It's an Autometer mechanical (capillary) gauge. Can't remember if I tested it in boiling water or not (think I did a long time ago). From the underhood heat and touching various cooling system parts, I think it's reading about right. I agree, 198 maximum is not too hot as long as it doesn't keep climbing, and I've got lots of oil pressure. But I would rather have it cooler as protection from detonation on pump gas. And the thermostat ideally would be the sole determinant of operating temperature...
Ambient temp varies a lot here, of course, but it's been doing this since I got it running four or five months ago (50F or 95F, same behavior).
I would check it with a pyrometer in several areas. Did you test the thermostat? Maybe it is opening at a higher temperature than the rated 180 degrees. One item I like is the ambient temperature does not seem to have any effect on running temperature. In reality if you were running a 195 stat the temperature may not be any different. So make sure that thermostat is right. One thing a pyrometer could tell you is the face temperature of the radiator core. If you have irregular readings it could indicate restrictions. Before I wasted any money on a radiator I would verify that thermostat and core temperatures.
