stop and go traffic

[qcbaker]

I just got finished riding back to work over my lunch break, and there was very heavy traffic due to an accident. I was in stop and go traffic for ~45 minutes, and luckily my bike did not encounter any problems during this time, but it got me thinking about problems this could cause in theory. So, I have a few questions I'd like to pose to the more knowledgeable members around here:

1. Since these bikes are air-cooled, would being in stop and go traffic for an extended period eventually cause an overheat? If so, how long would it normally take for this to be an issue?

1a. Since the air temperature outside is almost always going to be cooler than the engine, there is always some amount of cooling going on. Slightly more so for F models with the oil cooler, like my bike. Is this amount of temperature differential enough to keep the bike from overheating? If the bike is stopped entirely, it would eventually heat up the air surrounding the engine to a temperature at which it would no longer be effectively cooling, wouldn't it (assuming there is little/no wind)? With that in mind how much effect would wind or moving the bike side to side have? I guess wind effect would probably entirely depend on how strong the wind is, but the question remains.

2. How long can the battery be sustained by the charging system at low RPMs? I know from first-hand experience that the charging system alone is not enough to keep the battery from draining at least a little bit during idle. So, how long would you have to be in stop and go traffic for it to really start to cause an issue?

[lefty1615]

1. I may be pulling this out of my ass but I think on hotter days there is some risk of overheating, I know that mid summer in stop go my engine will read a good 20-30Deg Celcius higher than at highway speeds (according to my vapor gauge which reads off a crush washer sensor deal on the spark plug, hard to say how accurate it is.

1a. any air heated by the engine will rise and cooler air will replace it so you'll never have a situation where it isnt cooling but the engine is always producing heat as well. With that in mind you'll essentially reach an equilibrium point where the engine temp is constant because as the temperature difference increases, engine gets hotter, the rate of cooling will increase.
This is a basic physics principle where the rate of cooling, lets call it r, is determined by r = C(DeltaT) where C is some number representing the effective cooling rate between your material, in this case your engine and the air, and DeltaT is the difference between the material temp.

Whether or not that equilibrium point is below the overheating point for the engine will be dependant on how hot it is outside, because of that DeltaT term, and how efficiently the engine sheds heat.

2. Curious about this myself

[ShowBizWolf]

2. Curious about this myself

+1 !

[qcbaker]

1. I may be pulling this out of my ass but I think on hotter days there is some risk of overheating, I know that mid summer in stop go my engine will read a good 20-30Deg Celcius higher than at highway speeds (according to my vapor gauge which reads off a crush washer sensor deal on the spark plug, hard to say how accurate it is.

1a. any air heated by the engine will rise and cooler air will replace it so you'll never have a situation where it isnt cooling but the engine is always producing heat as well. With that in mind you'll essentially reach an equilibrium point where the engine temp is constant because as the temperature difference increases, engine gets hotter, the rate of cooling will increase.
This is a basic physics principle where the rate of cooling, lets call it r, is determined by r = C(DeltaT) where C is some number representing the effective cooling rate between your material, in this case your engine and the air, and DeltaT is the difference between the material temp.

Whether or not that equilibrium point is below the overheating point for the engine will be dependant on how hot it is outside, because of that DeltaT term, and how efficiently the engine sheds heat.

2. Curious about this myself

First of all, great post! Secondly, I guess what I really mean to ask then is: how long would it take to reach the point at which R=0 (if i understand your equation correctly), given no other factors (wind, moving the bike, etc.)? I guess that would depend on the outside temperature...  Maybe someone else on here has at least a good rule of thumb in lieu of actual numbers lol.

Also: What engine temperature is considered "overheating"? And is the engine temperature at R=0 greater than that temperature?

[The Buddha]

People have overheated the GS and even seized up. Now was it low on oil was it in stop and go was it due to some earlier problems - no idea.
Cool.
Buddha.

[Watcher]

I'm willing to bet your legs would be getting pretty damn hot as well if it was getting to the point of overheating enough to be damaged.
If you are starting to get uncomfortable, it's a good bet so is the bike.

You probably have increased risk with a faired GS opposed to a naked one, since there's no "static" airflow, but unless you are in 100°F heat I don't think the risk is that great.


Regarding the battery it doesn't take much to boost the charging system in terms of RPM.
Unless you are just letting the bike be pulled along at idle the small revs you'd give the bike every time you go should compensate for the drain when you stop.
I'd assume, at least...


I commuted by GS every day for almost a whole year, from stop and go to smooth, from rain and cold to the dead heat of summer.
Never drained a battery and never overheated.

[lefty1615]

First of all, great post! Secondly, I guess what I really mean to ask then is: how long would it take to reach the point at which R=0 (if i understand your equation correctly), given no other factors (wind, moving the bike, etc.)? I guess that would depend on the outside temperature...

