K100 at what outside temp does the aux fan come on when you are not moving?

[pinhead]

I was wondering what others with K100 bikes experience when they are idling without moving.  I have a 1985 KRT100 and have noticed that the auxiliary electric fan comes on whenever I am stuck in traffic for more than a minute.  It happens even when the temp outside is 55 F.   I dont remember it doing that but not sure.  Do others who have this bike have similar event where auxiliary fan comes on even when outside temperature is below 60 F?

[frankenduck]

That's "early."  Check dirty front of radiator and coolant level.

[The Mighty Gryphon]

When traveling at a brisk pace, the engine will be generating a fair bit of heat.  As long as you are moving there is enough airflow through the radiator to dispose of the heat into the air.

When you come to a stop, the heat in the engine components continues to be absorbed by the coolant, but with no air flow the heat transfer is reduced and the coolant temperature rises.  Normally, there is enough convection airflow through the radiator to keep the coolant from getting hot enough to prevent the fan from coming on.

As the Duck mentioned, if the fan is coming on in lower ambient temperatures it may be because the fins are clogged with dirt and bugs collected over the past 30+ years.  A good soak and a flush from the rear to the front of the radiator should remove most if not all the accumulated junk in the fins.

[pinhead]

I washed the radiator out from the back and changed coolant and still fan comes on at relatively low ambient temperatures.I have noticed that the last year  the fan would come on at lower and lower ambient temperatures.  Normal running years ago I dont remember the fan coming on unless it was over 90 F when I was stopped so I think a gradual thing is going on.

[The Mighty Gryphon]

Have you done a cooling system flush?  It is possible that the passages in the radiator are clogged with minerals preventing free flow of coolant.

It is also possible that the thermostat isn't opening fully to close off the radiator bypass.  Bypassing the radiator can reduce the cooling capacity gradually allowing the temperature to rise when the bike stops moving.

[pinhead]

yes I flushed the cooling system and changed coolant.  But I didnt check the thermostat.  Is there any way of testing the thermostat beyond taking it out?

[The Mighty Gryphon]

The classic thermostat test is to put it in a pan of water and bring the water to a boil on a stove.  A thermometer in the pan will let you monitor the temperature.

[Laitch]

The classic thermostat test is to put it in a pan of water and bring the water to a boil on a stove.  A thermometer in the pan will let you monitor the temperature.

If you want efficient usage of your energy supply, bring it back to a boil to cook some lobsters or crabs. Any slight residue of ethylene glycol will only impart a unique sweetness to the meat.

[frankenduck]

If you do pull the thermostat to test it then be extremely careful with the O-ring/gasket around the lip of it. They are really fragile and not sold as a separate part.

[Duckbubbles]

My '85 K100RS owners manual states that the fan cuts in at 103 deg. C or 217 deg. F. coolant temp, irrespective of outside air temp.  By that time, the thing is awfully hot.
What I did on mine was supply a separate ground to the fan motor controlled by a rocker switch.  If I see that I will be sitting for a while I turn on the fan early and the temp will stay pretty low (I installed an Autometer temp gauge).  The temp control unit in the electrical box under the seat controls grounding the fan circuit at the preset temp so the control unit still controls the fan normally but I have a bypass.

Frank

[daveson]

Is there any way of testing the thermostat beyond taking it out?

Another problem that can happen is that the thermostat can get stuck in the almost closed position. As a result it takes longer to heat up since it's not fully closed, and later can overheat since it's not fully open.

Haven't had coolant problems with my brick, but here are some checks with cars, some of which is relevant. If the thermostat is good it should be close to normal operating temperature after about five minutes or five miles.if say it takes half an hour, that's not looking good ( or with a car half an hour before the heater starts throwing out some heat) the coolant shouldn't be seen flowing until the thermostat opens,  the hose shouldn't get gradually warmer but after the thermostat opens, the hose should be harder to squeeze after the thermostat opens.

If you have a temperature gauge the needle should gradually rise. After let's say five minutes, if the needle drops down just a little, thats the thermostat opening.

[pinhead]

Another problem that can happen is that the thermostat can get stuck in the almost closed position. As a result it takes longer to heat up since it's not fully closed, and later can overheat since it's not fully open.

Haven't had coolant problems with my brick, but here are some checks with cars, some of which is relevant. If the thermostat is good it should be close to normal operating temperature after about five minutes or five miles.if say it takes half an hour, that's not looking good ( or with a car half an hour before the heater starts throwing out some heat) the coolant shouldn't be seen flowing until the thermostat opens,  the hose shouldn't get gradually warmer but after the thermostat opens, the hose should be harder to squeeze after the thermostat opens.

If you have a temperature gauge the needle should gradually rise. After let's say five minutes, if the needle drops down just a little, thats the thermostat opening.

  I will do a check on that.  thanks!

[sooprvylyn]

I stuck a fan bypass switch on both my k75 and my k1100.  its super easy to do that, and then you can just flip it on when you are not moving and sitting for a while.

If you do need to replace your thermostat, its super easy to do.  Just make sure you get the rubber seal for it when you buy the thermostat since its pretty hard to source on its own and your old one is likely shot.  A lot of cheaper options will not include this rubber seal.