Oil system myths

[gregcon]

I didn't read this whole thread but:

1) I believe the lobe style oil pump we use in in fact a PD style pump. It sure isn't centrifugal.

2) I'm not sure if we're arguing terminology or actual effect but I do believe a HV pump can create problems with a system that was already marginal when it used a normal pump is used. Part of that reason might be that pretty much every HV pump is also HP - high pressure. Without parsing all the details....if you have a stronger pump a-suckin' your oil, and the oil can't return fast enough, you can suck all the oil there is to suck.

A stock system, let's say, returns oil just slightly faster than it can suck it....so the pickup stays covered and happy.

Change to a more-sucky pump, and more oil is being sucked but nothing has been done to the system to improve the return. The pickup gets uncovered.

So while Tim Melling might be correct that an engine's tolerances determine how much oil you can 'use', that's at a given pressure. But raise the pressure? That equals more oil flow.

I could also believe that an engine's oil use is at times determined not by the tolerances, but by the oil pump/pickup itself. A stock pump might well run out of capacity at times...the engine would allow more oil to flow if the pump were to push it. But, the pump doesn't have the lobe capacity to fully satisfy the engine's ability, so you get less flow. Change to a HV pump and all of sudden the bearings are flowing more and the weak player becomes the sump capacity.

A big Achilles heel of the oil systems we use, for the most part, is the gravity return. Trying to route all that oil, too past a spinning crankshaft doesn't help matters.

 

[TT5.9mag]

Well, that is the thing, it's an opinion.
I have seen a propeller in water cavitate, and it sure looked like air to me.

It is air. And your opinion is still wrong.

Talk to a submariner.....Cavitation of the prop underwater is like telling the world your here in a permanent hide and seek environment. its the boiling of water at the tip of the props due to the negative pressure they create, lower boiling point at lower pressures. Not sure what the vacuum pressure of an oil pump is so its probably not an issue with an oil pump but the blanket term you need air to cavitate is not correct.

This right here.

 

[Phreakish]

I didn't read this whole thread but:

1) I believe the lobe style oil pump we use in in fact a PD style pump. It sure isn't centrifugal.

2) I'm not sure if we're arguing terminology or actual effect but I do believe a HV pump can create problems with a system that was already marginal when it used a normal pump is used. Part of that reason might be that pretty much every HV pump is also HP - high pressure. Without parsing all the details....if you have a stronger pump a-suckin' your oil, and the oil can't return fast enough, you can suck all the oil there is to suck.

A stock system, let's say, returns oil just slightly faster than it can suck it....so the pickup stays covered and happy.

Change to a more-sucky pump, and more oil is being sucked but nothing has been done to the system to improve the return. The pickup gets uncovered.

So while Tim Melling might be correct that an engine's tolerances determine how much oil you can 'use', that's at a given pressure. But raise the pressure? That equals more oil flow.

I could also believe that an engine's oil use is at times determined not by the tolerances, but by the oil pump/pickup itself. A stock pump might well run out of capacity at times...the engine would allow more oil to flow if the pump were to push it. But, the pump doesn't have the lobe capacity to fully satisfy the engine's ability, so you get less flow. Change to a HV pump and all of sudden the bearings are flowing more and the weak player becomes the sump capacity.

A big Achilles heel of the oil systems we use, for the most part, is the gravity return. Trying to route all that oil, too past a spinning crankshaft doesn't help matters.

The pressure relief valve sets the max operating pressure. A hv pump on am engine that can't consume hv volume will just spew more from the relief and right back into the pan. The risk isn't uncovering the pickup, but I think instead aerating the oil to the point of potential pressure loss when pumped.

 

[TT5.9mag]

I’ve never experienced sucking a pan dry before, or trapping enough oil up top to run the pump dry, but I know the Oldsmobile 455 guys have blown up lots and lots of engines claiming that reason. Ive built one olds 455 in my life for a jet boat and the first modification I did was add external oil drains to the valve covers because Mondello told me to.

