So mostly my engine temperature is at 180. But yesterday while coming home, after 2 hours of driving, it slowly creeped up to 200. It was pretty much flat since we were in Southern Florida. So, I watched it for about 2 hours and then it started to fluctuate between 180 and 200 and settled to 190. The antifreeze level is fine (I see the green in the little window).
I'm thinking it is a thermostat.
Could also be a bad sensor, bad gauge, bad ground, etc. Being cheap, I'd start with the things that don't cost any money first.
I just drove 100 or so miles in north Arkansas to Branson Mo. some pretty steep grades and switch backs with ice on some of the roads (shady spots). My engine tempts stayed at 200*. 190 to 200. I have an ISL 400 Cummins. Averaged 7.6mpg full tanks. Fuel and water and a weeks worth of beer and food.
On our 1998 U320, turning on the headlights makes the coolant temperature jump ten degrees.
Do you have a monitoring system? I use a simple ScangaugeD to get accurate readings.
It sounds normal to me the thermostat is only open fully at 180 degrees and some thermostats are 195 degrees an engine running between 180 to 200 is normal depending on the load the engine is under running at 190 I wouldn't even think twice about it the cheapest thing to change is the thermostat but check the water pump belt that it's not slipping or worn out clean the out side of the rad to make sure the air is flowing is good not a piece of cardboard or garbage That got behind the rad blocking the air flow my temperature gauge also changes about 10° when I turn the headlights even the fuel gauge move's ?
Rick,
The M-11 (your 320 has a M-11) has a direct drive water pump so no belt to worry over.
Mike
Come to think of it that is when the temperature went up, at dusk.