Reversing Radiator Fan Direction

milkmaster

milkmaster

Joined
Jun 20, 2005
Messages
106
Location
Murfreesboro, TN
Bike
2006 ST1300
The only time my fan for the radiator comes on is when I come to a stop at a red light etc. What would be wrong with swapping the direction of the fan to blow through the radiator towards the front instead of blowing that heat towards me? One would have to monitor for a time to make sure that the temperature still stayed within the safe zone of course. I was told that Gold Wings already do this below 20 MPH. I have not verified that story yet.
 
That might move some air, but only while stopped. I think that the blades of the fan are curved to maximize airflow the current flow direction; reversing their rotation is likely to move air very poorly. Let us know if you give it a try.
 
That's not the only time they come on, it's just the only time you notice it. Reversing the direction would only cause a burn-up of the switch/fuse or some component as the forward speed of the fan and the direction of the air when riding match and cause the fan to stop - like holding the blades. So, just something you have to deal with IMO.
 
BakerBoy said:
That might move some air, but only while stopped. I think that the blades of the fan are curved to maximize airflow the current flow direction; reversing their rotation is likely to move air very poorly. Let us know if you give it a try.
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I agree. The fan is designed to pull the air than to push it. If you bring everything in front of the radiator, then you may be able to achieve the same effect.
 
My idea came from watching my own radiators on other bikes and my neighbor's GW. I am going to look at his fans and see what differences and comparisons show me. Maybe I should have named the thread Reversing AIR flow and not just the fan direction. Not entirely the same concept.
 
You would loose some efficiency because you would be trying to cool the radiator by drawing warm to hot air out of the engine compartment instead of the cooler air outside it. The high "under hood" temperature is not solely due to the radiator, there's radiant heat from the engine and exhaust system too.
 
Reversing air flow might work when stopped, but when rolling at low speed, the net effect would be less airflow across the radiator. That would be bad. I would not recommend trying this.
 
Something to consider is how clean the rad is.
I was having trouble with temps when my speed was too low. I picked up a large bottle of Hydrogen Peroxide and put a small hole in the foil seal. The engine had cooled a bit and I squirted the Peroxide in every spot on the rads as I could on my wing. Should be cake to hit all the ST's rad. Flush from the inside after the bugs cook a bit.
You will be amazed how much crud comes out if the ST is anything like the wing.
 
I believe the 'Wing radiators are side mounted, so the fans would blow from inside out. When the bike is moving the low pressure created by airflow over then side fairing surfaces draw air through them with no fan assist needed.


Good Ridin'
slmjim
 
milkmaster said:
My idea came from watching my own radiators on other bikes and my neighbor's GW.
Click to expand...
Ah - that explains where you got the idea from.

The Gold Wing radiator fans do reverse direction, but only when the motorcycle is stopped or moving at speeds below 7 MPH. When it is moving faster than that, they operate in the same manner as the ST radiator fans. Honda put some thought (and a fair amount of electrical logic) into the 'low-speed reversing fan behaviour' on the Gold Wings.

Michael
 
This reminds of a funny story,a customer brings his car into my shop overheating after he had done his own repairs.It only overheated at 30 mph and above,at idle it was fine.So I open the hood run the engine does not overheat,so as I'm standing in front of the car my crotch is overheating.He put the wrong fan on,reverse rotation,so at speed there was no air flow through the rad.
 
U want the FAN to DRAW cool air from in front of the bike thru the Radiator, NOT blow hot air from the Engine block & Headers over the radiator.
The fan just keeps the same airflow going in stop & go, as if the bike were moving.
I think It'd get a LOT hotter under there if the fan was reversed.
 
Keep in mind those bikes that push air outward through the radiator with the fan usually have side mounted radiators and some kind of scoop that directs cool air from the front of the bike to the inside of the radiator. In all cases the fan should supplement the normal direction of airflow that occurs when the bike is in motion.

I'll bet that car that was overheating at only 30MPH was because the fan was precisely cancelling air flow at just that speed, i.e. zero air flow across the radiator.


-Jeff
 
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