My Jeep is a 93 ZJ with the 5.2 V8. Changed my Thermostat last week because it stuck closed (I presume). Now if I drive it until it reaches operating temperature it just continues to climb in temperature until it hits 260. At that point I can see some coolant boiling and steam coming from the coolant temperature sensor on the front of the intake manifold so there is pressure in there for sure. I thought I might have had air in the system, so I removed the radiator cap and reservoir cap and let it run. No bubbles from anywhere and no visible movement in coolant in the radiator (Full, reservoir full). The upper radiator hose was hot as hell, but felt like it was full of air, not stiff at all. Lower radiator hose was a little stiffer but also felt like it was just full of air. What does this sound like to y'all? Could a blocked heater core cause coolant to not flow at all? I'm leaning toward water pump though. Planning on replacing the water pump and T-stat again when I'm off duty tonight to see if this solves my problem, but I figured I'd ask y'all for some ideas. I need this vehicle to be fixed tomorrow so I can post out... (Active duty Military)

 

A blocked heater core will only stop heat, not overall coolant flow.

 

That's what I thought, as it runs parallel to the cooling system.. so does that sound like water pump possibly?

 

could be. thats where id start, water pumps are cheap enough

 

Does it cool down as you drive? If so check to see if the fins on the radiator are not clogged

 

How many times has it hit 260*?

 

No visible coolant flow pump or plugged radiator ....