stop and go traffic

[mr72]

... 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.

Oil's job is not cooling, it's lubrication. At lower temperatures it flows less easily making it harder on the oil pump and also less likely for it to find its way into small spaces where it needs to be in order to lubricate properly... mostly at cold startup. Once the engine is hot, the higher viscosity oil is better as long as it is thin enough when it is a film to fit between things that must be lubricated, like the rings-cylinder, cam journals, rod bearing, etc.

And BTW 90W gear oil is the equivalent of 40W SAE motor oil. Gear oil viscosity is on a different scale than motor oil.

Now, regarding how well water cools engines vs. ethylene glycol, it's mostly about the thermal resistance, or the reciprocal function thermal conductivity. Here's a handy chart:
http://www.engineeringtoolbox.com/thermal-conductivity-liquids-d_1260.html

Notice water is over 2x as conductive as ethylene glycol. There are other factors as well, such as how much surface area of the engine's cooling surfaces is in contact with the coolant. This is where the viscosity of water gives it a slight additional edge, since it flows into smaller spaces more rapidly than anti-freeze but this is a marginal difference. If you really want to improve cooling then you can add a surfactant such as Redline Water Wetter to distilled water in the coolant that will break the surface tension of the water and allow it to "coat" the cooling surfaces better... water's surface tension will ordinarily cause it to sort of "float" on top of irregular surfaces, for example it won't just flow all the way into micro grooves in a machined surface etc., but WW will allow it to flow more readily and increase surface area by some margin so you get better heat transfer into the coolant and also better heat transfer from the coolant to the radiator. It's all on the margins but if you have an engine that either has a high penalty for overheating (like my Miata's engine) or that has a marginal cooling system (water-cooled VWs) then every bit matters.

BTW, ethylene glycol not only lowers the freezing temperature of engine coolant compared to straight water but it also increases the boiling temperature, so it's a catch-22. Once the water boils in a H2O engine, it will no longer cool successfully and you are going to overheat in no time. Straight water may cool better in ordinary use, but it is more likely to boil, which is bad. Water Wetter increases the boiling point very slightly. There are also other chemical concerns with different formulations of anti-freeze (OAT, HOAT, P-HOAT, etc.) wherein some are more or less compatible with certain cooling system hard parts and some are not compatible with others so you can't mix and match. There's a bit of an art to water-cooled engine cooling... drive a high-revving sports car in rush hour traffic in Austin TX for a couple of decades and you'll be forced to figure it out like I was.

It's all irrelevant for an air-cooled engine. The king of air cooling is surface area of the heat sink, in this case the entire surface of the engine that is exposed to the air, including the crankcase and covers and sprocket and chain and everything else, to an extent, that is mechanically coupled to the engine. A lot of the friction in the engine is in the piston-to-cylinder interface, and the heat from combustion is present directly in the cylinder, which is why it makes the most sense to form the cylinder into a giant heat sink, making it out of aluminum with fins cast into it so you maximize surface area sufficient to cool the engine in most cases. It's the heat transfer between the cylinder fins and the air around it that cools the engine, and aluminum-to-air has a better thermal conductivity than steel (or iron) to air, which is why most air cooled motorcycle cylinders are made of aluminum alloy. There's a huge tradeoff in durability, emissions, fuel economy, oil consumption, etc., but it's worth it for the cooling improvement.

The difference in temperature between the air and the cylinder fins basically defines the rate at which you can cool the engine, so sitting in traffic in hot weather is bad since the air directly in contact with the cylinder fins becomes hot quickly and is not displaced by new cool(er) air as quickly as it is when you are moving. If you really want to avoid overheating in stop and start traffic it's simple. Reduce the cause of heat to begin with by using the best engine oil you can to reduce friction, keep the level high enough so you don't starve the piston rings for oil, don't let the idle mixture be lean since lean running is higher combustion temperature, and keep the idle speed low as possible. Don't "blip" the throttle while sitting like all the kids like to do with their 4-cylinder water-cooled motorcycles.

A small fan of some kind wouldn't hurt even for an air-cooled engine. VW and Porsche used a big crankshaft-driven fan to ensure air is always moving if the engine is running. But it'd look funny on a GS500.