 

[gregcon]

The pressure relief valve does set the pressure - but only against a 'dead head' presented by the rest of the engine. In other words, the pump will stop making pressure at 70PSI only after it sees a 71 PSI burden ahead of it. And in creating that 71PSI burden, more oil must flow as a result.

I agree aeration might well be another factor...that's why I said I didn't want to parse all the details, only the end result which is a loss of pressure due to no oil to suck. However it happens, I think it happens. Not in all engines, but some.

 

[oldkimmer]

I have never had a hv pump suck the pan dry. Kim

 

[SGBARRACUDA]

The pressure relief valve does set the pressure - but only against a 'dead head' presented by the rest of the engine. In other words, the pump will stop making pressure at 70PSI only after it sees a 71 PSI burden ahead of it. And in creating that 71PSI burden, more oil must flow as a result.

I agree aeration might well be another factor...that's why I said I didn't want to parse all the details, only the end result which is a loss of pressure due to no oil to suck. However it happens, I think it happens. Not in all engines, but some.

You keep mentioning "oil Sucking" how is that accomplished. So if I understand you right it is because the oil pump is submerged in oil is how your saying the oil oil is available at the inlet of the pump. Am I understanding you right?

 

[RustyRatRod]

The correct name for they type oil pumps Mopar engines use....at least the older ones I believe is called a gerotor pump.

 

[gregcon]

yes, but gerotor falls within a larger class of pumps which I believe are PDs.

 

[RustyRatRod]

yes, but gerotor falls within a larger class of pumps which I believe are PDs.

Yeah well, to channel Bones McCoy, "Dammit Greg, I'm a shade tree mechanic, not an engineer". lol

 

[yellow rose]

I didn't read this whole thread but:

1) I believe the lobe style oil pump we use in in fact a PD style pump. It sure isn't centrifugal.

2) I'm not sure if we're arguing terminology or actual effect but I do believe a HV pump can create problems with a system that was already marginal when it used a normal pump is used. Part of that reason might be that pretty much every HV pump is also HP - high pressure. Without parsing all the details....if you have a stronger pump a-suckin' your oil, and the oil can't return fast enough, you can suck all the oil there is to suck.

A stock system, let's say, returns oil just slightly faster than it can suck it....so the pickup stays covered and happy.

Change to a more-sucky pump, and more oil is being sucked but nothing has been done to the system to improve the return. The pickup gets uncovered.

So while Tim Melling might be correct that an engine's tolerances determine how much oil you can 'use', that's at a given pressure. But raise the pressure? That equals more oil flow.

I could also believe that an engine's oil use is at times determined not by the tolerances, but by the oil pump/pickup itself. A stock pump might well run out of capacity at times...the engine would allow more oil to flow if the pump were to push it. But, the pump doesn't have the lobe capacity to fully satisfy the engine's ability, so you get less flow. Change to a HV pump and all of sudden the bearings are flowing more and the weak player becomes the sump capacity.

A big Achilles heel of the oil systems we use, for the most part, is the gravity return. Trying to route all that oil, too past a spinning crankshaft doesn't help matters.

It wasn’t Tim Melling (don’t even know if there is. Tim Melling...I just don’t know) it is Tim Foster and he says what I already know.

An oil pump can not suck a pan dry unless the total leaks in the system are greater than the supply in the sump.

You can bolt on a pump with 100% more volume and the oil flow through the engine is the same. You may get more oil to the system sooner, and the system pressure my be higher (depends on the relief valve spring rate, although you can override the valve and spring) but you will not force more oil through the system. Oil will not compress.

