Fan reversal

A problem experienced by some owners of the GL1800 Goldwing is overheating at slow speeds. At speeds ~15 mph or less the fans are used. These fans suck the air through the radiators and out the front of the bike. This presumably is for rider comfort. At speeds over 15 mph the fans are turned off because the incoming air and the forward-blowing fans pretty much cancel each other out resulting in poor airflow. However, at speeds in the range of 15-25 mph the incoming airflow is still insufficient for good cooling. Prolonged use at this speed (slow traffic, parades, creeping along) can cause the bike to run hotter or overheat (coolant puking). Going uphill, pulling a trailer, hauling a passenger, etc., makes the situation worse. The 2006 and newer Goldwings have larger fans and radiators to lessen this problem although I think it occasionally still happens. There was also an ECM update on the older GL1800s to richen the fuel mixture.

There's really nothing wrong with the engine running hotter than normal. All engines will do that when put under a large load. That said, I think there is an unsettling feeling about seeing the temperature guage going up and up towards the red. I know I don't like it...whether it's actually okay or not. Overheating...coolant puking...is bad. A mod some people do is reverse the fans so the fan-generated airflow is always out through the sides of the fairings to match the incoming air. People have gotten good results with this setup. I had my bike taken apart for other reasons so I decided to do the mod. It couldn't hurt anything.

People on the the GL1800riders forum like to argue the merits of reversing the fans. Here is a point I'd like to make...just reversing the fans isn't gonna gain you much. Reversed or not, your fans will still only work when the bike is going going 0-15 mph. You still have the poor airflow in the 15-25mph range that can cause rising temperatures. To get the full benefits of reversing the fans you have to have some way of making the fans run during this range, too. I installed a manual switch to control the fans. I think a secondary thermostat switch has been pondered by a person or two.

Update: After having this mod for four years I can say it's a very worthwhile mod (for me). When in a situation where the temperature starts to rise I can flip on the fans on and the temp will hold still (under extreme situations) or cause the temperature to drop. I can also keep the fans on longer than the ECU normally would and allow the bike to cool even more. I have a real temperature guage so I can see this happening.

Reversing the fans requires two steps: (1) reversing the fan blade assembly on the motor, and (2) reversing the wiring in the connector so the fan motor turns the opposite way. The motor is not physically reversed.


You can access the fan & radiators without removing this much but I had it all off anyway doing other things. I wanted to see how the bike is assembled and where everything goes. When you take this off the bike there's a lot less mystery about the bike.

Here the fan & radiators were removed without taking off the front plastic.


Here is the left side fan/radiator assembly off the bike. There are two bolts holding it on and one tab it sets in. I tested the setup to make sure it worked and that someone hadn't already reversed it. The fan puts out lots of air.


The stock setup has ~1/8" to 1/16" clearance between the fan blade assembly and housing bottom.


When the fan blade assembly is flipped it is now higher than the housing. If reassembled now it would hit the radiator. The fan housing needs shimmed away from the radiator.


I used two 1/4" washers on each mounting tab to regain the needed clearance. Three washers were too tall. I ran the fan to make sure it would not touch at speed. The stock bolts are too short to be used with the new shims. I bought new M6 x 1.0 x 1" bolts from Lowes. Use blue locktite on all the bolts.


The last thing to modify is the plug. Insert a small jeweler's screwdriver in the tab to release the wires and reinsert them reversed. Repeat for the other radiator/fan assembly. Reversing the fans is actually a pretty trivial project. It's getting to the fans that takes time.

I reinstalled the radiators, filled the bike with coolant, and let it idle until the fans kicked on. The fans blew the heat several feet to the sides of the bike, and I had no leaks.


Update 2011: Following a rear end collision I had to rebuild the bike, so I made the cooling system even more robust by adding larger radiators from a newer bike.

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