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Radiator overflow tank behavior ?

7701 Views 12 Replies 7 Participants Last post by  Dirt_Dad
This was a new one for me. Riding 300+ miles home today from New York. Outside temps in the low 90s and I notice I'm seeing 3 bars on the temp gauge more than normal. I stop and I hear a gurgling sound. A check of the overflow tank shows the level about an inch or more over the full line.

About 3 minutes later I look again and the overflow tank is completely empty. Restart the bike and at speeds less than 50 MPH the gauge is always reading 3 bars. 50 and over it goes back to 2 bars.

I found some wet spots on the left of the crankcase and I assume my top hose is leaking. That's easy enough. I assume the gurgling is from air getting sucked into the hose.

The thing I'm confused about is the disappearing fluid in the overflow tank. Is that expected behavior? I witnessed this on two different stops. Is that just what happens when there is air in the system?
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It also specifically states to use OIL but I'm not sure why). Heat the oil, and monitor the conductivity of the thermoswitch with a multimeter. It should open (conduct) at approximately 208 degrees
If lived at an altitude of 2500' and tried this test it wouldn't work--the water would boil at 207.5°F.

Of course, using oil is a huge fire hazard. And if any water drops into the hot oil, the water drop will flash into steam and blow hot oil on to you--and the hot oil sticks on the skin and burns deep.
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