Datsun Roadster Forum-311s.org

Its fine to monitor water temp, but you can cook the engine and still be reading cool with the setup you are showing. The 240 guys
are using that to monitor water temp for the ECU or to turn on a fan, not cylinder head temp.

I agree with you that the OEM gauge is not very specific, but it will show a catastrophe in progress if it works as designed.
Its also not really THAT hard to fix the sensor. Much easier with he head off the engine so you can put in on a drill press or mill.
Any good machine shop can remove a damaged sensor from the head for 50$.

Perhaps the very best option is to install a GOOD mechanical gauge (SW) sender in the original position or at the rear of the head.
The SW's are so good you can watch the thermostat cycle. j

I had originally thought about the mech temp sender in stock position, assuming the old sender could be removed. But as I recall, the temp probe was too long to fit very well there. Of course there might be other senders that could work there that are smaller.
Linda