While driving the car suddenly went into limp mode with high coolant temp.
i did the IPDM test and the fans kicked on fine
i did notice coolant was empty in the overflow.
guessing some hose broke?
Ideas on what might have broken?

 

check this thread, it may be related to the problem you are having.

https://www.myg37.com/forums/showthr...errerid=369648

 

Thanks, I had fixed the heater hose earlier so possibly something else

 

Miracles happen sometimes

I filled more coolant but this time I tightened the radiator cap more than I did last time and, would you believe it, the coolant leak vanished.

 

Miracles don't usually happen when it comes to car maintenance. If your radiator cap is more than eight years old, I recommend replacing it as a wear item. Once they stop holding pressure, the cap can get loose unpredictably.

 

When was the cap replaced?

Complex devices that most take for granted:

 

I replaced the cap. I did notice that on the old cap, I had to crank down hard for it to seal but the new cap sealed easily. I heard a pop and knew it sealed. Did not have to crank down on the cap.
Pressure is holding and no leaks