Rep Power: 0

recently swapped out my dx motor for a ex motor..it runs fine if i leave the heat on red, it dosent have to be blowing air it just has to be on red. as soon as i slide it down to blue my coolant temp goes up..i change the thermostat and did a flush. what is the problem??

 
Rep Power: 518

First thought is
low coolant level or air trapped in the cooling system.
They can trap air in the heater system easily if the coolant got that low, and an engine replacement job would do it.

Turn the heater on HOT and the fan on full blast. Is there great heat? Does it get hotter as the engine is revved up? Does it cool off when you let it idle?

 
Rep Power: 0

the heat is normal, it gets hott like it should and stays hot, it dosent go up n down.. you wouldnt even know there was a problem if you never take it off the red. so i have no idea.. i have heard about the trapped air and ive tried to burp it and still does it..im stumped!

 
Rep Power: 518

Well, when you have the heater (water valve) set on HEAT, you are adding antifreeze capacity to the cooling system.
That would probably send me in the direction of looking at the radiator for being inefficient.

Like maybe the radiator is plugged up in the core tubes, or restricted, undersized/too small for the engine, or something of the like.

Or even a thermostat that can't open wide enough. (You didn't stick it in there backwards, did you?)


Have you checked the accuracy of your temperature gauge?? Maybe it isn't correct.

 
Rep Power: 0

could be head gasket issue. Take off the coolant cover and run the engine, if you continue to see bubbles its coming from the combustion chamber leaking through the head gasket. There are additional tests to confirm this but its a good start.