temp gauge reads high due to ground problem?
I have a '91 E150 that for some time now (i.e., years) has had a temperature gauge that reads abnormally high. I have replaced sensors, voltage regulators and the gauge itself in the past and gotten better results for a time, then it seemed like it would deteriorate, re-exhibiting the problem. It has gotten to the point now that normally the gauge consistently reads just barely below the diagonal slant of the temperature line, just before H.
Question 1: is there a known problem with gauges, particulary the temperature gauge, reading high due to a poor grounding situation that exists between the instrument cluster and the battery?
Question 2: If the answer to 1 is yes, is the temperature gauge particularly affected because it is the lowest impedance sensor, and therefore provides the best alternative ground for the instrument cluster?
We recently went on a long trip through the hills/mountains of Nevada across I-80. At one point the gauge bumped up against H. I pulled over and, after about 2 minutes, checked the radiator. It was warm to the touch, but not anything even close to overheating.
I recently replaced the ground cable from the battery to the chassis/motor with a stock cable from Ford. It was after this I noticed that the temperature indication would ride consistently very high.
Any inputs, before I tear into my dash board yet again, would be greratly appreciated.