 

[gregcon]

I wasn't actually ...positive....so I looked it up on Wikipedia:

A gerotor is a positive displacement pump. The name gerotor is derived from "generated rotor". A gerotor unit consists of an inner and outer rotor. The inner rotor has n teeth, while the outer rotor has n+1 teeth; with n defined as a natural number greater than or equal to 2. The axis of the inner rotor is offset from the axis of the outer rotor and both rotors rotate on their respective axes. The geometry of the two rotors partitions the volume between them into n different dynamically-changing volumes. During the assembly's rotation cycle, each of these volumes changes continuously, so any given volume first increases, and then decreases. An increase creates a vacuum. This vacuum creates suction, and hence, this part of the cycle is where the inlet is located. As a volume decreases compression occurs. During this compression period, fluids can be pumped, or, if they are gaseous fluids, compressed.

 

[gregcon]

But when you put more pressure into a system of leaks, there will be more leakage. Nothing needs to be compressed, as long as there are leaks for the oil to flow through.

If you are able to suck 1GPM, and force 1GPM through those leakage paths, your consumption is 1GPM.

But if you can only return .95GPM, you will eventually run out of oil.

 

[RustyRatRod]

I wasn't actually ...positive....so I looked it up on Wikipedia:

A gerotor is a positive displacement pump. The name gerotor is derived from "generated rotor". A gerotor unit consists of an inner and outer rotor. The inner rotor has n teeth, while the outer rotor has n+1 teeth; with n defined as a natural number greater than or equal to 2. The axis of the inner rotor is offset from the axis of the outer rotor and both rotors rotate on their respective axes. The geometry of the two rotors partitions the volume between them into n different dynamically-changing volumes. During the assembly's rotation cycle, each of these volumes changes continuously, so any given volume first increases, and then decreases. An increase creates a vacuum. This vacuum creates suction, and hence, this part of the cycle is where the inlet is located. As a volume decreases compression occurs. During this compression period, fluids can be pumped, or, if they are gaseous fluids, compressed.

Cool so then it would seem our oil pumps do indeed push as well as pull......or to put it naughtily, they suck and blow. LOL

 

[RustyRatRod]

It wasn’t Tim Melling (don’t even know if there is. Tim Melling...I just don’t know) it is Tim Foster and he says what I already know.

An oil pump can not suck a pan dry unless the total leaks in the system are greater than the supply in the sump.

You can bolt on a pump with 100% more volume and the oil flow through the engine is the same. You may get more oil to the system sooner, and the system pressure my be higher (depends on the relief valve spring rate, although you can override the valve and spring) but you will not force more oil through the system. Oil will not compress.

I've argued for years and a lot right here on this forum that pans cannot be sucked dry, but been argued into the ground.

 

[yellow rose]

But when you put more pressure into a system of leaks, there will be more leakage. Nothing needs to be compressed, as long as there are leaks for the oil to flow through.

If you are able to suck 1GPM, and force 1GPM through those leakage paths, your consumption is 1GPM.

But if you can only return .95GPM, you will eventually run out of oil.

Not exactly. Pressure is resistance to flow.

And you are claiming the pan goes dry because oil is retained in the engine. I say there is no way any engine, even a low budget deal will retain all that oil.

So you are mixing two issues together that are not related.

One is a high volume pump making the pan go dry relative to a standard volume pump (who determines what “standard” is) and the engine retaining oil.

They are not the same and not related.

Whatever GPM the engine uses with a (for example and easy math) 10 GPM pump, it will use the same GPM with a 12.5 GPM pump, which is a 25% increase.

 

[justinp61]

Not exactly. Pressure is resistance to flow.

And you are claiming the pan goes dry because oil is retained in the engine. I say there is no way any engine, even a low budget deal will retain all that oil.

So you are mixing two issues together that are not related.

One is a high volume pump making the pan go dry relative to a standard volume pump (who determines what “standard” is) and the engine retaining oil.

They are not the same and not related.

Whatever GPM the engine uses with a (for example and easy math) 10 GPM pump, it will use the same GPM with a 12.5 GPM pump, which is a 25% increase.

