A friend bought this 280z recently from a guy in Georgia and the temp gauge is too low by my thinking after a hard drive, I'm guessing PO put a 160*F thermostat in.  My local Nissan dealer won't order in a thermostat but I found a Stant 195*F ,  wondering if it is worth a try?

I thought I had a spare 180* but can't put my hands on it.

Thanks

 

I'd start by verifying the actual coolant temperature. If it is too cold I'd pull the thermostat and give it the boiling water test. It could be stuck in the open position.

Does it have an aluminum rad by any chance?

55 minutes ago, zKars said:

Does it have an aluminum rad by any chance?

No it is the stock rad.

Does it sit there stable or move up and down with driving? 

I think 195 is recommended for your part of the world.  "Cold".

http://www.carpartsmanual.com/datsun/Z-1969-1978/engine-280z/cylinder-head/41

1 hour ago, Zed Head said:

Does it sit there stable or move up and down with driving? 

I'll find out tomorrow morning when I take it out for a drive.

It could be resistance in the contacts from the temp gauge sensor (usually yellow wire) to the gauge.

Check for corrosion at the thermostat housing connections.   Temp gauge sensor is normal a single bullet connector.