Main wiring loom regulation

ok so swapped out the PRC7311 for a new AMR2631 and paired it up with a new PRC6663 sensor - I was thinkin that the engine temp of 73 degs was alittle cold especially as my landy is winterised with a wabasto diesel heater and radiators in the back , will put in a 84 degs thermostat and see how it goes -

New thermostat now in place (83 degs) an gauge pretty much in middle so happy with that - my next issue regarding gauges is with the oil temp gauge - I have replaced gauge with a new PRC7318, however the gauge never gets to more than 1/4 hot and thats only after a good run - I have been looking at replacing the sensor but the ones identified are PRC4372 (this one seems to be for 24v) and PRC2507 (this one is for a v8 petrol)
As always any advice would be great