Motor Oils Cool Your Engine

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10
Did you know that your motor oil is responsible for approx 40% of total engine cooling?

From Kevin Ferrick (Director, GIS Product Programs, API.ORG)
Many people assume that engine cooling is accomplished only through the action of the water-antifreeze mixture used in the cooling system. In fact, this mixture does only about 60 percent of the cooling job. It cools several engine parts—the cylinder heads, the cylinder walls, and the valves. The crankshaft, the main and connecting rod bearings, the camshaft and its bearings, the timing gears, the pistons, the turbocharger, and many other components of the engine rely directly on the motor oil for cooling. All of these parts have finite temperature limits that must not be exceeded. Some can tolerate fairly high temperatures while others, such as the bearings, must run relatively cool to avoid failure. An ample supply of cool oil must be delivered to the parts, where the oil picks up the heat from the parts, carries it back to the crankcase, and transfers it to the surrounding air.

Some idea of the temperatures an oil experiences may be helpful in understanding the role of oil as a coolant. Combustion temperatures are 1093–1649°C (2000–3000°F. Certain parts of the valves may reach temperatures of 538–1093°C (1000–2000°F). Piston temperatures can reach 538°C (1000°F), and this heat travels down the connecting rods to the rod bearings. Tin and lead, which are the more sensitive of the metals commonly used in bearings, become very soft around 177°C (350°F). Tin melts at 232°C (450°F), while lead will melt at 327°C (620°F). After warmup, crankcase oil temperatures reach 93–135°C (200–275°F), and oil is supplied to the bearings at this temperature. The oil picks up heat at the bearings and leaves them at temperatures around 121–149°C (250–300°F), well below the critical temperatures of bearing failure. The continual cooling of the oil by recirculation to the crankcase is essential to maximizing bearing life.

To keep this cooling process working, the engine must constantly circulate large volumes of oil to the bearings and other engine parts. If the oil supply is interrupted, either by deposit formation, oil pump problems, or low crankcase oil levels, for example, the bearings and other parts can heat up rapidly from increased friction and combustion temperatures or decreased cooling by the oil. A bearing failure is often referred to as a “burned-out bearing” because temperatures rose high enough to actually melt the bearing metal.

While only a small quantity of oil is required at any one time and any one place to provide lubrication, the oil pump must circulate many gallons of oil per minute in order to achieve lubrication and properly cool these parts. Chemical additives and the physical properties of the oil have little effect on its ability to provide adequate cooling. What is critical is the continuous circulation of large volumes of oil throughout the engine and over hot engine parts. This is made possible through the use of an oil of the right viscosity for that engine, high-volume oil pumps, and oil passages adequate to handle the required volume of oil. These oil passages cannot do the job properly if they are allowed to become partially or completely clogged with deposits. When this happens, the oil cannot circulate or cool properly, and early engine failure may result. This is yet another reason for using the proper performance oil and for changing the oil before the contaminant level becomes too high. Proper cooling also requires that the oil level in the crankcase never be permitted to remain below the “add oil” line on the dipstick.
 
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2,815
Location
Kentucky
The oil is the closest fluid to the source of the heat-- literally on the parts instead of inside a coolant jacket. So indeed it would make sense that oil would be responsible for a good portion of the engine cooling. The engine block / cylinder head acts as a giant heatsink which helps transfer heat from the oil to the coolant.
 
Messages
169
Location
Arizona
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.
 
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2,337
Location
South Carolina
I have had this discussion/argument over decades with mechanics and car enthusiasts.
What I learned, many years ago, in Cat Engine diesel school was an oils properties (in order):
1. Cool engine parts
2. Lubricate
3. Keep the engine clean and free of contaminates
We were taught the same when I was trained on the F-16 in the Air Force.
 
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4,238
Location
Kansas
Did you know that your motor oil is responsible for approx 40% of total engine cooling?

From Kevin Ferrick (Director, GIS Product Programs, API.ORG)

Oh really? Learn something new each day. I only fear that it might be higher as cooling system maintenance is often overlooked. I try to do whatever to give my car all the chances to run cooler as possible.
 
Messages
4,238
Location
Kansas
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.
I'm fine with a thinner oil as long as it has the body to hold up. I would use a Redline or Amsoil 5w20 in a Arizona or New Mexico summertime over a standard Grp3 5w20 hands down. We see a lot of recommended oil weight that are higher for the same engine in other regions so I am open to going up a weight from oe if the temperature,driving style and miles on equipment warrant it. In my own application I have ran one of the thickest 0w20 oils know to be as thick as some 5w30 so Im confident that there is some wiggle room.
 
Messages
728
Location
EU
These 40% are no general fact and usually would be a gross exaggeration. Air cooled engines are gone because the oil route cannot easily compensate for not being water cooled. Rotary engines also emphasize the oil route as the rotor sees oil spray on the inside. And modern thermal management etc. may shift things around, but that would be another kind of 40% again. Don't create one more credo from the figure.
 
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17,036
Location
Upper Midwest
I'm fine with a thinner oil as long as it has the body to hold up. I would use a Redline or Amsoil 5w20 in a Arizona or New Mexico summertime over a standard Grp3 5w20 hands down. We see a lot of recommended oil weight that are higher for the same engine in other regions so I am open to going up a weight from oe if the temperature,driving style and miles on equipment warrant it. In my own application I have ran one of the thickest 0w20 oils know to be as thick as some 5w30 so Im confident that there is some wiggle room.
If the oil has more "body" then it isn't exactly thinner is it?
 

OVERKILL

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45,812
Location
Ontario, Canada
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.

The biggest difference happens on a cold start where a 5w-20 will be significantly less viscous than say a 5w-40. This leads to lower pumping losses and lower frictional losses during that warm-up phase and thus a tick better fuel economy. Once the oil is up to operating temperature there is VERY little difference in viscosity (relatively speaking) between the two, so any difference in flow (gravitational) is negligible.
 
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4,531
Location
Ca.
Ive always been taught oil was primarily cooling, and everything else secondarily, but Im old...

On a high perf marine engine you never exhaust the cool water and only have to back out of it for control reasons or escalating oil temps.

Ive seen oil skyrocket from 180 to over 300 in minutes while the water temp stays at 100 degrees.
 
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689
Location
My Mother's basement.
Did you know that your motor oil is responsible for approx 40% of total engine cooling?
From Kevin Ferrick (Director, GIS Product Programs, API.ORG)
In some cases the figure is 100%
custom-suzuki-bandit-600-9.jpg
 

OVERKILL

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45,812
Location
Ontario, Canada
Is there?

Yes.

Let's look at a 5w-20 and 5w-40 as a comparison.

Mobil Super 5w-20 has the following properties:
Visc @ 40C: 47cP
Visc @ 100C: 8.3cP

Mobil 1 Formula M 5w-40 has the following properties:
Visc @ 40C: 79cP
Visc @ 100C: 13.2cP

Let's assume a typical start-up temp of 20C.

At 20C:
5w-20: 118cP
5w-40: 200cP

A difference of 82cP

At 100C our difference is only 4.9cP

At 80C our 5w-20 is the same viscosity as our 5w-40 at 100C.

At a higher oil temp, the difference gets even smaller.

At 120C:
5w-20: 5.7cP
5w-40: 8.9cP
Delta: 3.2cP

Of note, at 120C our 5w-40 is now roughly the same visc as our 5w-20 at 100C.
 
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