Glad I'm aircooled !

[Stig / Major Tom]

One pf the many reasons I like aircooled scooters (and cars, when I could buy them) is that I have no worries about the cold winters here in the Midwest, or back in NewEngland.
Nor do I have any worries about leaking fittings, failed pumps, holed radiators, cracked hoses, faulty thermostats, boiling over, etc., with an aircooled scooter.
Today's problem with the cold was finding the battery tender rubber ends so cold and stiff that it nearly prevented a connection!

It snowed twice today.
I was sorely tempted to fire up all the two-wheelers just to experience how they each started in the cold, and to hear them run.
I know some owners feel that is a good winter practice: start them, run them until they reach normal operating temps.
I never liked starting a very cold engine, if it not going to be ridden.
I rode daily when commuting through the Ohio winters - starting the scoot and giving it a little warm-up at 5:30am on many very cold days.
But,  it has been only a few days since each of these were ridden.
There are alot of 'old hand' theories about this - but I wonder if any lab has tested the practice of starting winter engines - versus not running them until the day they are ridden (driven)?
Stig

[CROSSBOLT]

Think about all the air cooled engines in Alaska!

Karl

[Mr. Paul]

I dont think there's any real harm in starting a cold engine as long as it is allowed to warm up some before being stressed.

[GLV55]

After reading about all the problems some liquid-cooled scooters experience (mainly the SYM HD200), I also have opted to never get anything but an air-cooled scooter. Yes, they may be smaller cc engines and all, but to me that's what a real scooter is - simple, easy to work on, and as uncomplicated as possible.

[Tromper]

Air-cooled vs. liquid cooled is a trade-off.
RE: GL's comments, the HD's foibles are overblown IMHO.  They seem to be model engineering, & QC issues vs. liquid vs. air.
In SYM's defense you do run into more engineering issues when using a newer design vs. a known and long since engineered through setup like the older air-cooled stuff.
The QC stuff is pretty inexcusable, but that's still not liquid vs. air-cooled.

I have had an air-cooled equivalent of the HD.

The S200 is technologically elegant in it's simplicity, easy to maintain, & essentially bullet-proof.

The HD did give me a fuel system issue they're known for, has more power, & gets better MPG.
For the coolant system.  Yup there is a layer of complexity there, only a couple hoses, & a radiator, but they do exist, & I have done mainteance on the coolant system on both the HDs I have kicking around.

For simplicity, I admire the S, & I'd probably have kept it if I had the space, but when space in the garage said one or the other I didn't really think hard on the matter.

[axy]

One pf the many reasons I like aircooled scooters (and cars, when I could buy them) is that I have no worries about the cold winters here in the Midwest, or back in NewEngland.
Nor do I have any worries about leaking fittings, failed pumps, holed radiators, cracked hoses, faulty thermostats, boiling over, etc., with an aircooled scooter.

Air vs. water cooled has little to do with riding in winter conditions.
As you can see from my signature, I have both at the moment, and had both in the past, including air-oil cooled 750 cc 4-cyl bike.
Air cooled bikes are much more simple. However, I have never had a problem with any of the items you mention with any of my bikes or cars (I am not saying other people do not have them, as it is a matter of statistics).
Water cooled scoot engines are typically 40 % more powerful than air cooled engines. This is something very, very important. Your average 125 cc 4st scoot if air cooled has up to 9 hp. If it is water cooled, it goes up to 15-16 hp. Something I cannot disregard.

Additional problem is regulations. For example, my GT300i is Euro 4 scoot. From 1st Jan 2018., in EU all scoots, even 50 cc, must have injection in order to pass emissions tests, and it is quite difficult if not impossible to achieve that with air cooled carb'ed engine.

While I do admire simplicity of Agility 125, I cannot ignore why water cooled may be better. Sheer difference in power output makes water cooled engine/scoot a better choice in most cases. Even when you compare for example Kymco's air cooled 2st (like in my ex. Cobra 50) with Piaggio's water cooled 50 cc 2st, water cooled has 60 % more power.

I would also be inclined towards saying that longevity of air cooled engines might be compromised in comparison with water cooled. This can be evidenced if you compare freshly changed oil of both scoots (I do that usually at the same time). In air cooled engines, oil becomes heavily poluted and black after a few weeks/few hundred kms. In water cooled engines, oil retains yellowish color even at change interval (few k kms/1 year).

[Stig / Major Tom]

Respectfully
Agreed - H2O =
  + HP - ✔
  + MPH - ✔
 
Longer engine life?? ..287,000 miles on my a/c VW (then traded for the new Rabbit)
My new a/c Piaggio meets the '18 Euro regs.

H2O = "meh"...for a % of us a/c riders/drivers.

Stig

[axy]

Respectfully
Agreed - H2O =
  + HP - ✔
  + MPH - ✔
 
Longer engine life?? ..287,000 miles on my a/c VW (then traded for the new Rabbit)
My new a/c Piaggio meets the '18 Euro regs.

H2O = "meh"...for a % of us a/c riders/drivers.

Stig

Well, this is why still everybody can choose a/c or w/c. In a small scoot, if you weigh 110 kgs like I do, 125 cc a/c 9hp does not even compare to 125 cc w/c 16 hp. It makes a world of difference. OTOH, if I lived in a third-world country (in full sense of that world), I would prefer technically less complicated scooter, and this is why in rural Africa and Asia, most scoots and even small bikes are a/c.

By a/c VW I guess you mean Beetle because almost all newer VW cars are w/c?

