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-   -   This may be a stupid question - air cooled engines? (http://www.horizonsunlimited.com/hubb/other-bikes-tech/may-stupid-question-air-cooled-42944)

Michael_London 22 May 2009 22:46

This may be a stupid question - air cooled engines?
 
As i said above this may be a totally stupid question, but with an air cooled engine -

if you sit stationary for long periods of time with the engine running then the engine will gradually just get hotter and hotter as no air is passing by the engine - is this correct?

Will you get more heat given off, as in will you feel more heat coming from the engine as you sit on bike with an air cooled engine vs water cooled?

Thanks for any responses

Warthog 22 May 2009 22:53

Air-cooled engine loose heat through the cooling fins.

Yes, they do loose heat better with air passing over them, but I have sat in traffic for what feels like an eternity on several air-cooled bikes and have never had an engine failure, although I could feel the ambient temperature around the engine rising.

You'd have to leave it running for a good while to have problems, IMO.

On a water cooled bike the heat emitted from the einge is abosrb by the coolant. Once the temp reaches a set amount the thermostat will activate the fan to keep the bike from over heating...

On any bike, if it looked like I was going to sit there for a while, I just flicked the kill switch: no point in burning juice to go nowhere...

Michael_London 22 May 2009 23:03

Thanks for response tho if in future you could make it a bit quicker please! Lol

yes i would switch engine off, just was not sure if i was thinking along the right lines

palace15 22 May 2009 23:08

It is suprising how much heat is generated whilst the bike is 'at idle' whilst stationary, I noticed this one night whilst I was about to leave work in the dark, it was a 1340 Harley and after starting it I realised I had forgotten something and unlocked the shop and went back in for just a couple of minutes, upon returning to the bike, the exhaust pipes were glowing red hot on about 6-8inches out of the cylinder heads,this I had never seen before and never experienced this at either high speeds or over long distances, quite shocked at how the heat had built up in such a short space of time.

petefromberkeley 22 May 2009 23:22

Quote:

Originally Posted by Warthog (Post 242967)
Air-cooled engine loose heat through the cooling fins.

Yes, they do loose heat better with air passing over them, but I have sat in traffic for what feels like an eternity on several air-cooled bikes and have never had an engine failure, although I could feel the ambient temperature around the engine rising.

You'd have to leave it running for a good while to have problems, IMO.

On a water cooled bike the heat emitted from the einge is abosrb by the coolant. Once the temp reaches a set amount the thermostat will activate the fan to keep the bike from over heating...

On any bike, if it looked like I was going to sit there for a while, I just flicked the kill switch: no point in burning juice to go nowhere...


SHHHHHUSH! The way motorcycles got the right to split lanes (filter) in California was by claiming our air cooled engines would overheat.

Steve Pickford 6 Jun 2009 09:19

I always turn my engine off if it looks like I'll be waiting for more than a minute or two. I think that in Switzerland it's compulsory to turn off when waiting at traffic lights?

Another point to note: I've heard of some BMW oilheads catching fire or seizing when left idling for long periods. The engine overheats, the oil sight glass drops out & the hot oil spills on to the header pipes. This may have happened to Police bikes (R1150RT?) left idling in emergency situations with their lights on etc.

oldbmw 5 Aug 2009 22:30

BMW reccommend that the engine not be run stationary for a long time, I forget the figures, having sold my r80 no longer have the book. but it was either 2 minutes or ten.
as an aside, french BMW r1150's have a thermostat on the oil with a fan cooled oil cooler.

but yes, air cooled bike heat up when stopped.. My Enfield (lean burn) is the hottest bike I have ever come across.

TonyTea 6 Sep 2009 00:46

Most air cooled engines have fins which are set at an angle - not completely horizontal. That's because back in the days when air cooling was normal the designers knew the bikes would be stationary sometimes, and so the fins allow convection circulation. (warm air goes up past the fins because they are tilted upwards - go and look at an air-cooled engine and you will see what I mean)

I've only ever had one watercooled bike - keep it simple! When water cooling goes wrong it's a real pain, and on a small petrol engine it's just not necessary...

