Water temperature issues/light flashing?

[benh999]

My g40 is running really well now, however yesterday the water light started flashing and the temp guage never got above 75 degrees no matter long she's been driven for.  The coolant is a disgusting brown colour and I am going to flush the system out however there is definitely antifreeze currently in there.

Any ideas what is going on?

[GR40]

Bad wiring? Faulty temperature valve?

[kwijibo_coupe]

Level a bit on the low side?