Had a discussion today with a friend who rides a CB500. He said that air cooled engines would seize if they were left at idle for a long time (several hours)
Is that true? Surely the engine would get extremely hot but would it actually break down and cause permanent damage?

It depends on the engine I think.  In general probably not.  It's hypothetical; why would you idle a motorcycle engine for hours? durr

"If you drink enough water you'll die!"

A water cooled won't necessarily do better, especially if there's no fan on the radiator.

But I'm no engineer, I'm just parroting what I've read...

I don't know how long it would take to seize, but you will destroy the oil if you let it sit and idle without any airflow over the engine. Twenty minutes or so sitting in one spot and the oil will start to break down and lose viscosity. When the viscosity gets low enough the oil has trouble maintaining a film between moving parts. Metal on metal moving parts gets very expensive rather quickly.

It doesnt follow one is better than the other. If the air cooled engine can radiate its heat at standstill nothing adverse would happen, same applies to the water cooled engine, it all depends on design factors. Given that water cooled engines rely on a fast airflow passing over a cooler/radiator and generaly lack cooling fins my money would be on the air-cooled engine lasting longer.

None of this realy matters though, both engines would suffer melted plugs, fuel vaporisation or pre-ignition and cut out way before serious any mechanical damage happened. 

I have heard all this "my bike is better than yours cos its liquid cooled" crap before. Go back to your pal and tell him you dont have a waterpump to sieze, or a seal to fail or a rad/hoses/seals/gaskets to burst and that you would be prepared to give him a lift home on the back of your old air-cooled GS5 if he had a cooling system failure miles from home and see what he says 

Some air cooled engines (specifically the new Triumph twins) have plastic oil pump drive gears that will melt if the oil temp rises too high.  I've seen it twice now where a customer started the bike on the enricher and then walked away and forgot about it.   Makes a real mess.  I've also seen Harleys make some real strange (read bad) noises after sitting in traffic for hours at Bike Week here in NH.

I suppose the lesson to be learned here is: Generally, bikes are made to run, not sit.

Even if some engines can't sit long, the GS tends to be pretty bombproof. In my years of being here I don't remember anyone talking about their bike having problems from overheating. A lot of people use them as commuters too, so they probably spend plenty of time sitting in traffic. I've spent time sitting in traffic not moving on the GS and a liquid cooled bike, and to be honest the liquid cooled bike was pumping out way more heat onto my legs, so the GS must not be too bad.

Your friend is also forgetting how much friendlier an air cooled bike is to work on. The next bike I'm planning on buying is (a newer)air cooled bike, and I'm actually considering that a positive considering I work on my bikes myself.

romulux covered my first thought:

why the f#ck would you let a bike sit at idle for hours?  wouldn't that be a catastrophic waste of fuel?

My second though is:

since an air cooled engine is an inherently simpler design, wouldn't there be fewer mechanisms to break down under stress, and could hypothetically be able to take more abuse before sh!t starts breaking down? 

I'm not an engineer, so my logic may be flawed, but there is beauty in simplicity.  The fewer steps there are in the process, the less likely there is to be a mistake.

As a city dweller, I can say that if I'm stopped in traffic, and it looks like I'm going no where fast, I'll just shut my bike off while I sit in traffic, especially if it's flat, or ideally downhill and I can just push/coast my bike as we move a foot every 10 minutes. As long as you don't restart it every 30 second for 20 minutes you don't kill the battery if you have to restart it once or twice.

As far as leaving a bike idling for hours, I can see how it'd happen. You start the bike, are half way through buckling your helmet, and all of a sudden "shaZam!, I forgot I had to write that history paper tonight!". I mean really, is it worth turning your bike off just for a couple hours while you're in your bedroom typing a 10 page paper? Hardly. 

Generally, an air coled engine will tolerate running at higher than 'normal' temperature better than a water cooled, because if the water temp goes above a certain point it boils off. In an air cooled, the higher the temp gets, the greater the rate of heat loss so the temp will eventually stabilise. Even with no wind, there will be some air flow around a stationary engine, as the hot air rises off the engine. Also, the amount of heat generated by the engine is related to the amount of fuel being burned, and you don't burn much at idle.
I'd be surprised if you couldn't idle a GS indefinately with no problem, as long as the ambient temperature is not ridiculously high. Not about to try it though!

