This will probably be the next experiment over on Project Farm.
Synthetic oil worse for cooling?
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Great summary … IMO we have shelves full of semi's sold as synthetic … but they are a great value in the US and other places that give specifications and approvals the front row seats …
This paper might be of interest to some... titled, "Heat Transfer Properties of Engine Oils".
Heat Xfer Properties
Heat Xfer Properties
All, there's a bunch of factors at play in this...specifically as it related specifically to air cooled engines...and I don't think too many of us are running them in our Passenger car motors these days.
Most of the heat in an engine oil is generated from within the oil film(s)...the couple of air cooled papersI've linked to in the past show a much smaller effect from thermal conductivity from the piston etc...by cutting out that path, with small effects...yes squirters intentionally improve that, but that's another small additive to bulk oil temperature, not a primary driver.
Specific heat...the amount of heat that a unit of mass can shift per degree of temperature rise...there's not enough difference to make any difference.
Convective thermal conductivity, how heat gets into oil (assuming it's not generated by shear), and out of oil on sumps and the like...
Really, there's not enough difference to be ANY difference.
Thermal transfer oils are typically mineral (high tempeature)...they have a tiny advantage in heat transfer, but a massive advantage in cost.
Some charts here...
http://www2.eng.cam.ac.uk/~mpfs/papers/articles/WTC2005/pdfs/t-3/WTC2005-64316.pdf
If I had an air cooled passenger vehicle, it would be on synthetic (in whatever that means).
Most of the heat in an engine oil is generated from within the oil film(s)...the couple of air cooled papersI've linked to in the past show a much smaller effect from thermal conductivity from the piston etc...by cutting out that path, with small effects...yes squirters intentionally improve that, but that's another small additive to bulk oil temperature, not a primary driver.
Specific heat...the amount of heat that a unit of mass can shift per degree of temperature rise...there's not enough difference to make any difference.
Convective thermal conductivity, how heat gets into oil (assuming it's not generated by shear), and out of oil on sumps and the like...
Really, there's not enough difference to be ANY difference.
Thermal transfer oils are typically mineral (high tempeature)...they have a tiny advantage in heat transfer, but a massive advantage in cost.
Some charts here...
http://www2.eng.cam.ac.uk/~mpfs/papers/articles/WTC2005/pdfs/t-3/WTC2005-64316.pdf
If I had an air cooled passenger vehicle, it would be on synthetic (in whatever that means).
Originally Posted by Shannow
All, there's a bunch of factors at play in this...specifically as it related specifically to air cooled engines...and I don't think too many of us are running them in our Passenger car motors these days.
Most of the heat in an engine oil is generated from within the oil film(s)...the couple of air cooled papersI've linked to in the past show a much smaller effect from thermal conductivity from the piston etc...by cutting out that path, with small effects...yes squirters intentionally improve that, but that's another small additive to bulk oil temperature, not a primary driver.
Specific heat...the amount of heat that a unit of mass can shift per degree of temperature rise...there's not enough difference to make any difference.
Convective thermal conductivity, how heat gets into oil (assuming it's not generated by shear), and out of oil on sumps and the like...
Really, there's not enough difference to be ANY difference.
Thermal transfer oils are typically mineral (high tempeature)...they have a tiny advantage in heat transfer, but a massive advantage in cost.
Some charts here...
http://www2.eng.cam.ac.uk/~mpfs/papers/articles/WTC2005/pdfs/t-3/WTC2005-64316.pdf
If I had an air cooled passenger vehicle, it would be on synthetic (in whatever that means).
Yeah, that's the same one I found and linked to above. Had to read it a couple times (and still not certain I grasped it fully) but I think the gist of it from what I gathered is exactly as you said, the difference is not significant enough to be particulaly noteworthy. This maybe explains why when you peruse the PDS for htf's the main selling point for synthetics (v. minerals) seems to be it's thermal stability and high(er) heat tolerance and not any advantage in thermal conductivity. Seems there are other, more significant, forces at play that effect the heat transfer efficiency of the system. (like air v. liquid cooling, metal type, flow)
All, there's a bunch of factors at play in this...specifically as it related specifically to air cooled engines...and I don't think too many of us are running them in our Passenger car motors these days.
Most of the heat in an engine oil is generated from within the oil film(s)...the couple of air cooled papersI've linked to in the past show a much smaller effect from thermal conductivity from the piston etc...by cutting out that path, with small effects...yes squirters intentionally improve that, but that's another small additive to bulk oil temperature, not a primary driver.
Specific heat...the amount of heat that a unit of mass can shift per degree of temperature rise...there's not enough difference to make any difference.
Convective thermal conductivity, how heat gets into oil (assuming it's not generated by shear), and out of oil on sumps and the like...
Really, there's not enough difference to be ANY difference.
Thermal transfer oils are typically mineral (high tempeature)...they have a tiny advantage in heat transfer, but a massive advantage in cost.
Some charts here...
http://www2.eng.cam.ac.uk/~mpfs/papers/articles/WTC2005/pdfs/t-3/WTC2005-64316.pdf
If I had an air cooled passenger vehicle, it would be on synthetic (in whatever that means).
Yeah, that's the same one I found and linked to above. Had to read it a couple times (and still not certain I grasped it fully) but I think the gist of it from what I gathered is exactly as you said, the difference is not significant enough to be particulaly noteworthy. This maybe explains why when you peruse the PDS for htf's the main selling point for synthetics (v. minerals) seems to be it's thermal stability and high(er) heat tolerance and not any advantage in thermal conductivity. Seems there are other, more significant, forces at play that effect the heat transfer efficiency of the system. (like air v. liquid cooling, metal type, flow)
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I'm saving this thread. Great information, Mola and Shannow. We need much more of these technical topics on BITOG.
