Have a 1974 disel 580 B which I bought a year ago and only has 1574 original hours on it. The temp. gauge is colored orange, green, and red. It has always run between yellow and green, or sometimes a little on the green side. However, the last few weeks after 10 minutes or so it has started to go to between green and red (showing hotter than usual); sometimes a little to the red side.
I have taken the raditor cap off when the needle shows hot, but I don't get that steamy excessive pressure, no boiling water.
What should I start checking first???????
Thank you inadvance for your assistance. David