. But I have alway respected Bluse4U and ekimmeirbo! Both are learned men, in my opinion. But noboby agrees all the time.
But on the car radiator, the flow is a result of differences of pressure. The car water pump is a centrifugal pump . These pumps have to have pressure at the intake to operate.
If you put a gauge right at the intake of the pump and one at the discharge of the pump, you would see a difference in pressure even though you have 5 to 17 psi on the whole system.
That’s how you get flow in a car’s cooling system.






Bones

 

The purpose of lubricants is to form a low-friction layer between moving parts, remove contaminants, and remove heat.

That latter two suggest that you if you have a high oil pressure but little flow, the oil will not be doing its job (i.e. it's more like grease than oil). So I'd be in the "flow" camp.

 

I agree with most of your post, with the exception of “ oil can flow with no pressure “ . Oil or anything else needs a force to move. To get oil to flow, something HAS to push it, that something is pressure. It may be very small pressure, but it’s there.
I know this is just a technically , but you can have pressure with no flow, but to have flow, there has to be “some” pressure or force to move the oil.








Bones

 

I personally found the Melling videos posted to be very helpful in illustrating the issues.

That being said, after watching the Melling videos, it raised some questions for me. In an instance where an engine has low oil pressure due to wear and therefore larger bearing clearances, ultimately the loss of oil pressure is because the pump's constant rate of flow is inadequate to maintain the prior, pre-worn level of pressure. So, provided there is adequate supply of oil in the pan, is the answer to use a high volume pump, rather than a high pressure pump, because an increase in the rate of flow would help restore factory levels of pressure? Or did I totally butcher that up? Good topic.

 

You got it right.


Also one thing that I think hasn’t been mentioned, or I missed it, is an oil pump increases volume with speed. That is the faster it turns the more it pumps.
Also the faster the engine turns, the more oil it needs or uses.

The good thing about most engines and oil pumps is that the GPM of the oil pump increases at a faster rate than the engine’s need for oil. That is why the oil pressure increases with the rpm. ( most of the time) .

A high pressure oil pump will give more oil to the engine at high speed that a stock pump will due to more pressure pushing , or trying to push, the oil through the bearings. A high volume standard pressure pump will give more oil to the engine at low speeds, but the same amount of oil as a standard pump at high speeds. A high volume, high pressure pump will give more oil at all speeds.
But the question is “ what do you need?”.
That’s a whole new debate!


Edit: there are some variables involved here that I didn’t mention, just to keep it simple.







Bones

 

Way back when (early 60s) Dad and I did a lot of Y block Ford work. We had a parts source that would deliver a vatted and bored block, along with new pistons, rings, bearings and an oil pump kit. Of course picked up our old block as exchange. we did the rest. The oil pump 'kit' was interesting as we had the option of standard or high volume. Both had new rotor and internal lobed drive gear. The high volume included a thicker set and a machined spacer to put between the body and cover. Worked well, and helped with the Y block rocker arm oiling. More volume seemed to help the longevity. Special case there.

 

Worked, which is important. Today the cam bearing is grooved or the block is grooved At the same cam bearing for the extra flow of oil to the rockers.

 

I once owned a fully worn out 57 Pontiac. The old 347 leaked about everywhere it could. I didn't need an oil pressure gauge even tho 57 Pontiacs all came with a full set of gauges. I knew the pressure was going down when the hydraulic lifters began clacking..
My present hot rod has a 57 Pontiac engine and I set it up a tad loose...almost .003 on the mains. After putting guts from a melling high pressure in the stock pump [a new one] with 15W40 it idles at about 15psi and even hot it'll go to 60 psi at about 4000 rpm. I never worry about low pressure at idle.

 

Chryslers 3.6L V6 has a variable displacement oil pump but it only runs in two modes, low and high. The pressure that is developed varies based on load and RPM mostly though some other factors are used including temperature. The pump is driven off the end of the crankshaft unlike older designs that are driven off the cam at 1/2 crankshaft speed. An old style gear pump would not be able to turn 6000 rpm for long periods of time without bad things happening so this is a vane style pump. On most Chrysler vehicles with this V6 (almost all since 2012) you can bring the oil pressure up on the instrument cluster, at 1500 rpm cruise I normally see 35-40psi, wide open throttle 5000 rpm I have seen 120 psi. This engine uses 5W-20 oil.

 

Its funny how things work.......or at least how we define them. If you look at the scientific definition of "work", it requires movement in order to constitute "work".
For work, in the scientific sense, to be done, a force must be exerted and there must be displacement in the direction of the force. If you pick up a weight, you performed work. If you continue to hold that weight above your head for ten minutes after you lifted it there, scientifically you are doing no work. Now most of us would disagree with someone saying we are no longer performing work when we are holding a transmission in place while someone installs the mounting bolts.
In a similar scenario, to create pressure you must have resistance to the flow. If a fluid flows thru an orifice, the resistance of the orifice provides a means to create pressure.....especially if the oil is forced thru the orifice by some artificial mechanical device like an "oil pump". In actuality, when oil simply flows thru a hole or a tube/hose of its own volition (gravity), it is technically producing pressure because any time there is flow.........there is resistance. We tend to discount this resistance in an automotive oiling system and only consider the resistance of specific orifices in the engine as being responsible for providing resistance/pressure.
Now the amount of pressure provided by several quarts oil flowing through a hole at the bottom of a bucket is certainly minimal, but the weight of fluid can be very great in some instances (think oil refinery tank) and that same hole could provide significant pressure and volume. Going back to my original scenario about work, its often that the definition we use doesn't really define the whole circumstance, but as long as everyone understands that its just for simplification of explanation.......it "works".

 

I reckon that in most applications, the reason oil flow is monitored via oil pressure is that it is simpler and less expensive than installing apparatus that would monitor actual oil flow.

 

I would have to say that a person holding up a weight, transmission, or any object is actually doing work by that definition. It's not likely that anyone could hold any object absolutely still, they would be exerting force with their muscles to counteract the force of gravity, there would continually be a slight (not so slight with the transmission) amount of movement, and they would constantly be making minute (or not so minute) adjustments to keep the object in relatively the same spot.

 

Yes you could say that and be correct, but the idea was to use a simple example that most car builders could identify with. Sometimes the transmission will wiggle slightly other times it seats well and you just have to exert enough force to keep it in place. I used to lay under the car and get the transmission on my chest and knees and put in place when I had few tools. I guarantee it wiggled like you mentioned. Now I have a lift and a trans jack.........

 

I can't speak for the rest of the world but in small block Chevy world (and I will admit to having probably read this from something Smokey Yunick wrote) you need ten pounds (10 lbs) PSI (per square inch) of pressure per one thousand revolutions per minute 1,000 RPM. I'll do the math for you. If you rev it to seven grand (7,000 RPM) you would need 70 PSI. And, yes, high volume as well as high pressure oil pumps are available from various manufacturers. I prefer Melling pumps myself, even though this is not a paid endorsement, or a free one. Other opinions may differ. {Oh yeah. I forgot to add that Smokey also is supposed to have said, " An engine doesn't know what name is written on it. So the formula I gave you might also be applicable to other brands and variations.}

 

Get rid of the guage and put in a light. Because the guage is freaking you guys out! LOL.

 

But then the light comes on and you know you're REALLY screwed