Water temp light and cooling fan problem

[rugguy]

A little history before the question:

A few weeks ago I managed to put a small crack in my radiator removing a damaged engine guard. I removed the radiator and took it to a well-known shop here in Atlanta where they welded it (yes, they knew it was aluminum), flushed it and did a pressure test. No leaks and all was fine.

Two weeks ago, after reinstalling the radiator and refilling the coolant, I was sitting in traffic when my water temp light came on. I noticed the cooling fan wasn't running. I immediately pulled over, let the engine cool down, the traffic subside and rode home without incident.

I tested the fan out by grounding the thermo switch sensor lead to the frame and the fan came on. I assumed the thermo switch had gone bad, either as a result of the radiator repair or just age, so I ordered a new one.

I replaced the switch today. I hit traffic (you always hit traffic in Atlanta) and the temp light came on again and the fan was not on. Again, pulled to the side, let the engine cool, then continued without a problem.

Question: does anyone have any idea why the fan will engage when grounding the lead, but won't when the temp rises...even though the thermo switch is new?

As always, any help is greatly appreciated.

[Gryphon Rider]

Assumptions:
1. The fan is good - grounding the lead that goes to the fan switch runs the fan.
2. The switch is good - because it's new.
3. The fuse is good - because the fan ran when grounded out.

Things not eliminated by the above assumptions:
1. The fan switch is improperly grounded - either sealant was used on the threads that prevents electrical continuity, or the radiator is not properly grounded to the bike frame.  I have no idea if the coolant conducts electricity well enough to provide a ground.
2. The temperature light is coming on prematurely - check the temperature with an infrared thermometer to eliminate or confirm this.

Other things you can do for the fun of it:
Test the old fan switch to see if it's good or not.

[sandy]

The early Valks have developed a problem with false high temp lights coming on. Find a thermo meter and measure the radiator temp where the top hose comes back from the engine. I've had false readings for 3-4 years. Someday I'll go in and replace the temp sensor or temp module.

[rugguy]

Gryphon Rider: You are the winner of the "Big Brain" award for today. I cranked the bike and rode it to operating temp. I then put it on the kickstand to idle to see if fan came on before temp light. Temp light came on first. I shut down bike. Then I turned the ignition on but did not start the bike. I took a piece of 12 gauge wire and grounded out the radiator to the frame and "voila", the fan came on. I would have replaced every darn sensor, wire and idiot light on the bike before I would have thought to test the radiator ground.

I am not sure why the radiator isn't properly grounded. But if I can't figure it out, grounding it is an easy fix.

Thanks again!!

[rugguy]

Quick fix until I have time to pull the radiator covers and hunt the problem.

[Misfit]

The radiator grounds to the frame. The bolt at the top of the radiator is the ground. Make sure the bolt is contacting the radiator frame with good contact.

[rugguy]

Misfit: Thanks. I will make the permanent repair this weekend....but for now the ghetto fix will work just fine. And nobody knows it's there but me....and whoever reads this thread.

[Misfit]

 

[Farther]

Gryphon Rider: You are the winner of the "Big Brain" award for today.

This happend way to often to be a coincidence.