Common BITOG myths

[John W. Colby]

quote:

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Originally posted by ebaker:
Re #1, the positive displacement oil pump must suck the oil out of the pan. The oil must flow thru the pickup (inlet) screen and tube. Assuming the pump can pull a perfect vacuum, the flow INTO the pump is pushed by atmospheric pressure. This limits the flow. An oil pump can not pump more flow than what comes through the inlet. Atmospheric pressure will push more thin oil through the inlet tube/screen restriction.

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Atmospheric pressure has absolutely nothing to do with it. Nada, zero, zilch, zippo. You can if you desire have a closed loop system where there is simply no air anywhere in the system (not in your engine obviously). The pump pumps the pumps the oil and there is no atmosphere.

My water pump for example is 200' down in the ground and pumps the water 200 feet vertically to the house. No atmospheric pressure anywhere.

If a pump is designed to grab a "bucket" of oil and shove it in a pipe every time the impeller turns, then that is what it will do, barring it grabbing air instead. The impeller may slow down so that it shoves fewer "buckets" / unit of time, but each time it turns, a bucket enters the pipe. IF you can maintain the rpm of the pump, then it will pump the same volume of liquid regardless of viscosity.

That is what the gentleman is saying.

 

[mechtech]

1911 - Wrong on #1. I am absolutely positive that a thinner oil gets to the cam bearings quicker than a thick oil. I had a GTI with an oil pressure sender for the block, and a separate one for the cam. The cam pressure wouldn't read for a long time with 20-50, but almost immediately with 5-30. Owning my own shop for decades has allowed me to observe first hand the oil flow in many engines. A common example would be chevy V8 pushrod engines. No flow for a while with heavy oil [easy to observe under the rocker cover], and right away with thinner oil.
That positive displacement pump may be positive, but only until the lubricant reaches it's first leakage point [bearings].
Why the heck do you have to be so righteous and _issy, when any experienced tech will tell you otherwise?

 

[teamDFL]

quote:

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Originally posted by Pablo:
The backend to #1 is, well, actually you can overcool your oil. Add a dual remote with two bigass filters, an oil cooler (without thermostat), extra big pan, a separate bypass filter.......so maybe the cooling system comes up to temp on a cool day, but the oil stays quite cool.

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Sorry to go

here, but what is too cold for an oil? In this thread there was little consensus on what was too hot. Any consensus on what the actual temperature of oil is for it to be considered too cold?

 

[Colt]

quote:

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Originally posted by teamDFL:

quote:

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Originally posted by Pablo:
The backend to #1 is, well, actually you can overcool your oil. Add a dual remote with two bigass filters, an oil cooler (without thermostat), extra big pan, a separate bypass filter.......so maybe the cooling system comes up to temp on a cool day, but the oil stays quite cool.

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Sorry to go

here, but what is too cold for an oil? In this thread there was little consensus on what was too hot. Any consensus on what the actual temperature of oil is for it to be considered too cold?

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I've heard a 180 degree or higher thermostat helps oil to do it's job properly.

 

[Ignatz]

When I started as a Mechanic in 1972 at the age 19, I was working in a Porsche-Audi shop where most employees had German acents. I remember the owner of the shop telling me the worst customers to deal with were from the local engineering firm, Gilbert's Associates. He could'nt have been more right. Armed with the latest copy of Road and Track their knowlege was superior to any of our factory training.

 

[mechtech]

So because of the bypass valve, internal pump leakage, possible cavitation, and bearing leakage, there is a very real practical difference [at least when cold] of thick and thin oils in an engine, concerning flow.
On paper, bumblebees can't fly, because of their inferior aaerodynamics.

 

[satterfi]

Ignatz, mechtech and others

I left school with my piece of paper saying I was an ‘Engineer’. The education had only begun. Reality is nothing like what the text books lead one to believe.

It’s kind of funny, but I’m not laughing.