Tony

Pigford 7 Sep 2009 19:05

Water cooled (WC :innocent: ) has an advantage that you can get more performance out of an engine per cc, compared with air cooled (AC).

But this should not be a major consideration for a touring/adventure bike.

WC add extra weight, extra complication & extra fragility :nono:

AC will be more tolerant to high temps, as a WC engine will boil over... and after all, a WC motor needs AIR to cool it anyhow :rolleyes2:

Although I suppose you can make a quick cuppa a bit easier when you finish you trip with a WC bike :blushing:

Pays yer money & makes yer choice.

colebatch 17 May 2011 12:39

Quote:

Originally Posted by Michael_London (Post 242964)
if you sit stationary for long periods of time with the engine running then the engine will gradually just get hotter and hotter as no air is passing by the engine - is this correct?

No ... as an air cooled engine gets hotter, it will transfer more heat to the surrounding air, as the temperature differential will be greater. The hotter the engine gets, the greater the temperature differential with the stationary air next to it ... and the greater that differential, the more energy in the form of heat will be transferred to that air. Eventually (as the engine gets hotter) the amount of heat being transferred to the air will be equal to the amount of heat being generated by the engine i.e. there will be an equilibrium temperature that if you left the bike idling, it would eventually reach. If the outside air was cold, i.e. it was sitting outside a starbucks in Tromso Norway, in the middle of winter, the equilibrium temp the bike would reach would be lower than if you left it idling in the Sahara in the middle of summer. Thats because the temperature differential between the idling engine and the air is greater at -30 C than at +50 C.

Quote:

Originally Posted by Pigford (Post 256144)
Water cooled (WC :innocent: ) has an advantage that you can get more performance out of an engine per cc, compared with air cooled (AC).

But this should not be a major consideration for a touring/adventure bike.

I disagree ... efficiency of an engine impacts on how much fuel to have to carry. That means less range, and more weight. So the efficiency of the engine is a major consideration point for me. An old air cooled, carbed bike which may be more than 30% less efficient than a modern water cooled fuel injected bike will have to carry 6-7 kgs more fuel for the same range.

Quote:

Originally Posted by Pigford (Post 256144)
WC add extra weight, extra complication & extra fragility :nono:

The water in a cooling system will weigh about 1.5 kgs. As opposed to the 6-7 kgs in extra fuel you carry on an aircooled bike of the same power. Sure the radiator has small amount of weight, but so do the metal cooling fins on an air cooled engine.

Realistically, compare the weight, power and efficiency of the BMW Rotax 800cc engine vs a BMW air cooled 1000 cc boxer engine (the last properly air cooled engines they made) ... its slightly lighter, 40% more powerful, and probably at least 40% more efficient too. The range on a 16 litre F800 would be about the same or more than 24 litres on a airhead boxer. Particularly in challenging conditions when range is critical.

I dont have a fancy radiator guard on my X-challenge yet dont consider it a fragile part of my bike ... Come to think of it, I have not had a radiator or water cooling related problem in nearly 20 years of adventure motorcycling. The air cooled engine thing is a red herring. Its one of the great adventure motorcycling "wives tales" that is just not borne out by reality. I dont recall reading about anyone on the HUBB who needed help because his radiator got holed. Even if there was the odd rare case, fixing a holed radiator is something that you could get done is pretty much any 3rd world village anyway.

If you happen to love old air cooled engines, then by all means use them. I know plenty of boxer enthusiasts whose preference is not to ride anything different because they love the character. Choosing them for character is one thing, or to choose a bike that you like that happens to be air cooled ... great , by all means take an air cooled engine. Nothing wrong with it.

But its ludditeism and just closing eyes to the reality to suggest that old air cooled engines are better than water cooled, fuel injected engines for adventure bike travel.