I've heard that a GS will never reach normal operating temperatures when it's warming up at idle if it's under 60 degrees or so, which would make me assume that if it's 60 or below your bike will only cool down below operating temperature if you're sitting to long. That would make me assume that at normal temperatures your bike will only get hot, and not actually overheat.

That's just info I've read on this forum though, so if it's wrong, that's YOUR fault!

Has anyone ever installed a temp gauge on a GS5? It would be interesting to get scientific data. I've ridden in traffic at 100 degrees before and didn't worry about it.

Quote from: AccidentalF on May 10, 2010, 10:16:28 AM
I've seen it twice now where a customer started the bike on the enricher and then walked away and forgot about it.
I suppose the lesson to be learned here is: Generally, bikes are made to run, not sit.

HAHAHA who does that? lol

and you can tell your buddy, in addition to the water pump seizing, etc... what he said ^ all his cooling parts also add weight that your gs does not have. his radiator and hoses and coolant definatly weigh more than your cooling fins 

I run mine for hours to get the AC cool before I head off

Seriously, though I ride her in Fl on the I-4 parking lot and have never had a problem. Longest I sat in traffic was a couple of hours due to a shooting near I-4.

Mary

Quote from: XealotX on May 10, 2010, 08:10:10 PM
Has anyone ever installed a temp gauge on a GS5? It would be interesting to get scientific data. I've ridden in traffic at 100 degrees before and didn't worry about it.

I'm curious as well, but I'm more interested in knowing what temps are ok when they are measured from the spark plug sensor that comes with the Veypor gauges.  Freshly rebuilt engine, only started twice before relocating from AZ to OH and wondering what the temps mean!

http://gstwins.com/gsboard/index.php?topic=27008.msg284738#msg284738

There are tradeoffs with either, like any other engineering choice.

Having seen enough coolant leaks, pump problems and thermostat problems on a housemate's watercooled bike, not to mention another friend discovering why you really don't want a CX500 (certain era of one of the various different things Honda has called a silverwing - one prone to water pump drive shearing off) I'm generally happy with air cooling as part of the keep it simple, stupid philosophy of things that might actually work and keep working.

I know it's superficial, but air cooled bikes look better too. If you're counting pros and cons it could be tossed in there.

It doesn't matter whether the engine is water cooled or air cooled; it will seize if left idling too long.

Generally, water cooled engines have a fan and radiator, which helps reject some heat when the bike is left to idle. So, the bike can sit longer than would be safe on an air cooled engine. However, very few motorcycles have a fan and radiator large enough to keep the temperature in check without sufficient airflow over the engine. The Ninja 250 I used to ride had a small radiator, and would overheat very quickly. The GSXR 600 I owned would also overheat if allowed to sit for 15 minutes or so.

I do have one bike that could idle almost indefinitely; a BMW K1300GT. But, the size of the radiator and fan must be seen to be believed.

If I understand it correctly, the primary advantage of water cooling is that it keeps the temperature of the engine somewhat consistent. Consistent temperature means that the metals in the engine don't expand or contract as much relative to each other as they would in a air cooled engine. The reduction in thermal expansion issues means you can run tighter tolerances, which means you can spin the engine up higher, and produce more horsepower.

Heat dissipation increases with temperature.  It would be interesting to know if the GS engine is designed so that it will reach a temperature where it dissipates as much heat as it produces so the temperature reaches a steady level.

I told my friend about a few of the disadvantages with water cooling, and he agreed with some of it. He still believes that water cooling is better though.

If water cooling was always better, all bikes would be water cooled.

As always, there are advantages and disadvantages to each technology. Understanding the differences is valuable. Attempting to argue about which is better really isn't.

I've owned a reasonable collection of air and water cooled bikes. Air cooling works very well on twins. IMO, it's not ideal for 4 cylinder engines.