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to air cool or not to air cool.

Discussion in 'Technical and Troubleshooting Torque' started by timbo79, May 20, 2009.

  1. Hey guys

    are there any significant down sides to having an air cooled engine compared to having a liquid cooled engine in say a gsf bandit 1200 compared to a 1250 bandit. do they suffer problems o ot days and is being air cooled an effective cooling system???

    thanx all

  2. Nothing wrong with air cooled bikes.
    80% of the reason bikes are water cooled is marketing
    19% is noise reduction
    1% is for sustained performance under race conditions.
  3. Air cooling has an impact on noise?
  4. Air/oil cooled engines idle higher when warmer than water cooled engines.
    Higher idle means noisier.
  5. Not only that the water jacketing disperses a fair bit of engine noise and top end clearances are tighter on a water cooled bike.

    Being a bit (only a bit) tounge in cheek with my first post.

    From a practicle standpoint owning an air cooled bike will mean little difference. You may need to change the oil a bit more often.

    With the GSXR1100 I used to get a bit nervous if I got stuck in the m5 tunnel on a hot day, but I never had an incident.

    The Bandit engine is the same just in a lower state of tune. So you wouldn't have any problems with that.

    Besides water cooling on bikes is not very good as it doesn't have the total volume or the radiator volume per given kW that a car does.

    Then consider that most modern air cooled bikes are in fact air/oil and the real differences become negligible.
  6. I've sat on a freeway jam in 38+ degree days on the bike and it has never missed a beat, apart from some pinging when under load but as soon as it gets moving that subsides very quickly.
    I'd hate to sit in peak hour with a water cooled engine and have the thermo fans cut in, the heat blast would be horrible in those conditions.
  7. My experience with my R11 was very similar. My K100, however, when the fan cut in (which wasn't that frequent really), would cook your buttocks and thighs medium rare where the air came out.

    My current DR650, on hot days, roasts the rider's right leg with heat from the high level exhaust and the backwash from the oil cooler but the rest remains comfortable. Meanwhile, the engine show no signs of distress.

    In bike quantities, good oil costs so little and is so easy to change that there is really no excuse for not changing it frequently.
  8. And you'll never have to change your coolant.
  9. I rode a water cooled bike (VTR250) on a hot day (36 degrees and mid afternoon) and got stuck in traffic. It was fine. I wasn't and got knocked around by the heat.

    I was apprehensive about getting my current bike for many reasons, including it being oil cooled. I rode it on a hot day (38 degrees) and was stuck/slowed by traffic a little. It was fine. I was too. I wisened up from last time.

    My conclusion is that it doesn't matter for lower performance engines whichever way it is cooled if you're using them normally (i.e. not constantly on the throttle stop). The service intervals are more frequent on my current bike (every 4,000 km).
  10. thanx everybody useful info makes my decision a little easier.
  11. No difference really, except generally aircooled bikes are naked or semi naked. water cooled are faired.
  12. From an end-user perspective, as everyone else posts, there is no difference - All the differences have already been considered by the engineers.

    Air-cooled engines run hotter, no doubt about that. It would take a fair bit of stationary idling to melt the top end of an air-cooled bike.
    Any engine builders here want to weigh in on hot spots within air-cooled and non-waterjacketed heads?

    As for the case of water cooled systems, even a "lightly" watercooled block would benefit with regards to deat dissipation - For Steel (closest I could find to Grey Cast Iron with regards to the 2-odd% Carbon Content), Density ≈ 7830 kg/m^3, Secific Heat ≈ 0.5 kj/kg*K, whereas for Water at 75oC, Density = 975 kg/m^3 and Specific Heat - 4.19 kj/kg*K
    (Çengel et al, 2006)

    Despite the lack of density relative to Grey Iron, it is easy to see how water is an appealing feature, especially with relation to quick heating of the cylinder and better temperature regulation - Less need for loose tolerances due to less predictable heat expansion.
  13. Your a bit off track with your analysis here mate. What maters in both cases is the area exposed to air and the air flow over it. In the case of the water cooled you are looking at the radiator design. Once up to temperature the water is only a means to transfer the heat to the radiator. The exposed engine would also add a little.

    In the case of air cooled you are looking at the area of the fins perpendicular to the air flow.
  14. there wont be problems now will there
  15. In the real world,

    Water-cooled engines in are almost always in a higher state of tune than air-cooled.

