Motor Oils Cool Your Engine

Barry-Oil

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Your "certainty" is in error for the reasons I already stated.

That tube will never see but a fraction of that heat to start with then being the "cooler"- it will absorb and sink what it does absorb long before it transfers it to the contents. ( that's not even counting any fluid properties, specific heat, transfer coefficient of time or anything else)

The difference is I am an Engineer who does a good bit of heat exchange work in industry and don't need to link hunt to make my point without fully understanding the science represented in the link.
An engineer of/in what?
The list is perhaps then not for you, but the other readers who always demand a reference.
 
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An engineer of/in what?
The list is perhaps then not for you, but the other readers who always demand a reference.

ME specializing in Forensic Engineering, R&D and all tenets of Lubrication, Reliability/Asset Management.

You? "nucular engineering"? ( you sound like someone we know)
 
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924
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A healthy positive displacement oil pump gives the same volumetric flow regardless of viscosity. So you really aren't getting "more flow and more cooling" with a thinner oil viscosity.
So everyone here on this board should believe that the thinner oil flows and cools better theory is a total falacy?
 
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So everyone here on this board should believe that the thinner oil flows and cools better theory is a total falacy?

I think the theory proper needs some rephrasing.

First, 100 gpm is 100 gpm regardless of if I am pumping warm water, slurry at a mine, caramel at a food plant or tar at Oil Sands Canada so "Z"s initial statement on that is correct.

"Better" is a word that's meaningless unless qualified and in this case it isn't so we will remove it.

In heat transfer, viscosity is an important factor but other critical factors are, total heat holding capability of the fluid ( retention and removal), total volume of fluid working to remove the heat, total surface contact area, temp of the fluid entering, how fast heat is removed from the fluid.

This is also not counting the endothermic properties where the fluid itself creates heat during the working process.

These are all the things the design engineer has to figure out when devising things like what type oil, volume, flow, mass of heat sinks, air flow, fins etc. They all have to work together in a circuit to keep a machine operating at design temperature.

So, changing one part of that very long equation "can" add a benefit to a point but it "can" also create a problem and reduce thermal transfer too. ( usually by creating a bottleneck somewhere else)
 
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Other than fuel economy and bearing clearances, I think engineers require thinner oils like 5w-20 because it dissipates heat better, as with any other thinner fluid. It flows a lot better onto all moving parts and recirculates faster to transfer heat to engine coolant, and also flows to the exterior parts of the engine that then radiate the heat into the surrounding air.

Since on a hot engine the oil pump isn't going to be running in bypass mode until high rpm, the oil volume flowing through the engine is not dependant on viscosity. The oil pump displaces a fixed volume per rpm. Also the majority of the engine is operating in full hydrodynamic lubrication.

Moreover, the heat carried away by the oil is largely generated by the oil. In fact, the oil heats the bearings. Lower viscosity oil will generate less heat through shear friction and result in cooler engine parts and less fuel consumption. You can lower viscosity only so much before the risk of extended metal to metal contact during periods of low oil flow rates becomes excessive though.
 

4WD

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16,644
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Since on a hot engine the oil pump isn't going to be running in bypass mode until high rpm, the oil volume flowing through the engine is not dependant on viscosity. The oil pump displaces a fixed volume per rpm. Also the majority of the engine is operating in full hydrodynamic lubrication.

Moreover, the heat carried away by the oil is largely generated by the oil. In fact, the oil heats the bearings. Lower viscosity oil will generate less heat through shear friction and result in cooler engine parts and less fuel consumption. You can lower viscosity only so much before the risk of extended metal to metal contact during periods of low oil flow rates becomes excessive though.
Bearings are a unique pressure and temp regime … but both the GM and Mopar in my driveway have piston cooling jets/coolers … one more job for our favorite motor oils …
 
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My car has those aswell, but the effect seems limited as far as cooling goes.

 
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Isn't oil flow to be considered in areas other than that which is being push by the oil pump?

Yes, no and maybe and in every case its more of a calculated "guesstimate"- here's why.

As stated many times here, any person can calculate flow from a PD pump going through a tube and a void area equation and deduce thermal transfer. ( basic heat exchange)- you just got to know the dimensions, expected heat and flow.

Lets call the other "splash and fall" ( or pool and fall) to cover everything from spray, cavities or whatever.

