spec that measures ability of oil to cool an engin

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Is there a spec out there that measures the ability of an oil to cool an engine? Or is this just one of the generic jobs that oil does, that folks can't really measure?

Since I've put a full synthetic, and now a synthetic blend, in my Civic, I've noticed that the fan doesn't run loudly every time I idle at an intersection, and I'm wondering if this is something that has been tested/measured.
 
Originally Posted By: DoubleWasp
Might be barking up the wrong tree. Reduction of friction related heating may be what you are experiencing, if anything to do with the oil at all.


Barking up the wrong tree is entirely possible, that's why I asked here.

You think it might simply be a matter of coolant running low--or something else non-oil related?
 
Last edited:
Originally Posted By: paulri


You think it might simply be a matter of coolant running low--or something else non-oil related?


Now that I think about it, I'm pretty sure that low coolant wasn't the (only) issue causing the heating before. If I was running low on coolant, I know I didn't fill it until several months after my synthetic oil change, so even if low coolant was making it heat up, then still, the synthetic was having my engine run cooler.
 
Paulri, your car isn't oil-cooled, it's water-cooled.

Yes, the oil will help dissipate some of the engine's heat, but it's not huge.
 
I noticed water temperature differences with different oils. Pretty significant temp différences, like you are experiencing, enough to stay under or over the fan threshold.
 
Originally Posted By: Popsy
I noticed water temperature differences with different oils. Pretty significant temp différences, like you are experiencing, enough to stay under or over the fan threshold.


Well this one I don't get. Total heat being rejected is one thing but temperature is another. The temperature should be controlled by the thermostat. The temperature is always be controlled within the hysteresis of the device unless you are well over or under the range - which is not the case at steady-state operation.

This is a well worn subject here on BITOG when people claim that an additive causes their engine to operate at a lower temperature. The question then becomes, how did the additive change the set point of the thermostat?
 
Originally Posted By: dparm
Paulri, your car isn't oil-cooled, it's water-cooled.

Yes, the oil will help dissipate some of the engine's heat, but it's not huge.


Then the change would be most likely due to friction? As I said above, I don't think this was an issue with coolant.
 
Originally Posted By: dparm
Paulri, your car isn't oil-cooled, it's water-cooled.

Yes, the oil will help dissipate some of the engine's heat, but it's not huge.


No, and it has to be rejected somewhere and that surface area is fixed. But he's suggesting that the coefficient of friction is significantly lower and as a result the total heat load is less.

I don't think a severely hydrocracked Group III+ oil is going to have a lower coefficient of friction but maybe a predominantly PAO oil does.
 
Originally Posted By: kschachn


Well this one I don't get. Total heat being rejected is one thing but temperature is another. The temperature should be controlled by the thermostat. The temperature is always be controlled within the hysteresis of the thermostat unless you are well over or under the range - which is not the case at steady-state operation.


Only related to friction I think. Simply, with 10W60 I had the fan on all the time, with 0W40 The fan isn't running. Conclusion ; 10W60 does not suit my car since I don't track it (lol), and I probably need a new radiator (unrelated).
 
Originally Posted By: dparm
Paulri, your car isn't oil-cooled, it's water-cooled.

Yes, the oil will help dissipate some of the engine's heat, but it's not huge.


but the amount of heat generated by the shearing of the oil can be huge...
 
Originally Posted By: dparm
Paulri, your car isn't oil-cooled, it's water-cooled.

Yes, the oil will help dissipate some of the engine's heat, but it's not huge.

Engines are oil cooled too. When low on oil, engine will overheat -if it doesn't size before that is.
 
Originally Posted By: Jetronic
Originally Posted By: dparm
Paulri, your car isn't oil-cooled, it's water-cooled.

Yes, the oil will help dissipate some of the engine's heat, but it's not huge.


but the amount of heat generated by the shearing of the oil can be huge...


Must be a joke, as it's only true just as an engine runs out of oil and goes boink.

KINEMATIC VISCOSITY AT THE MAX OEM LISTED OIL TEMPERATURE!

That's closely related to the SAE range at 100c and the amount of Moly or Boron Nitride in the oil in combination with the type of base stock (A German Synthoil is best) also makes a very small difference.
 
Originally Posted By: kschachn
...

In my case it isn't the set point of a thermostat (I put a 82° thermostat, consider it was always fully opened since the fan threshold is 93° for speed 1) but the temp reached by water when operated with 10W60 oil vs a thinner oil (or better oil, viscosity maybe isn't the only factor). With 10W60 the cooling capacity of the radiator is not sufficient, so the calculator turns the fan on. With 0W40, there was less heat generated so the sole cooling capacity of the radiator without fan was sufficient. (Note there is an oil/water exchanger).
Maybe my conclusion is simplist, but I thought thicker than necessary oil = more friction, less lubrication, more heat.
 
I think you are giving the thermostat more credit than it deserves. It does not actually regulate coolant temperature.
It's a very simple device that'll open somewhere near its rated set point and then remain open. It doesn't regulate coolant temperature beyond allowing for faster coolant warm-up.
Beyond the relatively low coolant opening temperature of the thermostat, coolant temperatures can vary widely and it is pretty well accepted that thicker oils will have higher internal friction and will therefore run warmer than thinner ones will.
The engine oil is also a significant source of engine cooling even in liquid cooled engines.
Why else would finned alloy sumps be used on quality cars?
Even my low calorie 318i has one.
 
Originally Posted By: paulri
Is there a spec out there that measures the ability of an oil to cool an engine? Or is this just one of the generic jobs that oil does, that folks can't really measure?

Since I've put a full synthetic, and now a synthetic blend, in my Civic, I've noticed that the fan doesn't run loudly every time I idle at an intersection, and I'm wondering if this is something that has been tested/measured.


There is no specification to determine that.

However, a thermodynamic solution has shown that a pure synthetic base oil (no additives) has a small percentage of improvment over pure mineral oils (no additives) in terms of convective and conductive heat transfer.
 
Originally Posted By: UltrafanUK
Originally Posted By: Jetronic
Originally Posted By: dparm
Paulri, your car isn't oil-cooled, it's water-cooled.

Yes, the oil will help dissipate some of the engine's heat, but it's not huge.


but the amount of heat generated by the shearing of the oil can be huge...


Must be a joke, as it's only true just as an engine runs out of oil and goes boink.


Nah, it's not a joke.

The amount of heat generated inside an engine due to the shearing of the oil film is of the order of whole KW, and a few of them.

For example, the oil film in the big end is going to be some tens of degrees C hotter than the big end, which is some tens of degrees hotter than the oil supply temperature...due to the shearing action in the oil film.

Rather than "carrying away" heat, they are generating their own heat, heat that then gets carried away by the oil flying out, or conducted from the big end to the main, and to the coolant.

Piston skirts waste significant amounts of energy, straight into the coolant basically...OTR designers are looking at thermal barrier coatings to run the liners hotter mid stroke and thin the oil out locally.

The economy benefits of thinner oil are due to less wasted energy...energy that is turned into heat. If there's a reduction in temperature, it's because of this reduction in frictional heating, not because thinner oil "flows" and caries heat away as many think.
 
Maybe flash point can correlate sometimes to hear dissipation.

I guess we should know: the heat capacity of the fluid....how much it can hold before deteriorating or burning-off.


2) the rate at which the fluid absorbs the heat. Like I can burn a piece of bread on the stove faster than I can boil water. Like you dont want to drive hard on a cold engine.....it needs to accept the heat and it can take time.

3) how well it can hold/carry the het in suspension

4) how it can pass-off/relay that heat to something else when given opportunity(s).
 
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