What Defines the Cooling Efficiency of Motor Oils?

In summary, a straight oil like SAE30 actually cools better than say a 5w30, reason being is because the multi-grade uses long chained polymers which uncoil as they get hotter which affects the cooling abilty of the oil.
  • #1
Physics_Kid
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hi all. i am trying to formulate some testing of different motor oils. i am looking to document which oils have better cooling properties. i read some info years back that a straight oil like SAE30 actually cools better than say a 5w30, reason being is because the multi-grade uses long chained polymers which uncoil as they get hotter which affects the cooling abilty of the oil.

but before i design my test apparatus i want to get clarity on what makes for a better cooling fluid. the specific heat is one property of a substance, but that alone to me does not define a better cooling fluid. is there a property of fluids that define endothermic and exothermic rates? in other words, if a fluid flows over a metal channel which property of fluids defines which fluid absorbs the most energy given a fixed flow rate of the fluid?

i am thinking my apparatus will be something like this. a rectangular box, ~12" on the long side, ~4" on the short side, and about ~6" tall to hold fluid around 4"-5" high. this "box" is made of 1" thick rigid foam board with a 1/4thick aluminum plate siliconed to one end of the box. on the opposite end will be an immersion heater. i will measure external temp of the aluminum vs time. i am figuring the better cooling fluid will be the one which shows the rate of temp change to be the fastest regardless of what the equilibrium temp is.

does this make sense?
 
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  • #2
Important factors will include be viscosity, specific heat capacity, operating temperature, thermal conductivity and even density.
If you want a good test I think you should consider forced circulation. Not many engines use simple convection cooling - the oil is at least 'splashed' around.
 
  • #3
What's your definition of "better"?

Have a think about the limits of performance. For example water makes a good cooling media under the right conditions but it gives you other problems to solve at temperatures over 100C. What problems does oil have at different temperatures? Is oil being used for other reasons and are they impacted by heat?
 
  • #4
ok,

1) well, i want to see how well the fluid absorbs heat (energy), moves it from one side to the other, and then gives it up to the aluminum heat sink on the other end (similar to the oil in an engine block). do i need to use a circulator for this test? i guess i am testing for thermal conductivity, i cannot find this spec for any motor oil and the makers won't tell me.
2) "better" - i guess my definition is the fluid that acts as the better heat sink.
 
  • #6
ah, thanks much for those links, that helps me quite a bit. however, i do want to compare synthetics.

a few years back i was reading an article about pure water being best for a racing engine (i was investigating those wetter wetter products, etc), in that article it had a snippet on the order of "...and using straight oil grade vs multi-grade also helps cool an engine better".
 
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FAQ: What Defines the Cooling Efficiency of Motor Oils?

1. What are the properties of a good cooling fluid?

A good cooling fluid should have a high thermal conductivity, low viscosity, and high heat capacity. It should also have a low freezing point and a high boiling point to be effective in a wide range of temperatures. Additionally, it should have good stability and compatibility with the materials used in the cooling system.

2. How does a cooling fluid effectively remove heat?

A cooling fluid removes heat through conduction and convection. It absorbs heat from the source and carries it away, either through direct contact or through a heat exchanger. The fluid then releases the heat to the environment, either through natural or forced convection.

3. What types of cooling fluids are commonly used?

Water, ethylene glycol, and propylene glycol are some of the most commonly used cooling fluids. Other options include mineral oils, synthetic oils, and refrigerants such as ammonia and carbon dioxide.

4. How do I choose the right cooling fluid for my application?

The choice of cooling fluid depends on various factors such as the operating temperature range, heat load, compatibility with materials, and cost. It is important to consult with an expert and consider all these factors before making a decision.

5. How can I maintain the effectiveness of my cooling fluid?

Regular maintenance is essential to keep a cooling fluid effective. This includes monitoring its quality and condition, replacing it when necessary, and removing any contaminants that may affect its performance. It is also important to follow the manufacturer's recommendations for proper handling and storage of the fluid.

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