Freightliner M2 - Cummins ISC Coolant Temp Fluctuation

Hi, I just purchased a 2012 Freightliner M2 106 dump truck with Cummins ISC 8.3L, 10 spd. It has 25k on the odometer, and I have been experiencing coolant temp fluctuation from 175-200 F. This does not appear normal.

Background:
After initial start/warm up and as I get to highway speed (55-60 mph), the coolant temp keeps rising up to 230 F and the clutch fan kicks-on w/ the check engine light (this happens frequently during initial start). I let the truck coast in neutral when this happens, and then the temp decreases to 175 F, rather quickly within ~10 secs).

Afterwards, the coolant temp steadily increases from 175 F to 200 F and back down to 175 F. I see this continuous cycle every few mins. Coolant temp is steady (~180 F) when idling after running for hours.

Here is the following fixes I have attempted so far:
1) I pressure washed the front condensor, radiator, and intercooler as best as I can. Minor debris/dirt found.
2) I replaced the temp sensor and thermostat (180 F) with factory parts

Any thoughts on symptom? Is this normal operations? What else could be the issue? I called both Freightliner and Cummins technical assistance for feedback but they were uncertain and recommended to bring into dealer for inspection.

P.S.: The coolant expansion tank is to the full mark and there is a slight coolant drip near the cap. Not sure what is the issue here (potentially air in the system?). What is the proper procedure to bleed the coolant system?

 

Thank you for all your inputs. So I took a closer examination of the expansion tank today to see if there was any clogging within the hoses. There was none but the pressure cap seemed dirty around the vent so I cleaned this out with an air compressor.


Seems like the truck is running a lot cooler. Not too sure if this is the result of the cap or the thermostat now working within it's nominal range but the temperature is more consistent, staying around 180 F.