Heat will not get hot - please help

[james.oco]

I have a 95 Explorer XLT, 90,000 miles on it. As it's gotten cold, I've noticed that I have trouble getting much heat out of the climate control system. It gets luke-warm at best. I've read a lot about blend door issues, so I removed the actuator controlling it. Though it is tough to see much with a small mirror and a flashlight, it looks as though that the shaft that the actuator pin sits in is in tact. I then played around with the heat valve in the engine compartment. Generally, one of the hoses going into the firewall and connecting to the valve is hot, and the other one is not. When I push in on the valve to close it off, what air was luke-warm coming out of the vents immediately gets cold. So, I'm assuming that the valve is ok. The two remaining issues that I've considered are the thermostat and the heater core. A mechanic has told me that since the temp gauge on my dash peaks after the engine runs for a few minutes, and then drops off a bit, means that the thermostat is ok. I'm not sure if that's right or not. Any suggestions?

 

[aldive]

I would replace the thermostat.

Good luck ....

 

[james.oco]

I replaced the thermostat and heater control valve, and there was no change. I then hooked up a garden hose to the heater core output, in order to backflush it, and at first no water would pass through it. Eventually, what I'm assuming was a clog, broke free, and water filled with dark sediment came rushing out. After seeing this, I'd assumed that the heat would now work. And though it is better, it still isn't where it should be at. Shoud I assume that the heater core is still the issue, or could it be something else as well? I've ruled out the blend door, low-coolant level, thermostat, and heater control valve as potential issues.

 

[marragtop]

Flush the core again. Also, make sure you are getting good flow to the core.

 

[james.oco]

When flushing it, does it matter whether or not I hook up the hose to the input or output of the heater core? Also, should I be flushing some sort of coolant system treatment, like one from Prestone, through the core as I backflush it? Should I be worried about rupturing the heater core?