I have a 85 k-10 silverado with the same problam,mine was picking up the heat off the headers at the sending unit so I moved the sending unit to the intake manifold under the top hose on my edelbrock manifold,no change ,I switch out the gauge ,no change so the only other thing left was the printed board on the back of the panel,I switched that out and it was fixed.It runs about 195 degrees all day long even while plowing snow.Hope this helps.