So back in September my 2017 ram 2500 6.4 hemi started over heating building pressure in the system in the main hose that goes from the top driver side of the radiator to the thermostat housing. Had it towed to dealer ship they diagnosed it called me after working on it for 3 hours and said nothing wrong could be found and the truck was operating just fine?!?! They couldn’t find nothing wrong with it saying it would get to 224 degrees the fan would kick on and go back down to 210…. So I picked it up paid the bill and it’s been fine till yesterday. And it’s doing the same thing. There is no milky oil the antifreeze looks fine and is up to the cool max line on the reservoir? I’m completely stumped since December of 2022 the thermostat has been changed the radiator has been changed everything except for the heater core has been changed. I did notice last February that I was getting little to no heat through the vents could this be the problem would flushing the heater ore do the trick? Tia

The cooling system is SUPPOSED to build pressure..... higher the pressure, the higher the boiling point of the coolant. Should operate right around 18 PSI or so.

No heat is generally an indication of being low on coolant, or, a failing water pump.....

well yes the system is suppose to build pressure but the hoses are rock solid like there is a blockage. It’s not allowing anything to reach the block to cool it down. Is there anyway todo a test on anything to see where the block is at?

Is the engine overheating? How old is the thermostat? How old is the water pump? Miles on it??

yes it gets to about 240 while in idle I’m sure it would get hotter but I shut it off before it does get any hotter. The water pump is only about 2 years old had it done when it was traded in before I bought it from the dealer the thermostat is about a year old and it has about 150xxx miles on it.
also I figure I should add I have only put about 15k miles on it since I bought it since I drive about 10 miles a week back and forth to my semi on Monday and Friday and have driven it from central Illinois to Houston texas about 6 times so I’ve put very low mileage on it since I’ve owned it.

Bad coolant reservoir cap???

Overheating at idle? How is the fan clutch? (does it even have one?) Is there an auxiliary electric fan as well? Radiator cap is also a good suggestion.

Are you losing any coolant?