My '03 Ram 1500 5.7 Hemi 4wd keeps overheating. Replaced the water pump, thermostat, hoses, radiator, radiator cap, engine oil pressure sensor, ECT sensor and I'm about to put in a new fan clutch. Truck is still overheating. I've flushed the system twice. I pressure tested the cooling system after all the repairs and the new radiator cap was defective. I exchanged it and tested the new one before leaving the parts store. I pulled out the new thermostat and tested it too. It works like it should. When it overheats, it's acting like the thermostat isn't opening and the heater blows cool air. The upper hose gets too hot to touch and the lower is cool. It's like there's no flow. I was thinking heater core, but there's no moisture inside the cab and no dampness on passenger floor. I burp the system for quite a while and it seems like air keeps getting back into it somehow. I suspected maybe a blown head gasket so I did a combustion leak test and it was all good. I've found several threads with the same issue but have yet to find one that figured out the problem. Any suggestions? I don't know what else it could be. Thanks!!

 

I had the same behavior on my RAM... I installed the thermostat in reverse. Even though I doubled checked. I felt like a Dufus!

 

You've taken the usual steps to address overheating. There may be something unusual causing your overheating.
Did the overheating just start suddenly? Any event or maintenance that preceding the overheating?
Lots of causes for overheating, but since you have a hot upper rad hose and cool lower hose, we should start with cooling system.
I rec you remove the thermostat and fill radiator coolant to about 1/2 inch below full. Start the truck and observe the coolant, do you see it flowing?
Stop the engine, fill coolant to top and top off the overflow tank. Replace the rad cap and bring engine up to temperature. This should take a while and temp needle should be indicating to cool side of mid point on gauge. Keep an eye on coolant level and be sure to keep rad full and overflow tank near max level.
Be sure to keep radiator full to avoid overheating due to air in system. Hemis don't have the problem with coolant air bubbles that the 4.7 has, but still need attention.
Keep checking temps of upper and lower hoses. An infrared temp gun is handy here.
If truck overheats without thermostat then we go to next step of checking water pump and engine block for obstruction.