[qcbaker]

Oil's job is not cooling, it's lubrication. At lower temperatures it flows less easily making it harder on the oil pump and also less likely for it to find its way into small spaces where it needs to be in order to lubricate properly... mostly at cold startup. Once the engine is hot, the higher viscosity oil is better as long as it is thin enough when it is a film to fit between things that must be lubricated, like the rings-cylinder, cam journals, rod bearing, etc.

And BTW 90W gear oil is the equivalent of 40W SAE motor oil. Gear oil viscosity is on a different scale than motor oil.

While that is true, oil in air cooled motorcycles (especially ones with oil coolers, like the GS500F) does play a part in removing heat from the engine as it circulates.

Now, regarding how well water cools engines vs. ethylene glycol, it's mostly about the thermal resistance, or the reciprocal function thermal conductivity. Here's a handy chart:
http://www.engineeringtoolbox.com/thermal-conductivity-liquids-d_1260.html

Notice water is over 2x as conductive as ethylene glycol. There are other factors as well, such as how much surface area of the engine's cooling surfaces is in contact with the coolant. This is where the viscosity of water gives it a slight additional edge, since it flows into smaller spaces more rapidly than anti-freeze but this is a marginal difference. If you really want to improve cooling then you can add a surfactant such as Redline Water Wetter to distilled water in the coolant that will break the surface tension of the water and allow it to "coat" the cooling surfaces better... water's surface tension will ordinarily cause it to sort of "float" on top of irregular surfaces, for example it won't just flow all the way into micro grooves in a machined surface etc., but WW will allow it to flow more readily and increase surface area by some margin so you get better heat transfer into the coolant and also better heat transfer from the coolant to the radiator. It's all on the margins but if you have an engine that either has a high penalty for overheating (like my Miata's engine) or that has a marginal cooling system (water-cooled VWs) then every bit matters.

BTW, ethylene glycol not only lowers the freezing temperature of engine coolant compared to straight water but it also increases the boiling temperature, so it's a catch-22. Once the water boils in a H2O engine, it will no longer cool successfully and you are going to overheat in no time. Straight water may cool better in ordinary use, but it is more likely to boil, which is bad. Water Wetter increases the boiling point very slightly. There are also other chemical concerns with different formulations of anti-freeze (OAT, HOAT, P-HOAT, etc.) wherein some are more or less compatible with certain cooling system hard parts and some are not compatible with others so you can't mix and match. There's a bit of an art to water-cooled engine cooling... drive a high-revving sports car in rush hour traffic in Austin TX for a couple of decades and you'll be forced to figure it out like I was.

It's all irrelevant for an air-cooled engine. The king of air cooling is surface area of the heat sink, in this case the entire surface of the engine that is exposed to the air, including the crankcase and covers and sprocket and chain and everything else, to an extent, that is mechanically coupled to the engine. A lot of the friction in the engine is in the piston-to-cylinder interface, and the heat from combustion is present directly in the cylinder, which is why it makes the most sense to form the cylinder into a giant heat sink, making it out of aluminum with fins cast into it so you maximize surface area sufficient to cool the engine in most cases. It's the heat transfer between the cylinder fins and the air around it that cools the engine, and aluminum-to-air has a better thermal conductivity than steel (or iron) to air, which is why most air cooled motorcycle cylinders are made of aluminum alloy. There's a huge tradeoff in durability, emissions, fuel economy, oil consumption, etc., but it's worth it for the cooling improvement.

The difference in temperature between the air and the cylinder fins basically defines the rate at which you can cool the engine, so sitting in traffic in hot weather is bad since the air directly in contact with the cylinder fins becomes hot quickly and is not displaced by new cool(er) air as quickly as it is when you are moving. If you really want to avoid overheating in stop and start traffic it's simple. Reduce the cause of heat to begin with by using the best engine oil you can to reduce friction, keep the level high enough so you don't starve the piston rings for oil, don't let the idle mixture be lean since lean running is higher combustion temperature, and keep the idle speed low as possible. Don't "blip" the throttle while sitting like all the kids like to do with their 4-cylinder water-cooled motorcycles.

A small fan of some kind wouldn't hurt even for an air-cooled engine. VW and Porsche used a big crankshaft-driven fan to ensure air is always moving if the engine is running. But it'd look funny on a GS500.

Now THIS is podracing... Great info!

[Suzuki Stevo]

As said above...good oil at the right level and don't blip the throttle, as a rider that's really all you can do in stop and go traffic to keep the heat down.