But what about pressure? IMO you can't talk about flow (GPM) without referencing pressure. Lets use your example of a 10 GPM and 12.5 GPM pump. If both pumps open the relief valve at the same pressure (60 psi) and assuming the engine can only use, lets say 9 GPM at that pressure (60 psi), then yes the engine will use the same volume of oil.

Now lets take a pump capable of flowing the same 12.5 GPM but at 75 psi. The engines oil requirement is the same but you have changed the pressure. Will the pump move more oil? IMO yes, if the restriction in the engine is enough that it will reach max pressure set by the relief spring. The engine in this example only
requires 9 gpm at 60 psi and we have a pump capable of moving 12.5 gpm at 75
psi.

It's a complex problem and no two engines will be exactly the same.

 

[autoxcuda]

Yes, he covered that and spent some time discussing the new crank driven pumps and their drawbacks.

It was a MUCH better webinar than I expected.

Which pump designs are most efficient?

Which impeller lobe design? how many lobes?

 

[RustyRatRod]

Which pump designs are most efficient?

Which impeller loves design? how many lobes?

You forgot how many molecules and atoms in each pump.

 

[gregcon]

"Whatever GPM the engine uses with a (for example and easy math) 10 GPM pump, it will use the same GPM with a 12.5 GPM pump, which is a 25% increase."

This simply isn't correct in the real world, because it's too simple a statement. It ignores pressure, and it presumes the 10GPM pump was able to keep up with the demands of the engine in the first place.

The engine is built with an 'engineered' system. The pump and pickup are matched to the sump capacity and engine demand. Not always well matched, but nonetheless it's a system. When you go in and make one change to the system - such as a HV/HP pump, you can well upset the balance. The pump can now suck more, and the pan needs to have the capacity to support that sucking.

We can further see evidence of all this when the old trick of adding a quart of oil 'above full' stops the sucking dry problems. By adding sump capacity, we've alleviated the dry pan situation just enough to allow the pickup to stay covered.


I define a 'standard' pump as the pump that was used on the engine originally and (I guess) was engineered as part of a system.

 

[yellow rose]

"Whatever GPM the engine uses with a (for example and easy math) 10 GPM pump, it will use the same GPM with a 12.5 GPM pump, which is a 25% increase."

This simply isn't correct in the real world, because it's too simple a statement. It ignores pressure, and it presumes the 10GPM pump was able to keep up with the demands of the engine in the first place.

The engine is built with an 'engineered' system. The pump and pickup are matched to the sump capacity and engine demand. Not always well matched, but nonetheless it's a system. When you go in and make one change to the system - such as a HV/HP pump, you can well upset the balance. The pump can now suck more, and the pan needs to have the capacity to support that sucking.

We can further see evidence of all this when the old trick of adding a quart of oil 'above full' stops the sucking dry problems. By adding sump capacity, we've alleviated the dry pan situation just enough to allow the pickup to stay covered.


I define a 'standard' pump as the pump that was used on the engine originally and (I guess) was engineered as part of a system.

I agree with all of this and what Justin said in post 91. Im not disagreeing at all.

I know that when I sit down and figure out what I need for an oiling system, I figure pressure into it as well. At one point I was carrying 100 plus PSI and it made more power. That was with the same pump. I had an external bypass that was adjustable and on the dyno I kept increasing the pressure until the power went down.

And on that system I had blocked the bypass in the pump and used a line off the bypass to put the oil back in the pan in front of a baffle so it didn’t blow return oil back across the pickup and uncover it.

So yes, pressure goes hand in hand with flow, until the pump is producing enough flow to the point where the flow and pressure stays the same because the the system can’t use anymore oil and the bypass opens.

I hope that made sense. In my head it does, but when I read it back I’m it so sure.

The best example of this is using full groove mains and a standard volume pump. You will have lower oil pressure at idle because the rods are getting oil all the time. And that adds to the leaks at the rods.

So the standard volume pump doesn’t produce enough oil at idle and slower engine speeds to produce the same oil pressure because of the added flow loss to the rods.