Thanks! I was actually sitting through a (quite slow) heat transfer lecture so I got inspired to get a bit technical.

To answer the following up question, no R never equals zero, keep in mind that the outside temperature is constant so DeltaT is always positive for an engine and, we can assume, always greater than zero when the engine running. Similarly C is always a positive number so multiplying the two we will never get zero or less than zero.

So what's happening is that the combustion process produces heat which dissapates into the engine block, call this R1. Then the heat transfers from the engine block into the surrounding air in the cooling process, call this R2. So what happens at equilibrium is R1 = R2 and the overall temperature of the engine block will remain steady.

As to the overarching issue of overheating the bike personally I lean to the assumption that if your bike is properly maintained and your not in some crazy desert heat it won't overheat. I imagine Buddha's point of low oil or some such is likely the culprit. I would like to think the engineers at Suzuki at least considered the possibility that you might have to idle.

That being said if I know I'm at an extremely long light, like 2 minutes, I generally will just shut the bike off to save gas. If your in level ground and traffic is mad slow you can probably keep up just shuffling anyways right?

[qcbaker]

...
You probably have increased risk with a faired GS opposed to a naked one, since there's no "static" airflow, but unless you are in 100°F heat I don't think the risk is that great.
...

I wonder if the oil cooler was added to the F model specifically because of the decrease in airflow due to the fairings.

[qcbaker]

Thanks! I was actually sitting through a (quite slow) heat transfer lecture so I got inspired to get a bit technical.

To answer the following up question, no R never equals zero, keep in mind that the outside temperature is constant so DeltaT is always positive for an engine and, we can assume, always greater than zero when the engine running. Similarly C is always a positive number so multiplying the two we will never get zero or less than zero.

So what's happening is that the combustion process produces heat which dissapates into the engine block, call this R1. Then the heat transfers from the engine block into the surrounding air in the cooling process, call this R2. So what happens at equilibrium is R1 = R2 and the overall temperature of the engine block will remain steady.

As to the overarching issue of overheating the bike personally I lean to the assumption that if your bike is properly maintained and your not in some crazy desert heat it won't overheat. I imagine Buddha's point of low oil or some such is likely the culprit. I would like to think the engineers at Suzuki at least considered the possibility that you might have to idle.

That being said if I know I'm at an extremely long light, like 2 minutes, I generally will just shut the bike off to save gas. If your in level ground and traffic is mad slow you can probably keep up just shuffling anyways right?

Ahh okay, I get what you're saying. So then, would the amount of time it takes for the bike (at idle) to reach the point where R₁=R₂ be affected by the outside air temperature? I feel like it would have to... If its 20 degrees out, it would have to take much longer for the bike to reach that point than if it were 100 degrees out, right?

As for the actual issue of overheating, you and Watcher are probably right that the risk is minimal. And I just checked my oil today and the level is right where it should be, and the oil was put in there semi-recently, so theoretically I shouldn't have a problem with cooling under normal conditions. Like I said, I didn't actually have any overheating or battery problems, I just started to wonder about these things while I was in traffic.

[Suzuki Stevo]

Synthetic oil will still be oil at temps that dyno juice would fail at, couldn't hurt if your worried about stop and go? 

[lefty1615]

Ahh okay, I get what you're saying. So then, would the amount of time it takes for the bike (at idle) to reach the point where R1=R2 be affected by the outside air temperature? I feel like it would have to... If its 20 degrees out, it would have to take much longer for the bike to reach that point than if it were 100 degrees out, right?

Exactly, and the temp at which R1 = R2 will be higher. So if your bike just overheats at say 35deg celcius it likely won't ever overheat at 20deg celcius.

Synthetic oil will still be oil at temps that dyno juice would fail at, couldn't hurt if your worried about stop and go? 

I'd be curious to know of synthetic oil has better heat transfer properties or vice versa, I'm sure it could have a pretty big impact on the situation

[Suzuki Stevo]

I'd be curious to know of synthetic oil has better heat transfer properties or vice versa, I'm sure it could have a pretty big impact on the situation

For heat transfer I am assuming it would be worse, because it retains it's viscosity (stays thick)

Granted we are talking about an air cooled engine...but in the water cooled world, straight  Ethylene Glycol or even a 50/50 mix transfers heat far WORSE than just straight water.

Heat transfer in a stop & go situation would not be my concern, my oil retaining enough viscosity to keep metal to metal contact from happening would though 

[Watcher]

I'd be curious to know of synthetic oil has better heat transfer properties or vice versa, I'm sure it could have a pretty big impact on the situation

For heat transfer I am assuming it would be worse, because it retains it's viscosity (stays thick)

I think it would be BETTER.  Synthetic molecules are less likely to break down under high heat so it retains optimal fluidity.

[Suzuki Stevo]

I think it would be BETTER.  Synthetic molecules are less likely to break down under high heat so it retains optimal fluidity.