[gsJack]

My opinion of the importance of oil viscosity to the cooling of air cooled engines copied from old post of mine:

Use 10w-40 or 15w-40 unless you have a high oil consumption problem and really need the 20w-50.  I put 15W-50 Mobil 1 synthetic in my 97 GS for about 45k miles after breaking it in on 10W-40 dino for 5k miles and when oil consumption increased I switched to the cheaper 15W-40 Rotella T for the next 30k miles.  I used the 15W-40 Rotella T in my 02 GS for all it's 100k miles.  Engine wear due to miles seems to have progressed about the same on both bikes regardless of oil type.

My 97 GS progressed from regular to mid grade to premium gasoline to prevent gas knock in hot weather as the miles and carbon built up same as the 4 Hondas I used 20W-50 in summers did previous to the GSs.

When I switched from the 15W-50 to the 15W-40 in the 97 I went back to regular gas year round without gas knock and have used regular gas all my 100k miles on the 02 also w/o knock.

The GSs run cooler on a xxW-40 oil than on a xxW-50 oil and your doing it no favor using the heavier oil in hot weather unless oil consumption is real bad.  Besides lubricating the engine the oil also provides cooling by carrying heat away from the head to the sump.  This cooling flow is reduced with the heavier oils.

[Watcher]

@mr72 

In the case of an oil cooler you can say oil plays a larger role in temperature management.  But I agree that the actual fins provide a larger role in maintaining operating temp.

Food for thought, my Buell is air cooled but has several devices to aid it.

Oil cooler.  It's actually pointed indirect to air flow but with a scoop, presumably to avoid damage from rocks and such.
Either side has a scoop that directs air at the rear cylinder.
Under the seat and pointing straight at the rear cylinder head is an electric fan.





The rear cylinder needs all the help it can get, since it's half stuffed between a frame.

[mr72]

No kidding about the electric fan on the rear cylinder in a V like that.

I would think you could whip up a fan in some of the area taken up by the factory air box if you switched a GS to pods or lunchbox, possibly a fan and a duct to get the air where you want it. I don't think it's necessary but it wouldn't hurt especially if it were controlled by a temperature switch like in a car, so it would only come on for example when you are stopped in traffic and the temp rises a certain amount. I'd think switching it based on oil temperature would be a good idea, or just use some kind of thermal sensor affixed to the cylinder somehow.

[Watcher]

... it wouldn't hurt especially if it were controlled by a temperature switch like in a car, so it would only come on for example when you are stopped in traffic and the temp rises a certain amount. I'd think switching it based on oil temperature would be a good idea, or just use some kind of thermal sensor affixed to the cylinder somehow.

That's more or less how this one works.
It's noisy since it's a relatively high velocity fan, so I can hear when it switches on.  Usually comes on in traffic and may actually turn off at a steady 50mph or so, depending on air temp.  I can't hear it at those speeds and engine RPMs but sometimes after a stretch I'll come to a stop and I won't hear it.
It also stays on for a minute or two after the ignition is switched off.

Sort of a double edged sword, though.  It's designed to draw air away from the cylinder and ends up dumping it under the seat.
In the winter it means you don't completely freeze your nuts off.  In the summer...  Well, you can imagine.

[qcbaker]

That's more or less how this one works.
It's noisy since it's a relatively high velocity fan, so I can hear when it switches on.  Usually comes on in traffic and may actually turn off at a steady 50mph or so, depending on air temp.  I can't hear it at those speeds and engine RPMs but sometimes after a stretch I'll come to a stop and I won't hear it.
It also stays on for a minute or two after the ignition is switched off.

Sort of a double edged sword, though.  It's designed to draw air away from the cylinder and ends up dumping it under the seat.
In the winter it means you don't completely freeze your nuts off.  In the summer...  Well, you can imagine.

You're in AZ currently, right? I'd imagine having your bike dump a lot of heat onto your legs all the time in the desert heat could get pretty swampy pretty quickly. Is it a big problem for you?

[Watcher]

It's so dry here that you tend to avoid the "swamp" you would assume it causes.
That being said, the rear header wrapped around the right side causes more of a problem than the fan under the seat.
Even with that little heat shield it cooks the inside of your leg if you're at relatively low speeds.  I would have to push my knee out to catch some wind every now and then.