We might reasonably know the total internal surface area ( since we designed it and someone has to cast/machine it) and have a good idea of the overall regional (s) skin temp from the material analysis. (There would be more than one heat region)

What we wont know ( with any degree of accuracy or consistency)

The total volume ( in terms of thickness and "hang time") of the coverage of that area since all non "pipe flows" are random and subject to various influences.

We really wont fully know the absorbed heat/temp of the oil as it hits the area to start transferring heat ( that's critical because a given volume of anything has a peak absorption until either it cant take any more or a change of state starts)

So, those 2 big agglomerates of variables exist in the engine, affect the overall transfer and are real and need to be factored in- nobody disputes that.

Capturing and calculating that data is a little more difficult in reality so we do the best we can then usually add a buffer.
 
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Well, there are 30 others worse than air. 31 out of 289 does still make air more of a insulator than conductor, at least from this list.

I am though rather certain the heat coming off those pipes at near 400F is heating those metal cooler tubes, and the oil inside, especially at a stop light.

Point being though, 40% of ALL motor cooling is via the oil. Well, up to 40% I presume. Some here seemed to not know that.

Capture.png

Hey EMPIRE! Good to see you created a new account just to rehash this yet again. I'm sure an admin will see you out the door soon.
 
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1,771
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To add as well, the convective heat transfer rate is mostly the same regardless of oil viscosity. It's also largely the same between oil groups I-IV. Some group V glycols, naphthalenes, and esters can have better heat transfer rates largely due to their higher density. Also note that air entrainment must be considered as an oil that's aerated will not transfer heat well regardless of composition or viscosity. Shearing should also be considered.

The heat generated in the bearings is coming from the friction in the bearings mostly. Very little combustion heat makes it to the bearings. NASCAR cup engines ride a fine line in this area as they typically see ~75°F temperature rise in oil temp at bearing exit. Sump temps at ~280°F with bearing temps at ~355°F with a 0w-20 oil.

Most of the engine operates in mixed or boundary lubrication. The bearings are the exception as well as the rings and pistons during peak piston speeds. Given there's sufficient MOFT to maintain full hydrodynamic lubrication in those areas, of course.
 
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2,337
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Yes, no and maybe and in every case its more of a calculated "guesstimate"- here's why.

As stated many times here, any person can calculate flow from a PD pump going through a tube and a void area equation and deduce thermal transfer. ( basic heat exchange)- you just got to know the dimensions, expected heat and flow.

Lets call the other "splash and fall" ( or pool and fall) to cover everything from spray, cavities or whatever.

We might reasonably know the total internal surface area ( since we designed it and someone has to cast/machine it) and have a good idea of the overall regional (s) skin temp from the material analysis. (There would be more than one heat region)

What we wont know ( with any degree of accuracy or consistency)

The total volume ( in terms of thickness and "hang time") of the coverage of that area since all non "pipe flows" are random and subject to various influences.

We really wont fully know the absorbed heat/temp of the oil as it hits the area to start transferring heat ( that's critical because a given volume of anything has a peak absorption until either it cant take any more or a change of state starts)

So, those 2 big agglomerates of variables exist in the engine, affect the overall transfer and are real and need to be factored in- nobody disputes that.

Capturing and calculating that data is a little more difficult in reality so we do the best we can then usually add a buffer.
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.
 
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1,771
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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.

Correct in theory, often not in practice. Also, don't confuse viscosity with surface adhesion.
 
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2,337
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Respectfully they have it backwards then

The first and most distinguishing characteristic of any oil in any tribology regime is to reduce the COF of bodies in motion (lubricate)

Then comes heat transfer ( cooling)

Then washing/cleaning

Sadly, there is a large body of trade literature out there that teaches this also because the term "cooling" is often misleading and misused.
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.
 
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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.

That's your next problem

The heat that's "absorbed" lets say on round 1 (for simplicity sake) has to be removed from the oil to cool it down so it can absorb more otherwise the circulating oil will make it hotter.

Its overly simplistic ( and wrong) to believe velocity alone will achieve some level of heat removal.

The key to heat exchange be it in an engine or a shell/tube or any other configuration is balancing to achieve optimum results in the soak time for the fluid to absorb heat to its potential then the time it takes to remove said heat from the fluid so it can do it again.

In general terms, a sump ( in and of itself) does little to assist in removing heat from the fluid so there is a combination of things working together.
 
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