Wow... that really is a stumper.
If you are getting air lock, after a very very short time the engine would get hot as hell as circulation stops while the pump cavitates if in fact the pump is actually cavitating. But you can get air lock in parts of the system even while the pump is pumping away too.
Sounds like you need to know two things. What the actual water temp is in the engine at the sensor when you go into the red, and at the same time if water is flowing at the sensor. The only way I can see doing it, is yanking the sensor outand see if coolant comes out. But if it is air locked at the time, you will have just relieved the air lock by doing that and coolant will probably fly out..... A catch 22.
Does it ever come back out of the red while you are riding it?
I am still betting on faulty sensor system. Or least I am hoping that is all it is....
Bubba in TX
2011 Voyager "Betty Clunker"
A bad day on a motorcycle is better than a good day in a car
Some people collect T-shirts
I actually ride
Voyager 1700 owners...
WRAP your pipes....
You will be glad you did...
Nye County Nevada
Motor Officer Retired
Blue Knights Texas 43