dont fix what isnt broken. a hair above and below isnt an issue. if it really bugs you install an oem, cummins, thermostat.

 

How old is the coolant (figure not too old since you changed the pimp/thermostat)?
How clean is the radiator itself? Remember when the puke bottle disappears oil will coat the radiator, bad.

 

Coolant is 2 years old and clean ad the day I put it in. Was put in after a flush

 

what is the PH level and NALCOOL levels? how dirty is the radiator by the breather bottle on the front of the engine?

 

I don't know the pH or nalcool. And are you taliking about the blow by bottle? If so it's pretty oily there I had to take the catch bottle off

 

that being oily is likely blowing into the radiator, and causing the radiator to plug up.....


the PH and NALCOOL are elements that determine coolant life expectancy. a heavy duty truck service station should sell a kit to check it. and additive to adjust it. if not....

https://www.fleetguard.com/pdfs/product_lit/emea_brochures/LI33030-GB.pdf
https://www.cumminsfiltration.com/pdfs/product_lit/emea_brochures/LI33021-GB.pdf
https://puredieselpower.com/product...l-coolant-additive-engine-block-cavitation-preventive-1-pint.html#/product/8524
Amazon.com: Fleetguard Coolant Analysis Test Kit CC2602A: Automotive

the first 2 links are information on adjusting coolant health, the 3rd is the NALCOOL, the 4th is the test strips. FleetGuard is cummins. they are filter line cummins makes.

 

If the oilled radiator is plugged it wont have the fluctuating tempS. They will rise in a hurry and STAY THERE as theres no HEAT TRANSFER. Id replace thermostat and flush coolant. But there again I have vehicles amd known vehicles with over 250k and had NEVER HAD a coolant flush and everything works 100% with run you outta the cab heat. Id put a months worths of wages on that one too !!! So, anyone who says change coolant,thermostat every 20k miles their pieing up a rope !!! Wasting ca$h...... I have friends that drive OTR trucks with almost 700k miles and zero problems. Coolant ph level is within check. Dont know where or how these people get off living by the mechanical "book".

 

there are those that live by the "dodge said this so it must be true" crowd that follow the schedule religiously. i myself subscribe to the school of thought, "if this was a n14 how would it be serviced." therefore, mine gets mobil 1 delvac 15w-40, and gets the PH and NALCOOL levels checked and adjusted as needed. seriously thought about adding a water filter so i knew it was always in check.....

 

This is probably what your radiator looks like if you didn't extend the hose down or do another mod to keep the vapor from slobbering all over the radiator and engine
Mopar1973Man's Dodge Cummins Articles - What Happens If You Keep The Stock Crankcase Vent

 

i ment to post that but forgot lol....

 

https://quickserve.cummins.com/qs3/pubsys2/xml/en/bulletin/3666132.html

found that on cummins website tonight actually.....

 

The the oil and dirt plugged external radiator core will cause the fluctuations on hills that way due to the varied load on the hills. All you have to do is look closely to check it. Did exactly that when mine was dirty that way.