Yes it retains it's fluidity when cold...it also retains it's viscosity (stays thick) when hot.

[qcbaker]

...
Granted we are talking about an air cooled engine...but in the water cooled world, straight  Ethylene Glycol or even a 50/50 mix transfers heat far WORSE than just straight water.
...

Isn't that because ethylene glycol is added not to aid in cooling, but to prevent freezing? Correct me if I'm wrong here.

[Suzuki Stevo]

Isn't that because ethylene glycol is added not to aid in cooling, but to prevent freezing? Correct me if I'm wrong here.

Correct, but if you want to overheat anything water cooled use pure antifreeze, straight water (viscosity 0.890 cP) transfers heat in a cooling system better than (thicker) pure antifreeze. So on that premise in an air cooled engine if you used 90W gear oil instead of say 30W motor oil, the thicker more viscous gear oil would not transfer heat as good as the thinner less viscous motor oil. Yes I'm pulling all of this straight out of my ass but do you see the connection with heat transfer? Because that's what we where talking about.

[Watcher]

... air cooled engine if you used 90W gear oil instead of say 30W motor oil, the thicker more viscous gear oil would not transfer heat as good as the thinner less viscous motor oil.

Then why is it common practice to use a thicker oil in higher heat applications?
Even the chart in the GS500 manual reflects this, it shows temp ranges based on viscosities and the trend is thicker for higher temperature.


My Buell calls for 20W50 full synthetic, manual specification, and it's an air-cooled monster of a bike.  If thicker oil wasn't as good at heat transfer I'd think they wouldn't be recommending me one of the thickest viscosities of motor oil available.


I'm kind of spit-balling too, though.  I'm far from an expert in this stuff.
But I can see how since a thinner oil can circulate easier it is going to travel through the oil coolers and such faster.  At the same time it may not be able to pick up as much heat to bring to the cooler.
But that's less to do with the actual heat transfer rate and more to do with the circulation rate.
A thicker oil may have more capacity to absorb heat and once it's in the cooler it may be able to expel just as well as a thinner oil, especially considering if it's exposed to the cooler longer due to a slower overall flow rate.


Honestly in practice the difference might be marginal.
Like, imagine one small high velocity fan vs one large low velocity fan.  The low velocity fan may move just as much CFM as the small one, and can regulate a larger area, while the smaller one may handle a local area better but over time cannot maintain the temperature of the whole area.
So they have the same transfer rates, but which one handles heat better?
Relating to my computer, if I didn't have large fans circulating the air in the case the small fans on the chipsets would eventually succumb to a higher overall internal temperature.  They can pull heat away quickly but they can't expell it so efficiently.
At the same time if I took out the small fans on the chipsets the large fans in the case wouldn't be able to effectively keep certain chips cool enough...  So you run both, small fans on the chip and large fans on the case.
You can't run two weights of oil in an engine to handle separate jobs, so you compromise.  Thin enough oil to move quickly through the system, while thick enough to handle the heat.

[qcbaker]

Correct, but if you want to overheat anything water cooled use pure antifreeze, straight water (viscosity 0.890 cP) transfers heat in a cooling system better than (thicker) pure antifreeze. So on that premise in an air cooled engine if you used 90W gear oil instead of say 30W motor oil, the thicker more viscous gear oil would not transfer heat as good as the thinner less viscous motor oil. Yes I'm pulling all of this straight out of my ass but do you see the connection with heat transfer? Because that's what we where talking about.

I get what you're saying, but I'm not sure the viscosity of a liquid is directly linked to its heat transfer ability. Antifreeze just happens to be more viscous than water, I'm not sure that particular property of it has any real impact on its ability to transfer heat. As Watcher pointed out, it is common practice to use heavier grade oils in higher-heat applications.

I believe the property of any given material directly related to its efficiency as a cooling liquid would be specific heat capacity. If I'm wrong, lefty can probably correct me. He seems to know quite a bit about physics lol.

[Suzuki Stevo]

Yeah...that was my angle 

[lefty1615]

I get what you're saying, but I'm not sure the viscosity of a liquid is directly linked to its heat transfer ability. Antifreeze just happens to be more viscous than water, I'm not sure that particular property of it has any real impact on its ability to transfer heat. As Watcher pointed out, it is common practice to use heavier grade oils in higher-heat applications.


I believe the property of any given material directly related to its efficiency as a cooling liquid would be specific heat capacity. If I'm wrong, lefty can probably correct me. He seems to know quite a bit about physics lol.

Quick Disclosure, I had to look around a little before I wrote anything, too many terms floating around when you deal with academics haha.

Your basically on the ball here. Specific heat capacity isn't generally used to do these kinds of calculations as it is related to mass but they are related and I believe, one can be found or at least closely estimated with the other.