At some point the standard volume pump will produce enough oil flow to open the bypass and that is the pressure maximum. Any more RPM (flow) increases don’t change the pressure because the bypass is open.

Take that same engine, with the same bypass relief pressure and add a high volume pump. The oil pressure will increase at idle and lower RPM because the pump is producing more oil at the same RPM because the rotors are taller, which equals more displacement.

At some point (earlier in RPM because the pump produces more flow at any given RPM with the HV pump verses the standard volume pump) the pump will produce enough oil that the system restricts flow to the point the pressure rises, until the relief opens and the pressure should stay the same regardless of RPM increase, again unless the bypass can’t flow enough and the pressure increases.

I guess IOW’s, the HV pump has more flow at a lower RPM than a standard pump so even with all the same parts and leaks the HV pump has more volume, thus more resistant and more pressure on the gauge until the bypass opens.

This is why I always say to use a HV pump on ANY Chrysler engine using full groove mains, or a solid roller cam with Chrysler oiling and a groove around the cam bearing(s) that feed the heads, because that extra system leakage requires more oil. And if you don’t give it the system suffers. And that’s usually at the end of the feed line. Which is the rockers.

You can have 20 pounds on the gauge and zero at the rockers (tested that). So I don’t like to see anything less than 40 at idle to keep oil flow to the rockers adequate. Unless it is bone stock or close to it.

As to adding oil and keeping the pressure up...that includes many other things.

One is application. On an OE engine, an extra quart of oil in each engine is burning money to the bean counters, so they are built with the lowest oil pan volume the engineers can slide by the nerds. Once you start to make changes to the engine AND/OR chassis, that pan becomes an issue. Increase the RPM and the engine WILL hold more oil.

So the issue isn’t the engine holding more oil, it’s the pan is wrong for the application. A stock pan is pretty much useless on anything but a stock engine. Start modifying the engine, use a bigger pan.

Since oil retention does go up with RPM, pan design, volume and windage trays and crank scrapers become much more important.

There are people running 4 or 5 quart systems on stuff shifting at 8k or more. But the pan is designed to do that, and they have trays and scrapers and baffling that would boggle the mind. And vacuum pumps. All that stuff matters.

Another factor that needs to be looked at is pickup to pan placement.

I can’t tell you how many Chrysler guys using a stock pans listen to the Chevy morons and put the stock pickup .250-.375 off the pan! That pan and pickup was designed to have an SLIGHT interference fit to the pan.

If you need a 1/2 inch impact to pull the pan down to the block you have too much interference. If you move the pickup away from the pan, it can’t pull the oil out of the pan and it will leave a quart or more in the pan. So you add a quart or two to make up for bad engine building.

Again, that is not a pump issue. That’s a pan issue.

Any engine running full groove mains and a stock pan is asking for trouble. The increased oil flow demand makes that stock pan questionable at best.

So I get what you’re saying about times when adding a quart of oil fixes an issue. I’m saying that’s not a pump problem, but a pan problem.

No serious engine should be built without adding capacity to the pan.

A stock pan is 4 quarts. A 6 quart pan is a 50% increase in pan volume. That’s huge. An 8 quart pan is a 100% increase in pan volume.

Increasing RPM or oil volume through the engine or both means you need more pan volume. If you don’t give the pan more volume, the first thing that suffers is the rockers. Run the RPM and the bearings will show you how pissed off they are.

 

[yellow rose]

Which pump designs are most efficient?

Which impeller lobe design? how many lobes?

LOL...he did cover that, but I need to listen to it again and take notes this time. I can’t remember exactly what he said about pump design but he covered it.

 

[mygasser]

Not true, how does the oil get from the pan to the pump? It is not a positive displacement pump. You can’t reach in a bucket and pick up oil with your hand no more than you can water. They don’t have enough surface tension. It is not gravity fed.

the oil is sucked from the pan as it is a positive displacement pump. here's one of many simple explanations readily available online Oil Pumps
as opposed to how a centrifugal pump works https://www.dultmeier.com/technical-library/how-does-a-centrifugal-pump-work.php
neil.

