Universal M35 water temperature gauge issues

I have a 1988 Universal M35 with a Novatron engine panel. This season has presented me with issues with the readings of the coolant/water temperature gauge. I have undertaken a litany of steps to incrementally rule out sources of the problem including replacement of the coolant, the coolant thermostat and temperature sender, checked and cleaned out the heat exchanger, and a host of electrical tests today on the gauge itself as per the Universal manual and Nigel Calder. Unfortunately, the identical replacement gauge is no longer available. Rather than lay all this info out in detail, I would appreciate if a member very familiar with the engine, engine panel and gauges would contact me at my email address off-line.

Ken Dakin
NS33 #7
Sashay
Kingston

Hi Ken,
Have you checked the water pump impeller?
Nick
N30U
Purrfection
Collins Bay Marina