mo;

I doubt you can hurt the guage innards by connecting a "forgeign" sender...senders are simply temp variable resistors in the (under) 1K Ohm range ...you could certainly check the resistance with an ohmmeter...you can also compare senders (at ambient and in an elevated water bath) to see if they are compatible/interchangable.

It's too bad your having this issue with your cooling system...I'd (we'd all, I'm sure) be interested in the root cause/solution...I'm compiling a cooling system article at present and will certainly include any interesting findings...BTW when indicator is showing hot, what are temps of upper and lower rad hoses (obviously indicates if pump is pushing coolant through for heat shedding which is a good sign). ..have you burped out air?...trapped bubbles can cause uneven cooling/hotspots and other cooling system funkyness...

Good Hunting!