New to Me 1997 32 foot CC Allure Question

[suzygirl2017]

I have owned this coach for 4 weeks now and have just completed a 3000 mile trip. The engine is the Cummins 8.3 electronic injection 325 hp with 74,000 miles on it. I am very pleased with the coach but have one concern. when we start out in the morning it takes about 20 minutes for the engine to reach 210 degree engine temperature and then about one hour later it falls back to 180 degree engine temperature and stays there all day, steep grades still stays at 180 degrees. The last leg of our trip I topped up the coolant reservour and once the engine reached 210 degree it fell back within minutes to the 180 degrees and stayed there for the rest of the day.

Question - is it normal to take a hour to drop back to 180 degree after reaching 210 degrees or should it be much sooner like it did on our last travel day?
If this is not normal would this indicate a lazy coolant thermostat ?

Thanks in advance for your input.

Dennis

[SeaDo]

Dennis
I have the exact same coach as you...
Mine warms up very slowly if it is sitting at idle, to warm it up within 4 or 5 minutes it has to be driven a couple of miles to get to operating temp. (also 180*)
However mine stays with a degree or 2 of 180 even in hot weather.
You may be correct that the thermostat might be sticky.
Let me know if there is anything I can help you with, I have had mine since 2010 and have put on just over 70k miles since purchase.