Oil and Water properties

[hotroadking]

Some folks on another board were discussing oil temps in our HD's and the following came up, just wondered if someone here knows the scoop..

The question is "does oil absorb more or less heat energy than water for a corresponding rise in temperature"

Second, would the answer be different when comparing a syn to a dyno 20W-50

 

[wileyE]

If your talking oiljacketed oil cooling (polaris, suzuki,bmw) vs true watercooled. Water is better IMO. They may not run much cooler internal temps but they do so at higher state of tune making more power with tigher clearances.

 

[Titan]

Heat transfer will be mostly differentiated by flow rate. If the oil is thicker than the antifreeze (water) solution, the antifreeze solution has the inherent advantage of potentially higher flow rate. Of course, flow rates and heat production must be optimized to take advantage of the differences.

It is for this reason (higher flows), that many people see lower oil temperatures in their engines when using lower viscosity oils. Too many non-water-cooled engine operators get stuck in the idea that: "if thick is good for my engine, thickER must be better". It isn't so. Thick is better for maintaining viscosity in a multigrade oil, but, the thinnest oil appropriate for an application will yield the highest oil flow, and therefore the coolest temperatures....assuming the cooling fins/system is designed/functioning properly.

 

[sunruh]

hrk,
you have to understand that water does a better job as a coolant than either ethyelene glycol (EG) and propylene glycol (PG) do. don't take my word for it, take Dow's. they just happen to hold the patents for both. so if water cools better than EG and PG coolant/antifreeze does, do you really think oil would be close?
as titan mentioned, viscosity of the coolant plays a big part in the ability of the heat removal of a cooling system to transfer that heat away. the calorie (heat 1 gram of water 1 degree) is based solely on water. must be a reason for that.

mercury conducts heat better than water, but you can't pump it. there's that viscosity coming into the picture again.
so water, good. oil, not as good.

 

[hotroadking]

Thanks this is good the addition of information on coolants is good too.

I really wasn't trying to make a statement about oil and water other than we were having a discussion and the topic came up, not having a bunch of engineers on that site I came here as it's always been a good site.

Reading this, water can and does remove heat better than oil, and we have oil cooled motors, so coolant isn't an issue on HD's unless you have a Vrod.

It would seem then if oil isn't the best in cooling, it's good but not the best, adding an oil cooler to assist the oil in removing the heat would be beneficial.

 

[Titan]

Please don't take this as being too nit-picky, but, although an oil cooler would most certainly increase heat exchange (assuming it was correctly sized, the pump works fine, etc.), the ADDITION of one is only beneficial if the engine is overheating. IOW, if your engine runs optimally at about 212 degrees, and your oil cooler drops the temp to 200 or less, is this a benefit or not? However, if you are operating under conditions that are unusual, certainly there could be great benefit, even necessity, of having an appropriate added oil cooler. I'm really not trying to be picky, it's just that I see lots of people doing things to their bikes just because someone else did, and not because the overall function is improved.

 

[XS650]

quote:

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Originally posted by hotroadking:


Reading this, water can and does remove heat better than oil, and we have oil cooled motors, so coolant isn't an issue on HD's unless you have a Vrod.

It would seem then if oil isn't the best in cooling, it's good but not the best, adding an oil cooler to assist the oil in removing the heat would be beneficial.

---

To put some numbers to it ... The specific heat of water is 1.00 in English units. The specific heat of oil is about 0.45, meaning that oil has the ability to hold about 45% as much heat energy as the same amount of water for the same temperature change. So water will absorb over twice as much heat energy as oil for given temperature change.

Another way of looking at it is that oil has to be increased in temperature twice as many degrees to carry the same amount of heat out of your engine as water.

Antifreeze reeduces the ability of water to carry heat, so perhaps you should be comparing the oil to a 50/50 water/antifreeze mix which I recall has specific heat of about 0.8.

Titan gave you the most useful information though, get an oil temperature gauge first to find out where you are in temperature.

 

[Gary in Sandy Eggo]

Finally someone provided the answer to the question originally asked - specific heat comparison.

Not only does water have a higher specific heat, it also "wets" the surface it's absorbing heat from better than does oil. The higher viscosity oil forms a boundary layer at the metal interface (that's what makes oil a good lubricant). Heat has to travel THROUGH the boundary layer before it can be absorbed by the moving oil that would carry it away. The higher the viscosity, the thicker the boundary layer.

Regards, Gary in Sandy Eggo

 

[hotroadking]

XS and Gary, thanks that's what the question was inquiring about, does water provide a better source for removing heat.

As to oil coolers, if oil has half the capacity to hold heat as water, and you are in a non water environment such as an air cooled motor, then having a cooler provides a greater area for disbursing the existing heat in the oil regardless of the temp, the cooler will provider a way to quickly remove heat from the existing oil.

I don't see how the existance of an oil cooler is only beneficial if the motor is overheating. Seems to me the presumption is that if the motor isn't too hot then who cares. While that may be true to some extent, providing a cooler oil provides the ability to keep the engine running in a lower temp range, so when you get into those hotter running conditions, IE stop and go, the cooler will remove heat faster once you get moving, and the motor would be at a lower operating temp at all times.

Necessity isn't the issue, however the benefits are there, if you choose to use them is up to you.

 

[Titan]

Oil coolers are great, when oil temps are high. However, they need to function properly to keep the oil temp HIGH ENOUGH when not in high oil temp environments. Oil must get hot enough to provide ideal engine performance/economy/function if the engine, as well as burn off moisture/fuel within the engine system. The point is, too cool is, well, too cool! Oil cooler thermostats are essential for the best function, unless conditions are homogenous enough, and temps are monitored enough to give reliable operating range all the time.

 

[mechtech]

Water takes about twice as much heat as oil does [specific heat capacity] to raise any given volume one degree.

Water's thermal conductivity is about three times that of oil.

Water is used in cooling systems frequently, because of it's properties.

But like mentioned above, flow is important, and that's why there are water pumps on cars.

 

[carock]

You guys have different cooling capacity numbers than I am familiar with. I could be wrong, but oil's ability to remove heat is not just related to its specific heat capacity, but it is very related to it.Conventional dino oil is supposedly 69% effective as a cooing medium compared to water, and diester based oils 89% compared to water. I forget where I got these numbers from, it was at least 30 years ago. I have also forgotten just how these tests were performed, it was for a VW experiment. The experiment definitely showed that the diester based oils were the way to go for cooling.

 

[carock]

Amazing what a few hours can do for your memory. The oil vs. water cooling test I was referring to in the above post was performed to determine the best way to cool a VW Beetle cylinder head used in off road racing. The test was done in 1979. The VW cylinder head was extensively modified to accept water or oil cooling. The water or oil was passed through a radiator while the engine was running on a dyno. They varied the size of the radiator to get each coolant to run a 225F cylinder head temp with a 30 hp load. The dino oil (Valvoline 10-30W) required a radiator 50% larger than the water based coolant, the diester oil ( pretty sure it was Amsoil) required a radiator 24% larger. I remember that after hearing about this I also heard about Redline and I switched all air cooled cars over to Redline because they would run cooler, or so I theorized. I think the test showed that you could adequately cool an engine using oil instead of water.Some motorcycles do this today. Those motorcycles will run cooler using a diester based synthetic oil.