All,
My understanding of the red led temperature light is that it is related to coolant expansion tank level only.  It does not indicate a high water temperature, per se.

So, in my TIICo-convert, I have some funky indications going on in this warm weather.  

The temperature needle hovers river around the first line over the led.  This is higher than with my stock engine, but seems ok, considering the different engine.  When on the highway for 20 miles or so (and only when its warm/hot out), the red light will start to blink.  I keep a watchful eye on the temp needle at this point, watching for a rapid change.  Nothing, the temp needle stays in the same place.  After a while, unrelated to a change in load or speed, the red light will go out.

I'm confident that my coolant system does not have any air in it, I have bled it well.  The "top-off" tank is full to the "max" level, and that does not change.  The expansion tank is full whenever I look at it.  Even if I pull off the road with the blinking light and look at the expansion tank, if is still full.  There is the little ring of bubble at the top around the cap.

The "top-off" tank is full of straight water.  Could this blinking light be caused by the expansion tank being topped off by clean water.  The clean water might fool the sensor into thinking there is a low level.

Should I keep anti-freeze in the "top-off" tank?

Any other ideas?

Thanks.

Bob Spooner
East Haddam, CT