    Broadly speaking,the higher the state of tune the higher the temperature of the engine, the more effective and reliably you can cool the engine the higher the state of tune without cooking it or the oil.

    The noise difference as previously noted is because of water jackets around the engine, it has nothing to do with idle speed.

    It is also worth noting modern "air-cooled" engines also depend heavily on oil cooling and are almost as much oil as air cooled.

    As for it being a marketing con......Water-cooling is more expensive than Air, you only need to look at any "cheap" bike (hyosungs, chinese bikes etc) to see that.

  16. So an oil cooled Ducati and oil head beemer is cheap?
  17. OTOH, water cooled engines can be made of cheaper materials because areas like eg the exhaust ports and valves are kept cooler and so get an easier time of it.

    Considering some of the rubbish that the Japanese have made motorcycles out of over the years, I suspect that this may be a significant consideration.
  18. Nope, but they are making them because their customers want them, not for economic or technically (better) reasons. To my knowledge neither of those engines perform better than their water cooled contemporaries. The 1098r and s1000rr sure aren't air cooled.

    Much like Porsche keep making 911s with their engines out behind the rear wheels, it's what their customers want, not what is best for the purpose of the car, the fact they are still great is quite an engineering feat. They also had a hard time moving from air cooling due to customer demand.

    Some materials may be cheaper, but I'd imagine manufacturers would much rather do away with the extra weight and complexity of water cooling if their sole concern was saving money. The lowest/cheapest bikes of Japanese manufacturers are air cooled, cbf250, gs500, scorpio etc.

    To see the recent benefits of moving over to water-cooling look at the off road bikes, they traditionally stayed away from water for reasons of reliability (pierced radiators, loss of fluid etc) and weight, all the better (and higher output) single cylinder motards and off road bikes are water cooled these days, Leaving dinosaurs like the XRs and (some) DRs (bring on the water cooled, injected dr650!) behind.

    I'm not saying Air cooled engines suck, they certainly have their place, but generally speaking water cooled is better.
  19. The point, as I see it, is a water jacket is able to circulate closer and therefore transfer excess heat away quicker from the combustion chamber then the mass of an air cooled cylinder, due to less mass required between the chamber and the transfer medium (due to design considerations.)

    In relation to a radiator, at the same velocity you are looking at a significantly increased surface area of heat transfer, not including secondary heat transfer over the engine surfaces.
    I'd maintain that a small radiator has a significantly better surface area exposure then a large cylinder block, simply due to a "ribbon" construction and prominent/efficient location as opposed to a block behind a set of headers. Even due to prependicular construction, if you visualise the flow of air between the small gaps, you can entertain a certain amount of radiant transfer to the air.

    Keep in mind that hotter conditions are handled significantly better then an air-cooled engine - a fan on an air cooled engine is therefore significantly less efficient then a fan directly behind a radiator assembly, due to the respective flow over the surface areas
  20. Perhaps in terms of outright power, but in terms of torque and ease of maintenance I'd definitely like to be riding a Beemer or Duke instead of a Jap bike. Hell, 100 horses from an air/oil cooled litre(ish) twin isn't that bad, you gotta admit.

    Lets end this now.

    Air/oil cooled is great, fine, no worries. Everyday use will see no problems at all, neither will spirited riding. Sustained track use might see some problems, however. Essentially, you're looking at a bike that is adequately cooled for 95% of situations, the other 5% not being needed for the VAST majority of consumers. Performance is down on watercooled as mentioned, due to tolerance issues.

    Watercooled engines are also usable in everyday situations and spirited riding. Sustained track use is possible, but may still see some problems in engines not given enough care. Performance is up on air/oil cooled bikes due to tolerances and heat dissipation being improved. Differences in weight are negated by the power advantage. Maintenance is marginally more difficult and less frequent.

    I wouldn't sweat the decision. An good scenario to demonstrate is my father riding his Beemer R series down to Phillip Island and back with more than a few others. There was a mix of air and water cooled bikes, and the pace was fairly quick from what I've heard. No-one dropped back significantly, and if they did then I bet you it wasn't because of their bike being inadequately cooled.

    So, what're you buying a bike for? If its everyday situations and good fun then either will suffice. If you want the rush of 200 horses under you then get a Kwaka Z10. Otherwise, do whatever you want. Its how it feels to you that counts.

    Cheers - boingk