 

[92b]

"Whatever GPM the engine uses with a (for example and easy math) 10 GPM pump, it will use the same GPM with a 12.5 GPM pump, which is a 25% increase."

This simply isn't correct in the real world, because it's too simple a statement. It ignores pressure, and it presumes the 10GPM pump was able to keep up with the demands of the engine in the first place.

The engine is built with an 'engineered' system. The pump and pickup are matched to the sump capacity and engine demand. Not always well matched, but nonetheless it's a system. When you go in and make one change to the system - such as a HV/HP pump, you can well upset the balance. The pump can now suck more, and the pan needs to have the capacity to support that sucking.

We can further see evidence of all this when the old trick of adding a quart of oil 'above full' stops the sucking dry problems. By adding sump capacity, we've alleviated the dry pan situation just enough to allow the pickup to stay covered.


I define a 'standard' pump as the pump that was used on the engine originally and (I guess) was engineered as part of a system.

Here's another way to look at the oil system and the pan being "sucked dry".
If there is no oil available at the pickup tube there will be no oil flow. It doesn't matter how much oil the pump has the capacity to flow or how much resistance to flow the engine provides there must be oil available to the pump.
Can the pan be sucked dry? I'm not sure thats the right question. Can the pick up tube become uncovered? Yes.
I think what's being discussed are oil flow problems and there not happening idling in park. Oil demand changes in an engine when rpm changes and oil supply is affected by how we use the vehicle. From drag racing to rock climbing to circle track to road racing etc. We have to keep the pickup tube covered up with oil. Just look at the extreme measures that are taken in pan design , baffles, trap doors, oil capacity and etc. to accomplish this. So to answer the question "Can a pan be sucked dry?" I don't know. Can a pickup tube get uncovered? Yes, happens all the time. Is that cavitation? I don't know.

 

[gregcon]

I think the term 'sucked dry' is just another way of saying the pickup tube is uncovered.

The real miracle of these oiling systems is that they work as well as they do.

 

[yellow rose]

I think the term 'sucked dry' is just another way of saying the pickup tube is uncovered.

The real miracle of these oiling systems is that they work as well as they do.

That’s a FACT! This stuff was never designed to do what we do with it (to it!).

I agree with the pickup getting uncovered. That’s a better way to describe it.

In fact, in 1970 my parents bought a Ford Maverick. It was a “grabber” and I still think it was a cool car.

It had a straight 6 in it. It had two issues, one of which was never fixed.

That was the heater. That damn thing never worked. And the Ford dealer changed out everything. That sucked not having heat. Sucked HARD.

The other was turning in one direction would make the oil light come on. I can’t remember if it was a right or left turn, but it did it almost every turn.

My mom was pissed. She wanted my dad to fix it, but it was under warranty, and he wanted Ford to fix it.

So he took it to the dealer a couple of times, and they changed the sending unit to a higher pressure and called it good. Took the old man about 5 minutes to figure that out, and he gave up on it and was going to wait for the warranty to end and the fix it.

My mom was LIVID. She wanted to choke my dad out, and stomp the Ford people into the dirt.

One morning my mom said get in the car, uncle Pat is meeting us at the Ford dealership. So my my mom, me and my 3 year old brother get in the car and drive to the dealership.

My mom blows into the shop like she has a rocker up her butt. Now that I think about it, it was turning right, because we had to turn right to get into that craphole and the light came on.

So we jump out and she grabs my brother. We storm the service managers office and my mom threw the keys at his head and said “you make the F’ing payments on it until you FIX it” and out we went.

2 days later, it was fixed. The issue? The wrong pickup tube was installed at the factory. It was too short, and the way the pan was made/baffled it would only uncover turning right.

Funny the crap I remember and what I can’t remember. But that was a learning experience.