Okay so my truck keeps over heating. 05 1500 3.7L Figured it was the thermostat. Changed it. Still overheating. Took tstat out Returned got another checked this one first. It opened fine. Put it in truck.....still overheating. Poor water from both directions of top rad hose no clogs there. Poor through bottom and no clogs there. Poor into radiatir and it will drain out bottom. But still overheating. I take thermostat out and it doesn't over heat anymore. But I'm scared to drive it long without thermostat in there. When I took tstat out I looked into top of radiator from where the cap goes on and I can see some fluid circulating. Anyone have any idea what could be wrong with my truck? Any help please! And yes I was putting the thermostat in the correct way. Even to make sure I tried putting it in backward just to prove to myself I was putting it in the right way lol.

 

Water pump may be weak, fins could of worn away resulting in less pressure. Your coolant temp sensor could be bad also. Heater core could be plugged a bit too. Back flush system, and water pump would be my first steps, then sensor.

 

I second what NoLimitzR1 says. Had a car do this once, it was the coolant. It apparently was just old and degraded to the point it could not keep motor cooled properly.

 

Or you could have blown head gaskets

 

I replaced the radiator yesterday and rad hoses, and seems to be running fine. Drove it about 7 miles and had it running for 45 mins and it didnt get past the 1/2 mark on the temp gauge. hoping it keeps up and doesnt start acting up again.