Motor Oils Cool Your Engine

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Well ok. I've listened to engineers and oil formulators over the years and being an old knuckle dragging diesel mechanic, I'll stick to my beliefs. It reminds me of the argument of what is the most important properties of antifreeze. Does it protect metal from corrosion, boil over or from freezing?
Funny thing is a room full of engineers will rarely agree on a subject. It all falls on what they were taught, read, experienced, etc.

I am not even attempting to sway your belief one way or the other but what I said is a 100% irrefutable fact of the physics of thermal dynamics and the science of tribology and anyone differing from it is simply incorrect. Its not a subject for debate.
 
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Ok but then where does the oil get cooled? The sump is supposed to contain the coolest oil in the engine and that is where the returning oil dissipates it's heat (I proably have that all wrong too).
 
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Ok but then where does the oil get cooled? The sump is supposed to contain the coolest oil in the engine and that is where the returning oil dissipates it's heat (I proably have that all wrong too).

Sure, be happy to help explain this but you have to look at it as a whole for it to make sense.

A good thermal imaging scan of a machine shows this very clearly for the eye to see.

For discussion purposes, lets say an engine generates 1000 units of heat ( just to pick a number that's round)

700 of those units come from the heat of combustion

300 come from the total area where friction is happening ( cylinder walls, pivots on piston pins, valve stems and everything else realizing that the journal bearings should not be contacting but fluid shear is generating some heat too)

Out of all of that heat- some goes out through the exhaust, some radiates from the mass to the skin of the engine, some is removed from the coolant. ( the key here is physically removed from the engine)

That's going to account for say 600-700 units ( lot of variables affecting that)- that's going to be the bulk of generated heat.

Now the oil absorbs its portion ( still in the engine so the engine has yet to be 'cooled)- heat is removed from the skin of the pan and into the air ( while its in aerosol form, thin film and even streams so that's much more surface area and a variable)

Whatever "remains" becomes the "normal operating temperature" of a machine.

its at that point where the way its operated determines the additional properties of the oil, coolant or other transfer means ( external coolers etc.) that need to be added.

Granted this is a simplistic breakdown at 1000 ft. but that's essentially the process and how oil absorbs and removes heat in a machine.

This is why things like varnish ( just like scale in a steam system) affect the heat removal from the oil
 

Barry-Oil

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Ok but then where does the oil get cooled? The sump is supposed to contain the coolest oil in the engine and that is where the returning oil dissipates it's heat (I proably have that all wrong too).
The oil sump is where oil will accumulate and where the heat in the oil is removed to the outside air. And it may be the view of the "engineers" that bearings heat from friction, but most of their rise in temp comes from the heat generated by combustion, about 98% of all the heat comes from combustion. And to boot, near 80% of all friction in engine is from piston rings.

Read all of post #1 again. And beyond "engineer" words on a forum, proof that very little % heat is by friction, simply attach the motor to an electric drive on the crank and remove the spark plugs, spin it at 6k rpm for an hour, measure the oil temp. Repeat same test with plugs but without spark. Lab data tells all most of the time.
 
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2,337
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South Carolina
Sure, be happy to help explain this but you have to look at it as a whole for it to make sense.

A good thermal imaging scan of a machine shows this very clearly for the eye to see.

For discussion purposes, lets say an engine generates 1000 units of heat ( just to pick a number that's round)

700 of those units come from the heat of combustion

300 come from the total area where friction is happening ( cylinder walls, pivots on piston pins, valve stems and everything else realizing that the journal bearings should not be contacting but fluid shear is generating some heat too)

Out of all of that heat- some goes out through the exhaust, some radiates from the mass to the skin of the engine, some is removed from the coolant. ( the key here is physically removed from the engine)

That's going to account for say 600-700 units ( lot of variables affecting that)- that's going to be the bulk of generated heat.

Now the oil absorbs its portion ( still in the engine so the engine has yet to be 'cooled)- heat is removed from the skin of the pan and into the air ( while its in aerosol form, thin film and even streams so that's much more surface area and a variable)

Whatever "remains" becomes the "normal operating temperature" of a machine.

its at that point where the way its operated determines the additional properties of the oil, coolant or other transfer means ( external coolers etc.) that need to be added.

Granted this is a simplistic breakdown at 1000 ft. but that's essentially the process and how oil absorbs and removes heat in a machine.

This is why things like varnish ( just like scale in a steam system) affect the heat removal from the oil
Ok. Thanks!
 

Barry-Oil

Thread starter
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Maybe in "nucular" science but not in this universe



Where is this "lab data"?
Lab data is everywhere. As a tenet of lubes you should know where the data is at, yes?

Just 3% of input energy is converted to heat via friction. 20-25x that is heat from combustion process.
 
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The bearing heat delta in a NASCAR engine is found using a Spintron, a machine that uses an AC motor to spin an engine at a set rpm. The bearing temp rise was 75°F at 8000 rpm using oil that's already heated to 280°F in the sump. Note there is no combustion happening, just friction.
 
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Lab data is everywhere. As a tenet of lubes you should know where the data is at, yes?

Good then produce it. The burden is on you, not me since you are the claimant. ( you did learn that concept in law school didn't you?)

Then explain it in detail.

Just 3% of input energy is converted to heat via friction. 20-25x that is heat from combustion process.