 

[LarryL]

There is something else to consider in all this. Where are you taking the oil and water temp readings. Coolant is not anything close to constant through an engine block and head. An engine can have a normal reading near the thermostat where many temp senders are located and be way over temp in areas around exhaust valves in the head or the back of the block. Sometimes the location of a water temp sender is chosen because it needs a place that does not cavitate. Water makes for a good reading, steam or air does not. Then a gauge is calibrated to read normal when the area indicates the overall temp is okay. In our racing engine programs we take water temps and pressures at different locations to make sure we understand what is going on.

Oil temps vary in the same way and temperature in the pan is just that, in the pan. The temp at the main bearings, camshafts and other places can be all over the place. So when you say you have a certain oil temp, it matters where that temp was taken.

 

[Stinky Peterson]

Well even if you have a positive displacement pump oil has to get to it. It isn't positive suck, it's only positive push. The pump creates negative pressure and the oil flows to it, if the oil is thick like grease then it takes time to move, even though the pump it setting in oil. Another thing - almost all oil pump relief valves can dump the total flow of the pump if necessary.

It's obvious that you don't have any practical experience with equipment operating in cold climates or at least not hydraulic systems.

 

[427Z06]

1911, your original statements are true in a general sense. However, as soon as you look at a real world application and take in consideration all the variables involved, you'll have exceptions or mitigating circumstances induced by other parts of the system. And as you discovered, BITOG members will collectively find everyone of those variables.

 

[427Z06]

quote:

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Originally posted by Ignatz:
Armed with the latest copy of Road and Track their knowlege was superior to any of our factory training.

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Let's put the shoe on the other foot. You mean to tell me you never had a mechanic or a service manager try to bullsheet you?

If Porche mechanics/service managers are this honest and all knowing, I'm guessing it's then worth the price of admission to be a member of that club.

 

[AEHaas]

There are automotive mechanics that are more intelligent than the average doctor. Automotive sciences are becoming increasingly complex.

Unfortunately there are many mechanics in high places that have knowledge but are not keeping up with developments.

My litmus test is to ask several questions to any mechanic that may come in contact with my car(s).

I say "my manual says to use a 5w30, should I use a 20W-50 since we are in Florida?" "I want more power. If I take off my rear mufflers will a get a few more BHP? Will there be any scavenging effects?"

Most of the time I can tell from the answers that "Houston, we have a problem."

We trust our mechanics as we trust our doctors. But are they really up to date??

aehaas

 

[XS650]

quote:

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Originally posted by AEHaas:


We trust our mechanics as we trust our doctors. But are they really up to date??

aehaas

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You're assuming a lot there. Doctors are hghly educated mechanics with the advantage of being able to take credit for patients that get well from natural causes.

Neither one should be trusted until they have earned your trust. Then one should still remain an informed user of their services.

 

[JDP]

quote:

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Originally posted by Ignatz:
When I started as a Mechanic in 1972 at the age 19, I was working in a Porsche-Audi shop where most employees had German acents. I remember the owner of the shop telling me the worst customers to deal with were from the local engineering firm, Gilbert's Associates. He could'nt have been more right. Armed with the latest copy of Road and Track their knowlege was superior to any of our factory training.

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Not sure what your point is by the above statement.

1911's quotes in his previous post were not from "Road and Track".

After reading the original post and the replies that followed, it seems to me that there has been a fair amount of each individuals own ideas added in to change the original circumstances that were described.

What I see 1911 saying is this:

The total volume leaving the outlet of the pump will be the same for each revolution. This is the “displacement” of the pump. It is independent of the pump RPM as the one rotation could be accomplished in 1/1000 sec or 1000 years. Therefore, the material will be moved the same distance thru a line of the same diameter for each revolution no matter what material is used.

The amount of flow is based on the RPM and the displacement but dependent to a small amount, on viscosity (temperature) and the pressure existing at the outlet of the pump.

As has already been stated, the flow produced by a pump is nearly flat for a given RPM within the rated pressure range for that pump when new. This is due to the small design clearances and the pressure imbalance between the inlet and outlet of the pump that further reduces these clearances during operation. The rated flow for a pump is often slightly less than the flow that can be calculated based on the displacement and RPM of the pump. This is because of the secondary flow or slip that is used to cool and lubricate the bearings and other friction surfaces within the pump.