Threewheelbonnie 17 May 2011 17:05

With a sidecar, traffic and terrain can mean high power at low speeds. We also carry tools, so get to meet the ones that don't make it:(

IMHO the technology doesn't matter, it's the quality of the bike and how well maintained. After a Rotax related walk I avoided watercooled for ten years, but the K100 suits my purposes now. So what overheats:

Bonneville- oil cooled - never

MZ - Aircooled - Never

K100 - water cooled - never

F650 - water cooled - after the load bearing lip seal went and after the fan switch stuck.

Enfield Bullet - Air Cooled - Timing was out.

Ural - Air Cooled - running on one cylinder due to electrical fault.

Ducati- Oil cooled - race clutch in the queue out of a GP meet.

R1150GS - oil cooled - had no oil in it (owner was confused by the concept, Touratech didn't sell him any, was too busy having a temper tantrum to be helped :rolleyes2:).

The F650 is bad design. The Enfield is a combination of old design and inexperienced owner. The Ural is poor quality. The Ducati is the wrong technology. The R1150GS was a stupid owner. If Ural had tried to make a waterpump in 2000 it would probably have been a poor copy of the Rotax POS. Solution: avoid Rotax and Ural. The others were just the wrong bikes with the wrong owners in the wrong place.

I don't think you can say watercooled good/air cooled bad or the other way round, they all work when working and require next to modification in how you ride if designed for road use.

Andy

bantam_1954 1 Sep 2011 21:31

Water cooling is a fairly modern thing to motorcycles so all those thousands upon thousands of miles covered by air cooled engines in that past answer the post very well . Simplicity is the by-word when touring.

shu... 1 Sep 2011 22:57

Quote:

Originally Posted by Michael_London (Post 242964)

Will you get more heat given off, as in will you feel more heat coming from the engine as you sit on bike with an air cooled engine vs water cooled?

Not to get into the air-cooled vs water cooled debate, I can reply to this question. The answer is: it depends.

The hottest bike I ever owned was a water cooled BMW K100RS. When the cooling fan came on (especially when stopped) it was designed to direct the heat from the engine directly onto the rider, especially the rider's left leg (as I recall). That bike would cook its rider on a hot day. I never experienced that kind of heat with my air cooled BMW airheads (R75/5, R100RS) or my suzuki DR650 (oil and air-cooled.)

At one point, I think Honda tried to address this issue on the water cooled Goldwing by having the cooling fan reverse when stopped- to try to suck the heat off the engine forwards, but I think they gave up quickly on that when their new bikes began overheating.

Some bikes are notoriously hot and others don't seem to be.

...........shu

oldbmw 1 Sep 2011 23:03

Quote:

Originally Posted by bantam_1954 (Post 347768)
Water cooling is a fairly modern thing to motorcycles so all those thousands upon thousands of miles covered by air cooled engines in that past answer the post very well . Simplicity is the by-word when touring.

I just love these generalisations :)

Ahem ! Scot has been using water cooling for its motorcycles since 1926, I guess that makes my Enfield old fashioned :(

Or could it just be that water cooling isn't really that modern ?

As for the temperature differential equalising! just try leaving your water cooled bike idling with the fan disconnected then see if the temperature will equalise between radiator and ambient air.

gixxer.rob 2 Sep 2011 05:46

Water cooling of motors is a performance addition. Its idea is that with the correct sized radiator in a given ambient temperature range it will keep a motor in the "sweet spot" thermally this in turn gives more HP for a longer period of time at a particular level. Some water cooling is tuned more than others. Have you seen the masked off radiators that used in MotoGP, they are trying to keep the motor at a certain temp range.

I am not sure about the theory that the bike temp will reach a balance with the outside air. Its got to do with how heat is generated by the engine internals and surface area to get rid of the heat. You leave an air cooled bike idling in 30c it will cook it's self eventually, because a point will be reached that surface area or the fins cannot radiate the heat quicker than the engine internals generate. Throw in the fact that the oil will also eventually get too hot and loose its ability to both lube and carry heat away..

But all of this bad stuff will take a long time. A long time.


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