It is largely irrelevant because they are not only air cooled (like Kymco's scoots) but also oil cooled (different construction *and* they have a separate oil cooling radiator). Also, they were usually 1200-1500 cc 4-cyl air cooled engines developing measly 45-55 hp (<40 hp/l). Kymco's a/c 125 cc 1-cyl engine develops 9 hp (>70 hp/l), so it is already under much more stress. Comparison to a/c older cars is not exactly applicable.

[AMAC1680]

Yikes I’m old.
Time was “air cooled” and “vw” were one in the same !

AMAC

[axy]

Yikes I’m old.
Time was “air cooled” and “vw” were one in the same !

AMAC

... also when VW was pretty much making single car model. 😀

[de dee]

My first brand new car  1952 VW. convertible  25 HP.   RCAF Station Rockcliffe  408 sqad. parked on a hill to start the car when it was below -20 F.   

[hypophthalmus]

Since my engine blew, with the most likely culprit having something to do with the cooling system, I've come to view air cooling as an asset. One member here said that the small coolant passages trap air easily, even after bleeding, which is my best guess as to what happened. And it went from supposedly normal operating temperature to critically overheated very quickly.

Are oil cooled bikes more similar to air or water in terms of tight clearances and narrow operating temperatures? Somewhere in between?

With regards to water cooling increasing power -- not always? My water cooled People 250 produced I think 19hp. Air cooled cruisers (Yamaha, Suzuki) will produce more. Kymco's water cooled cruiser and Hyosung's oil cooled cruisers produce more than the air cooled, but not 40% more. For some reason, the sport bikes will be even more than that -- oil or water.

[axy]

Since my engine blew, with the most likely culprit having something to do with the cooling system, I've come to view air cooling as an asset. One member here said that the small coolant passages trap air easily, even after bleeding, which is my best guess as to what happened. And it went from supposedly normal operating temperature to critically overheated very quickly.

Are oil cooled bikes more similar to air or water in terms of tight clearances and narrow operating temperatures? Somewhere in between?

With regards to water cooling increasing power -- not always? My water cooled People 250 produced I think 19hp. Air cooled cruisers (Yamaha, Suzuki) will produce more. Kymco's water cooled cruiser and Hyosung's oil cooled cruisers produce more than the air cooled, but not 40% more. For some reason, the sport bikes will be even more than that -- oil or water.

Small 250 cc cruisers you mention usually have 2 cylinders, and not one, thus benefiting from synergy effect and therefore might be a bit more powerful than 1-cyl 250 cc engine.

Also, one should take into account whether the engine is 2 valves per cylinder or 4 valves per cylinder. Your typical 2-valve 300 cc engine in w/c scoots has 23-24 hp while the same engine with 4-valves has around 30 hp, only because of improved cylinder flow.

I guess, this thread is about scenario 2 valve per cylinder single cylinder that is air cooled or water cooled, and not other technical scenarios that might be possible in engineering sense of the word.

Finally, it seems that most people commenting do not fully understand the following cooling options:

- air cooled with fan (most "air cooled" Kymcos)
- air-oil cooled (with or without fan but with separate direct air oil cooler - VW Beetle and old 911s, Kawasaki sports touring bikes of 70s-90s)
- water cooled (without fan, usually small displacement w/c scoots)
- water cooled with fan (usually 300 cc scoots and bikes and higher)

They are all very different with different repercussions on the final engine power output.

Finally, a comment about two things from your post:

- "quick" passage from normal operating temperature to overheated: unfortunately, this is expected. Coolant temperature is usually 90-100 C. Boiling temperature of the new coolant is around 106 C. If something goes wrong, you will notice it in a matter of minutes in a car, or even sooner in a bike that has maybe 1,5l of coolant in the system.
- Clearances are much tighter in w/c engines because they are expected to work in a very narrow temperature range. A/C engines have looser clearances, the same with oil-air cooled engines. W/C engines have therefore higher compression ratio and proportionately higher power output. A/C engines have lower compressions and lower power output. Comparably and relatively speaking, w/c may be constructed to rev higher than a/c engines.

[hypophthalmus]

The advantage with the twins is that it's easier to get the smaller components to produce a higher rpm. In the case of the Yamaha twin, it's at 8000 instead of 6500 for the People 250.

There's the Suzuki GZ250, a single cylinder, two valve, air cooled engine that puts out about 1 hp more than the People 250.  Apparently still at 8000.

Even if you divide the HP by the number of revolutions, then it's about 20% less for the Suzuki single and 5% less for the Yamaha twin compared with the People 250.

Evidently the sports bikes have an even higher maximum engine speed as well -- mystery solved I guess.

[axy]

The advantage with the twins is that it's easier to get the smaller components to produce a higher rpm. In the case of the Yamaha twin, it's at 8000 instead of 6500 for the People 250.

There's the Suzuki GZ250, a single cylinder, two valve, air cooled engine that puts out about 1 hp more than the People 250.  Apparently still at 8000.

Even if you divide the HP by the number of revolutions, then it's about 20% less for the Suzuki single and 5% less for the Yamaha twin compared with the People 250.

Evidently the sports bikes have an even higher maximum engine speed as well -- mystery solved I guess.

Well, this whole story is not a single variable equation. Revs are also a function of bore x stroke, valve number, layout and size and overall ability to clear the cylinder of exhaust gasses. Last but not least, used materials because lighter parts tend to travel faster and generally, break sooner.