At the pressures used in an engine lubricating system, the actual leakage amounts due to production clearances in the pump should be miniscule when compared to the actual pump flow produced.

References to the “bypass valve” that I know as the pressure regulating valve or relief valve, are not relevant to the situation described.

What happens to the material after it leaves the pumping section does not change the amount that has been produced by the pump in that revolution though it may change the amount of material reaching a significant function.

The dispelling of this “myth” depends on the inlet of the pump being continuously refilled to replace the material previously moved. This would be accomplished by the application of either atmospheric pressure or an artificial air pressure on the surface of the fluid in the reservoir, maintaining a fluid supply in an elevated position above the pump inlet or using a charge pump.

JD

 

[labman]

quote:

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Originally posted by JDP:
snip....

References to the “bypass valve” that I know as the pressure regulating valve or relief valve, are not relevant to the situation described.

What happens to the material after it leaves the pumping section does not change the amount that has been produced by the pump in that revolution though it may change the amount of material reaching a significant function.

The dispelling of this “myth” depends on the inlet of the pump being continuously refilled to replace the material previously moved. This would be accomplished by the application of either atmospheric pressure or an artificial air pressure on the surface of the fluid in the reservoir, maintaining a fluid supply in an elevated position above the pump inlet or using a charge pump.

JD

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The bypass or regulating valve is extremely relevant to the original point. PDP's do produce about the same volume as viscosity goes up. The higher viscosity will reduce slippage. However, flow to the engine will be drastically reduced if most of the flow goes out the valve. I hadn't considered the effect of limiting the intake. I would think that as long as the oil is above its pour point, it would be pulled into the intake. Its vapor pressure would be quite low. However, if it happened, it would add to to the lack of flow to the engine.

So his myth #1 demonstrates a lack of knowledge of common features of modern engines and how they work.

As for myths #2 & #3, they are a matter of degree in normal operation. Yes the oil and water will be a little warmer in some parts of the engine in hot weather. After all, the finned, cast aluminum oil pans are not just for looks or to cut costs.

I stand by my original post.

 

[Mitch]

. Armed with the latest copy of Road and Track their knowlege was superior to any of our factory training. [/QB][/QUOTE]
No the worst people I ever dealt with in my auto machine shop days were the guys that worked for Mitchell Manuals.They actually talked just like their books!

 

[JDP]

Labman

quote:

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So his myth #1 demonstrates a lack of knowledge of common features of modern engines and how they work.

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I don't think that is true at all. His initial post simply described the amounts of oil produced in one revolution of the pump. Just because he didn't include the regulating valve in his situation doesn't mean he has no knowledge of the features and how they work.

I agree that the flow to the engine will be less if the bypass valve happens to open due to the high gpm of the pump and the accompanying restriction of the bearings and other lube passages.

The bypass valve was not the point of his post. Nor was the bearing clearances or other factors in engine luberication.

His myth #1 as stated

quote:

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--"Hig viscosity oils flow through the oil lines slower than low viscosity ones (at a give pump speed)".

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is a myth until there is a "leak" available thru a pressure control valve and the passage size is reduced to running clearances at the bearings.

JD

 

[Gary Allan]

quote:

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His myth #1 as stated

quote: --"Hig viscosity oils flow through the oil lines slower than low viscosity ones (at a give pump speed)".

is a myth until there is a "leak" available thru a pressure control valve and the passage size is reduced to running clearances at the bearings.

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Yes, I agree. The "common" consensus is that (as I would rather state it) lighter oils flow faster than heavier oils. The reality (in 99 out of 100 - a # I pulled out of my arse) is that lighter oils flow easier

Naturally you can have aunt Mary living in Frostbite Falls, ND (Hey, Rocky! Want to see my pull a piano out of my nose?)running 70 weight in her Geo Metro that can shatter that assertion ..but for the vast majority of the conditions encountered ..by the vast majority of users ..the assumption is a "myth" unless qualified. It is more "untrue" than it is "true".