And the fan under the seat honestly isn't so bad.  Especially with the Corbin seat.  It has a further back seating area so you aren't so close to the spot in the subframe where it dumps out (right at your crotch).  It's also a much more rigid (thicker) basepan and a denser packing which would lead me to assume it takes longer for the heat to actually make it all the way through to my delicate region.

Also, you can see the spot in the subframe where the hot air exits.  It's by the rear brake fluid reservoir on the right side, and it's next to where my straps are hanging on the left.  So it's not like the air just stagnates under the seat, it does flow out.

I suppose I could always add some heat resistant material under the seat if it gets too uncomfortable.  I got the Corbin towards the beginning of autumn so I didn't have much time in the 100s to really give it a good test.

[philward]

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.

Don't forget about convection.  Even though your bike is stationary the air around the cylinder head is not - hot air rises!

[Atesz792]

That's more or less how this one works.
It's noisy since it's a relatively high velocity fan, so I can hear when it switches on.  Usually comes on in traffic and may actually turn off at a steady 50mph or so, depending on air temp.  I can't hear it at those speeds and engine RPMs but sometimes after a stretch I'll come to a stop and I won't hear it.
It also stays on for a minute or two after the ignition is switched off.

Sort of a double edged sword, though.  It's designed to draw air away from the cylinder and ends up dumping it under the seat.
In the winter it means you don't completely freeze your nuts off.  In the summer...  Well, you can imagine.

I assume it would not be too hard to buy a small fan designed for this (off a small car) at the wrecker, and install it either with a manual switch, or a temperature controlled one. I think one could even place it in front of the cylinders, it would not matter much at speed, but would be helpful once stopped when it's hot-hot-hot.

[mr72]

I assume it would not be too hard to buy a small fan designed for this (off a small car) at the wrecker, and install it either with a manual switch, or a temperature controlled one. I think one could even place it in front of the cylinders, it would not matter much at speed, but would be helpful once stopped when it's hot-hot-hot.

You can buy universal cooling fans for cars inexpensively, but most are going to be too big to fit in any of the spaces in a GS.

Plus, there is the problem is air pressure. Normally to make the fan work you would have to have essentially a shroud of some sort over the cylinders so that the fan will force air to be drawn across the fins rather than just picking up ambient air. This is not trivial to do, and would likely affect cooling to the degree that it would be necessary to run the fan all the time, and use a pretty big fan. The only reasonable place to put it is where the air intake is on the GS in place of the airbox, but then you have to find a way to get air in from somewhere besides the low-pressure zone created by the fan. There's just not much room to work with there. The engine was never really designed for this. If you make a "pusher" fan without any (or much) shrouding then you waste a lot of energy running the fan since the air is not being directed only over the fins so it would be terribly inefficient. And noisy, and bulky, and you are still stuck with the problem of where to put it.

I think on a GS500F there might be a really creative way to get forced air onto the head without first pulling it over the headers, but you'd have to fab up something quite ugly and bulk to put a "pusher" fan at the front of the bike pushing air over the head towards the rear. A duct and an air intake shroud up to the sides of the head tube/fork interface. Or just get a little bit of help from a small but powerful computer power-supply style fan mounted where the oil cooler mounts in front of the head and hope for the best. You might get a small amount of improvement... better than nothing I suppose. It would not be too weatherproof.

Anyway, in theory anything could be done but I doubt it's worth it. Of course I haven't ridden a GS500 in the TX summer yet, so maybe I'll be convinced it's a worthwhile effort by the end of August.

[Watcher]

There's also the fact that an open air fan, mounted up front, will turn from the air pressure from simply moving.
Fans that work backwards are generators, and this isn't particularly good for the fan or anything else connected to it.

Fans behind radiators are fine because there's not enough air pressure diffused through the radiator to turn the fan.
It's fine on my Buell because where it's tucked away there's almost no air flow without running the fan.
There's a reason you don't see them just hanging out up front suspended from the frame.

[mr72]

Yeah you'd ideally have it on a clutch so the blades could turn without turning the motor. Also you'd ideally have it draw air from a directed source so it isn't in the wind, but any air pressure difference will make it turn.

So nevermind, I can't imagine a good way to put a fan on a GS500. And the truth is, being simple and air-cooled is a big part of the charm.

In fact if I buy another bike, it'll most likely be a fully air-cooled twin like a Ducati Scrambler for this very reason. Fewer things is fewer things to go wrong.