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.