Heat absorption

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190
Location
Cincinnati, OH
Did you ever have a "Zen Like" experience working on your car? Where you don't drop anything and every socket you pick up fits the nut the first time? Well after a great morning of auto maintenance a question popped into my head. What oil is best at absorbing heat? Is there a way to test this? Possibly heat up some oil and measure the oil temperature compared to the temperature of the heating surface to determine the heat transfer? I hope you guys don't think I'm nuts, but what the heck.
 

pbm

Messages
8,884
Location
New York
quote:
Originally posted by mechtech: Thinner oils transfer heat better than thick oils.
Transfer the heat to where? This has always been my concern with running 5w20 in the heat of summer. Are you saying that the thinner oil will dissipate the heat better than say a 10w30?
 

Dagwood

Thread starter
Messages
190
Location
Cincinnati, OH
I was just asking if different oils have different thermal dynamic characteristics. When I was changing my oil I noticed that my 4runnner is equipped with a small oil cooler. I thought that if some oils conduct heat better than others, that would be valuable to know. I was just wondering if there has been any testing or how important this characteristic really is. Do you think that thicker oils hold heat longer than thinner oils? Do thinner oils conduct heat faster, but don't retain heat as long? Are there differences between brands? Some claim that synthetics result in cooler running engines. (kind of a hard one to measure since the thermostat regulates the temperature) Do synthetics transfer heat better or do they reduce friction better resulting in lower heat production?
 
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2,338
Location
Charlotte Metro area
I'm not so sure that the viscosity of an oil is significantly related to it's ability to absorb, or adsorb heat. HOWEVER, the faster a fluid moves, the more potential it has to transfer heat to another area. Then, at some point, increased flow rate can be excessive, because of a shortened "dwell time", the time the fluid takes to transverse the heat exchanger from inlet to outlet, and it will become less efficient at heat transfer....I'm not so sure that "less efficient" means less total units of heat transferred, it just means there is greater and greater work done per unit heat transferred. So, the answer is: it depends. It depends heavily on the flow rate of the fluid, the size, site, and configuration of the heat exchanger. At 250 degrees, the difference in viscosity between an 8 cst and a 12 cst viscosity may be significant enough to show a difference in heat transfer in an engine...again, it depends on the total picture.
 
Messages
2,233
Location
Wisconsin
It is often said that synthetic motor oils have better fluid flow properties due to a more uniform molecular size. This is an aide to cooling. A 5W-20 motor oil will both take on heat faster, from the piston bottoms, and give it up faster, to the crankcase walls or oil cooler coils, than a thicker motor oil. How much is a debatable point & depends on the engine design & driving cycles. We had a thread, sometime during the last year, where the oil temperature data points were logged & graphed. Was it Zoom-zoom ? Anyway, quite interesting, I'll see if i can find it. [Smile]
 
Messages
2,364
Location
sebring, florida
i have some reasonably solid evidence that thicker or thinner oils, as well as dino and synthetic, do not change the operating tempature to any measurable degree. i have a 5hp honda gc160 ohc pressure cleaner and i use it frequently for semi commercal purposes. while i fully realise that this engine is not an automotive engine, it is aircooled and is at the mercy of the elements, so there is no thermostat to regulate the cooling tempature. the engine just runs as hot as it gets. i also run the pressure cleaner under a steady state at around 3400 rpm. i awalys run it in the same manner so the results are reproducable. i also have an infrafred digital tempature gun that i use to monitor the hondas oil tempature as well as cylinder tempature. i have tried various oils in the engine, from 15w50 diesel oils wuch as rotella and delo, to synthetics like german castrol and mobil1 to dino car oils like supertech 10w30, gtx sae40, gtx 20w50, and some blends of leftover oils put together into random mixes. what i found basically is that all of these oils make the engine operate at the same tempature. there is no difference in operating tempature on the cylinder head, or the oil drain plug between any of the oils. which is where i normally point the little laser beam that comes off my tempature gun. the oil drain plug is 1 spot, and one of the cylinder head fins is another spot. actually, running the pressure cleaner in the shade lowers its temp by about 15 degrees. running it when its 70 degrees outside lowers its temp by 10 degrees compared to running it when its 80 outside. so taking into account the difference between shade and ambient temp, the oils do not change its operating temp. which seems to be around 180 at the drain plug, and 240 on the intake side of the cylinder head when its 85 outside. it gets to almost 300 on the exhaust side at an 85 ambient temp. maybe in theoretical labratory conditions a thinner oil or a synthetic might have more potential to transfer more heat from the piston to the cylinder, or to the block, but in real world conditions, the results are so small that i was not able to measure them. i have also casually tried this with my cars and got the same results as the pressure cleaner. weither its dino, synthtic, thick or thin, the oil drain plug is at roughly the same tempature. the ambient temp and weither or not the car is in the sun or shade is the only thing that really makes a difference.
 
Messages
2,233
Location
Wisconsin
This is zoomzoom's thread with a oil temperature comparison of GC 0W-30 vs. a 15W-40 in his turbo. http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=1;t=011178;p=6 The final data summary, listed on page 6, indicates that the GC ran cooler, but I know some here will try to argue that point. This was another good discussion on the topic: http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=011178;p=3#000058 Also some very good comments: http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=011536;p=2#000036 Somebody used a data logger & graphing software to generate some very impressive oil temperature graphs, but I can't seem to find it. [I dont know]
 
Messages
4,478
Location
Southern California
quote:
Originally posted by pbm:
quote:
Originally posted by mechtech: Thinner oils transfer heat better than thick oils.
Transfer the heat to where?

The atmosphere. (The oil pan is subject to the air stream generated by a moving vehicle.)
 
Messages
1,268
Location
SoCal, CA USA
Well, on the face of it, I could buy that an oil that moves around more quickly is also moving heat to other places which can dissipate it better than if it's concentrated in one smaller area. It may very well not be measurable unless you place thermocouples in strategic places and measure them under proper test conditions. It certianly does not sound as much like voodoo as some things around here... Scott
 
Messages
267
Location
Idaho
quote:
Originally posted by Ray H:
quote:
Originally posted by pbm:
quote:
Originally posted by mechtech: Thinner oils transfer heat better than thick oils.
Transfer the heat to where?

The atmosphere. (The oil pan is subject to the air stream generated by a moving vehicle.)

Yup. Ultimately all car engines are air-cooled. The second law of thermodynamics (loosely translated) tells us that heat always travels from a hot place to a cold place. How fast it travels depends on how good the material in question conducts heat. We know that different alloys of steel conduct heat at differnt rates. It seems likely that different formulations of oil would have varying thermal conductivity as well. Someone has probably earned a PhD on this very subject. I do suspect that any oils suitable for automotive use will be pretty close though. Joe
 
Messages
39,805
Location
Pottstown, PA
quote:
Well, on the face of it, I could buy that an oil that moves around more quickly is also moving heat to other places which can dissipate it better than if it's concentrated in one smaller area.
Think about it a minute, Scott. Unless gravity is higher for lighter oils ..they're all pumping at the same rate (assumed operating temps). There's no "faster" about it unless you're talking sloshing around in the pan [I dont know] (visions of the Mobil washing machine "O" logo advertisement cleaning fuel campain).
 
Messages
1,268
Location
SoCal, CA USA
I guess I incorrectly assumed thinner oil (less viscous) would make it's way around the engine faster...not just "drop" to the bottom (pan) Dunno. Doesn't matter really, I will change my oil enough as well as other fluids to make sure it's running as cool as it can anyway. Scott
 
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