01 SportTrac heat problem.

[jbarber18]

I have an 01 ST and recently (now that is getting cold out) I have noticed that my heat is not staying hot. I tested it at idle in the garage tonight, and it will go from hot to cold and back (about 5-10 sec cycle). I checked the heater control valve and it seems to be working ok. The temp gauge seems to stay at about 30% of the way up even after running on the highway for a while, so I am thinking maybe a bad thermostat, but if that was the case, wouldn't the heat just stay luke warm, not fluctuate? Some also mentioned a plugged heater core or blend valve issue, but neither make sense with the hot/cold cycle as it is. Anyone have any experience similar or other ideas? I hate to just start trying parts to try parts.

Thanks in advance all!!

 

[05dakotatrac]

i think you thermostat is shot bud.

 

[Markaprice73]

+1 thermostat may be stuck slightly open. It may be fluctuating because as the engine block heats the coolant to give you heat for a sec and the coolant is also slowly going to the rad to cool and cooler coolant goes back into the engine giving you no heat for a sec. Even if this is incorrect thinking. Its never a bad time to change a thermostat. Either way if you are able, back flushing the core is free and thermostats are cheap. Let us know any results.

 

[Markaprice73]

Also, air trapped in the cooling system can have this same effect. Has the cooling system been open for any reason lately? Any leaks?

 

[jbarber18]

New stat last night. No improvement. Temp gauge is about 35-40% and stable. Heat still alternates between hot and cold. I will try to flush the system and heater core this weekend. Until then, I'll keep my heavy coat and gloves on for the drive home!!

 

[ncranchero]

Blend door actuator

Check it for operation

 

[jbarber18]

Update

Ok, so I did the coolant flush tonight and that didn't help, although it probably was due so its done now. I checked the blend door actuator, and it seemed to work fine at first, but I realized that with it unplugged, the temp would stay constant whether hot or cold. So I took a little closer look. With the actuator in place, I watched the shaft and could see that with the selector on hot heat, it was moving back and forth causing the temp to fluctuate. Now here is my question: Does the actuator have a feedback loop internally to determine where it is positioned, or is that signal coming from the control module? If I had to guess, I would assume a closed loop system inside the actuator module but I'm wondering if someone knows for sure before I go buying parts.