05 Monaco Cummins 300 running warm to hot

[was_butnotnow]

At times gets a beeping when the Cummins 300 goes above 200 deg. Starts slow and gets louder at the temp goes up. A/C off and pulling Buick Encore on a dolly.
Had been on dusty road so washed the radiator. Seemed to help but later going in I 15 north in Utah starts running on the top edge of running hot. Doesn't stay hot but goes in and out with the load.
Fluid is 1/2 between the lines.
This is a new to me MH so no history.
Any ideas.
Looking for Cummins diesel service places and found one on our way north at Color Country Diesel in Cedar City UT,
Is there something I should try before I hand it off to a service center.
BTW I get no dash warning lights just the low and louder beeping as the temp goes up. Never gets above 225 deg. BTW daytime temp on the road 100 deg. Did the same things yesterday heading north to Kingman AZ in the heat. It does drop down when not under load.
Heading to Idaho as camp hosts for the summer.

[was_butnotnow]

I did a Google for a scanguage-D will look into that for sure....
Been pulling a 5er for 12 years a full-timer and now a DP and this is all new again. WOW
Thanks

[was_butnotnow]

Rear

[wolfe10]

Rear or side radiator?

[jplante4]

First of all, you need to get the actual coolant temp from the ECM. I can get my dash gauges to change by turning on the lights. A scanguage-D or something will get this data.

May be counter intuitive, but a higher RPM will aid in cooling, so maybe a downshift under load would be called for. Putting the RPM closer to the max power / torque rating will lower the stress on the engine and circulate the coolant faster removing more heat.

Honestly, I'd be happy with 225° on a 100° day.