That's both non sequitur to the discussion and a straw man point. Nobody here was discussing "input energy" or analyzing the combustion process.
 
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1,965
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The bearing heat delta in a NASCAR engine is found using a Spintron, a machine that uses an AC motor to spin an engine at a set rpm. The bearing temp rise was 75°F at 8000 rpm using oil that's already heated to 280°F in the sump. Note there is no combustion happening, just friction.

I'm surprised its that high for a journal bearing but I guess at 8 grand its really working the fluid.

I use a similar rig but usually I am artificially radially loading the bearing and most of mine are rolling element types.
 
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This subject has been discussed quite a bit in the past, this was a post by Shannow. Is it correct?

 

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Well all fine and dandy but not considering heat and absorption of heat in oil not within the galleries but lets consider the already heated oil returning to the sump. I would think a thinner oil would return to the sump quicker and, as such, contributing to cooling the engine.

Heat two oils to just 60C and then pour them. Is there a visible difference in how fast they flow? Now consider what it's like at 100C+. Per the data I already posted, the difference in viscosity becomes smaller as the oil heats so at elevated temperatures, which is where your concerns should be focused, the rate of return to the sump is a non-issue. Where that tiny difference in viscosity is relevant is in areas impacted by MOFT.
 
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This subject has been discussed quite a bit in the past, this was a post by Shannow. Is it correct?

If you mean this...
The majority of the heat in the oilis heat generated by the oilitself undergoing shear...not the number of (non)explosions taking place in the cylinder...yes, the (non)explosions make the motive power, but the friction generates most of the heat...

If you mean the information in his post as written and in context with the discussion he was in, he is correct and I referenced the same thing up thread about the shear inside the bearings generating heat.

I think the point of confusion is that the scenario here is not the same one as there and the context is misleading.

Its important when doing thermal transfer ( and most things engineering) to remember that there are specific things that have bookends in themselves and cant be mixed together like in a conversation.

Use the above as an example to illustrate the point...

The heat IN the oil GENERATED by the oil.......- That's a measurement of endothermic heat by the fluid itself as its worked. You need to know that to determine the mass, metallurgy, fluid displacement and add it to the overall cooling need. That's best a cold test spinning an engine with a motor to see exactly what it is isolated.

The oil in the sump is that measurement PLUS (whatever absorbed heat the oil got by conduction via contact - whatever heat it lost to air via convection) + whatever latent heat is still transferring into the oil via the mass of the engine - whatever else is removing heat= "the heat' remaining.

Theres a lot of detail, specificity and differential calculus and ranges of these equations. They are not static or linear and then different designs and different lubrication regimes have different inputs and outputs.

Hope that helped a bit
 
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17,036
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Yes I understand that, I have a BSME and I got straight As in my thermodynamics classes (mainly because I was working for a coal-fired utility during the summers). I was just responding to the notion that "3%" or whatever it was of the heat was generated in the bearings due to shear. The post I referenced shows that the value is much higher. Looking back it was a statement by the troll that was apparently taken out back and shot.
 
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6,425
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All automotive engines are air cooled. Coolant and oil are just mediums for the transfer. Water is a better medium for heat transfer because it is a better conductor of heat than oil. if oil was a great medium for cooling our radiators would be filled with oil.
The engine oils function in the engine is to keep the moving parts apart. It does a better job of this when the oil remains cool enough to maintain MOFT. That is why many engines use coolant to oil exchangers upstream of the bearings in the oil circuit. It provides a greater level of assurance for oil temperature control than the conduction of heat through the oil pan, which can vary widely due to ambient temperature, while a thermostat controlled coolant system is much more predictable And reliable.

apologies for the upper and lower case mixups, I am a lazy with the iPad.
 
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1,965
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All automotive engines are air cooled. Coolant and oil are just mediums for the transfer. Water is a better medium for heat transfer because it is a better conductor of heat than oil. if oil was a great medium for cooling our radiators would be filled with oil.
The engine oils function in the engine is to keep the moving parts apart. It does a better job of this when the oil remains cool enough to maintain MOFT. That is why many engines use coolant to oil exchangers upstream of the bearings in the oil circuit. It provides a greater level of assurance for oil temperature control than the conduction of heat through the oil pan, which can vary widely due to ambient temperature, while a thermostat controlled coolant system is much more predictable And reliable.

apologies for the upper and lower case mixups, I am a lazy with the iPad.

Needs a little more training
 
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And it may be the view of the "engineers" that bearings heat from friction, but most of their rise in temp comes from the heat generated by combustion ...

Not the big end rod and crankshaft journal bearings. The rods are too long to transfer much if any heat from combustion into the rod bearings. All the heat generated in the rod big end and crankshaft journal bearings is simply from the oil shearing in the hydrodynamic wedge.

Read all of post #1 again. And beyond "engineer" words on a forum, proof that very little % heat is by friction, simply attach the motor to an electric drive on the crank and remove the spark plugs, spin it at 6k rpm for an hour, measure the oil temp. Repeat same test with plugs but without spark. Lab data tells all most of the time.

I'd like to see test data from those experiments ... would be interesting, and I'd venture to say the oil would heat up more than most would think just from the friction and oil shearing from the engine "running" without combustion.
 
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