:D I can answer that one while we are waiting to see if the manual is on-line anywhere...
There are two lights involved with engine temp: a blue one and a red one. The blue one remains lit as long as the operating temp of the engine is "low." This also keeps the auto transmission from shifting into 'overdrive' and if max heating is selected from the passenger compartment heater, it turns on an ELECTRICAL pre-heater for the air going through the passenger compartment heat/air conditioning system.
The red light comes on when the operating temp of the engine gets too high.
The owner's manual doesn't say what those temps are, IIRC, but in Section 10-4 of the service manual it *seems* to indicate the blue light should go off at 176... That sounds about right, but I just read 'em, I don't write 'em.
In Section 03-17 the thermostat should start opening at 176-183F and should be wide open at 205F from what I can tell. That matches the spec for the 'blue light.'
No indication I can find of what overtemp is...