Hello, I'm new to the dodge world and I have a little issue with my cooling system 5.7 hemi. I've bled the system 3 times and it still is acting funky. There's normal heat in the truck and after running it for a while it starts to get hot and as soon as I turn the heat on it drops to normal operating temp and it stays normal the rest of the driving time. I don't think its the thermostat because both radiator hoses are about the same temp. There's no leaking around the housing or the water pump. I'm at a loss. Truck runs great other than this.

 

Likely culprits: thermostat, coolant, fan clutch.
Your upper radiator hose should be warmer than your lower hose, if they are same temp then thermostat may not be opening.
Coolant could be improperly mixed and have too much coolant and not enough water.
Faulty fan clutch would cause the fan to freewheel and not pull air.
Start with the thermostat, it's easy to do and cheap.
The heater core is acting like a mini radiator and cooling off your engine.

 

Cooling system is pretty simple:

• coolant
• Water pump
• radiator
• hoses
• thermostat
• radiator fan & fan clutch

If you gave more info we could help narrow down the problem
When does the heating happen? Low speed driving, highway? How many miles? Any idea of the cooling system maintenance history?

 

It happens at higher speeds i do a lot of highway driving. Im not sure on the cooling system history. I just bought the truck used last week with 159,000 miles on it. So I planned on flushing the radiator and changing thermostat tomorrow. But trucks been maintaining great temp until Friday I noticed it fluctuating more. How would I test a fan clutch?

 

From everything I've been researching i think i tested the fan clutch. When the engine was cold I rotated the blade by hand and with slight resistance it spun about 1 to 11/2 times. And I started the engine and shut it off and it rotated about 1 to 11/2 times. No slop in clutch. So guess I'll replace the thermostat and get some fresh coolant running through the truck.

 

when you say it gets hot, what do you mean and how are you measuring temperature?
where is the needle on the gauge?

My fan clutch passed the spin test and it was bad
When I removed it there was quite a bit of silicone fluid leaking on the back side where it bolts to the fan
A little bit of leakage is normal, but mine was dripping

Overheating at speed is usually radiator
Next most likely would be water pump

Less obvious problems is belt tension

 

The needle is how im reading the temp. But it starts to get to about 3/4 and stops when I turn the heat on it goes back down to right under 1/2.

 

If you're coolant looks nasty, ie its not clear and/or has particles suspended in it
your radiator could be clogged

Fresh coolant is a good start
Chrysler compatible coolant like Zerex G05 is highly recommended

 

If turning on the heater brings the temp down, that would suggest the radiator isn't being as efficient as it should. Start with a GOOD flush on the radiator, both directions. If that doesn't seem to make much difference, replace it.

 

If the fan spins 1.5x by hand, it sounds like the clutch is good. Furthermore, at highway speeds, the fan is barely needed as air is being pushed through the radiator. I would suspect the thermostat first, then the water pump. Minerals in tap water can cavitate metal water pump vanes, causing weak flow, even though no leaks are visible. As mentioned, It can be the radiator too, which might benefit from a having a flush run thru it, or replacement. Start with the cheapest, then stroll down the money lane till you find the fix.