Motorwon't stay hot

[supernaut98]

Hi All I'm new to the forum and wanted to introduce my self and seek advice.
I have an 03 Liberty with the 3.7L. In August I replaced the radiator, thermostat and added coolant (prestone 50/50 mix) to get the system back up to full.
It ran fine till it was -11 out and it wouldnt produce heat and the motor wouldn't stay hot on long down hills 3-5miles.
I replaced the thermostat and topped off the coolant again with the prestone about two weeks ago. The motor gets hot, I'm getting heat (hasn't been colder than 20*F) but the motor still gets cold on long down hills and the heat goes away. Once I hit a flat section or up hill the motor heats up again and the heat is back.
Im hoping someone has experience with this problem and can offer tips for trouble shooting it.
Thanks.

 

[tommudd]

First thing is it sounds like you used the wrong coolant, the Prestone is not the correct type, Prestone 50/50 Premix is a OAT type
Only use HOAT coolant
Next it sounds like you've replaced the thermostat, but did you install it correctly? Easy to do, some have done that before. Could be the heater core partially blocked or the pump not circulating the coolant through while coasting down hill. Did it start right away doing this or was it after 5 miles 1000 miles or ??
Yours is kind of a different issue

 

[supernaut98]

I figured the coolant was wrong after reading a little. Im getting heat now so I dont think its the heater core. (Could be wrong)

When I replaced the thermostat the second time I made sure it was installed correctly, cant say for sure if it was the first time.
I didnt notice any problems for about 5 months mab 6,000 miles. It was on extremely cold days when it wouldn't heat up.
Could the wrong coolant cause this prob? Should I do the water pump when I flush the coolant?

 

[tjkj2002]

Let me guess your kicking it out of OD on those long down grades in your area? If so it's 100% normal and still normal if leaving in OD but not touching the gas.


The reason is the fuel is shut off so your engine is only pumping air which will cool it down.




Coming down the east side of Vail pass my KJ would go from 195 degrees to 110 degrees in 2 miles.