Originally Posted by Shannow
Mola, the heat in a journal bearing is generated within hte bearing, rather than conducted through it the oil film
Right, and assuming equal temperature rise of a higher specific heat oil on its way through a bearing, with other factors constant, makes no sense to me.
Mola, the heat in a journal bearing is generated within hte bearing, rather than conducted through it the oil film
Right, and assuming equal temperature rise of a higher specific heat oil on its way through a bearing, with other factors constant, makes no sense to me.
My thoughts:
-- Since the majority of "full synthetic" oils nowadays are actually highly refined mineral oils, I don't buy it either.
-- Engineers know that air cooled engines run hotter, so typically they call for shorter service intervals to compensate for any increased thermal breakdown of the oil.
-- If you are running a truly synthetic oil (i.e. boutique PAO/Ester oils) and the small difference in thermal abilities between mineral oil and synthetic oil are going to cause significant issues in your engine, you have bigger problems to deal with.
-- Since the majority of "full synthetic" oils nowadays are actually highly refined mineral oils, I don't buy it either.
-- Engineers know that air cooled engines run hotter, so typically they call for shorter service intervals to compensate for any increased thermal breakdown of the oil.
-- If you are running a truly synthetic oil (i.e. boutique PAO/Ester oils) and the small difference in thermal abilities between mineral oil and synthetic oil are going to cause significant issues in your engine, you have bigger problems to deal with.
Originally Posted by talest
Same way people try to say that you can't use synthetic oil in a Rotary (RX-7, RX-8) engine, then consider themselves to have been knowledgeable...
FWIW, you can use whatever you want, but Mazda doesn't recommend it. But they're just engineers.
But do or do not, IDGAF.
Same way people try to say that you can't use synthetic oil in a Rotary (RX-7, RX-8) engine, then consider themselves to have been knowledgeable...
FWIW, you can use whatever you want, but Mazda doesn't recommend it. But they're just engineers.
But do or do not, IDGAF.
MolaKule
Staff member
Originally Posted by Shannow
Mola, the heat in a journal bearing is generated within hte bearing, rather than conducted through it the oil film
I am not sure what you are referring to since you didn't quote a specific sentence, but the temperature rise in a journal bearing is due to a number of factors including 1) the shearing of and pressure peaks in the wedge's oil film and 2) friction due to the time the journal and bearing are in mixed or boundary regime conditions.
Quote
Effect on power loss
Commonly the phenomenon of friction is perceived as an action of rubbing of two solid objects over each other. However in the hydrodynamic bearings there is no direct contact between the bearing and journal surfaces. They are separated with a film of fluid lubricant which is adhered to the both surfaces. As the journal surface moves it produces movement of the lubricant. Velocity of the lubricant is varying in the direction across the film thickness. It has the maximum value at the journal surface and gradually decreases to zero at the bearing surface. The oil film may be presented as having many layers moving relatively to each other. Such motion produces a shear force between the adjacent layers. The force contradicts to the rotation of the journal. This force is called hydrodynamic friction. Hydrodynamic friction causes a loss of power which is converted into heat and dissipated in the lubricant, the engine parts and the ambient atmosphere.
https://www.substech.com/dokuwiki/d...hydrodynamic_friction_of_engine_bearings
Heat from the block is also conducted down to the journal bearing area in terms of thermal energy movement from the combustion chamber down to the lower end.
The movement of lubricating oil in and out of the eccentric wedge is essentially a movement of oil via convection, so it is the convection (fluid movement} of the oil that transfers thermal energy out of the bearing. Temperature rise in the bearing is due to both mixed or boundary regime conditions AND the Conduction of thermal energy from the oil to the journal and bearing surfaces and is dependent upon the oil's dwell time in the wedge. However, the bulk of thermal energy transfer is due to convection (flow) of the oil.
see page 162 of the this reference:
Fundamentals of Fluid Film Journal Bearings and Modeling
Mola, the heat in a journal bearing is generated within hte bearing, rather than conducted through it the oil film
I am not sure what you are referring to since you didn't quote a specific sentence, but the temperature rise in a journal bearing is due to a number of factors including 1) the shearing of and pressure peaks in the wedge's oil film and 2) friction due to the time the journal and bearing are in mixed or boundary regime conditions.
Quote
Effect on power loss
Commonly the phenomenon of friction is perceived as an action of rubbing of two solid objects over each other. However in the hydrodynamic bearings there is no direct contact between the bearing and journal surfaces. They are separated with a film of fluid lubricant which is adhered to the both surfaces. As the journal surface moves it produces movement of the lubricant. Velocity of the lubricant is varying in the direction across the film thickness. It has the maximum value at the journal surface and gradually decreases to zero at the bearing surface. The oil film may be presented as having many layers moving relatively to each other. Such motion produces a shear force between the adjacent layers. The force contradicts to the rotation of the journal. This force is called hydrodynamic friction. Hydrodynamic friction causes a loss of power which is converted into heat and dissipated in the lubricant, the engine parts and the ambient atmosphere.
https://www.substech.com/dokuwiki/d...hydrodynamic_friction_of_engine_bearings
Heat from the block is also conducted down to the journal bearing area in terms of thermal energy movement from the combustion chamber down to the lower end.
The movement of lubricating oil in and out of the eccentric wedge is essentially a movement of oil via convection, so it is the convection (fluid movement} of the oil that transfers thermal energy out of the bearing. Temperature rise in the bearing is due to both mixed or boundary regime conditions AND the Conduction of thermal energy from the oil to the journal and bearing surfaces and is dependent upon the oil's dwell time in the wedge. However, the bulk of thermal energy transfer is due to convection (flow) of the oil.
see page 162 of the this reference:
Fundamentals of Fluid Film Journal Bearings and Modeling
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