2002 Windstar Limited Heat Issues

[KzooFordGuy]

Hi Everybody, it's been a while since I have logged on but you guys helped me before and I have a new issue. The heat on my 2002 Windstar is not working properly and I have taken several steps to try and narrow down what's happening. Here are the details:

1. Both the front and rear heater cores have been replaced with new ones. The coolant was really nasty looking when I bought the van several years ago so I decided to go ahead and replace both of them. I flushed the entire system thoroughly before replacing them.

2. The thermostat and gasket were both replaced.

3. The blend door actuator is working properly and the blend door itself seems to be working properly.

4. Air goes where it is supposed to be going. There are no issues with which vents it is coming out of.

5. Temperature selector slide seems to be working. A/C works great!

6. Van does not overheat and gets warm as it should; after a few minutes from starting the temperature gauge reads about half way between Hot and Cold.

7. The main problem seems to be stemming from hot coolant not flowing through the heater cores at idle or low RPM. I can get it to work just fine if I rev the engine at idle or turn off the overdrive while driving to force RPM increase. Anything above 2500 RPM (when the engine is warm) and I can get it to work fine. When I slow the engine RPM or stop and idle, air gradually cools as I assume hot coolant stops flowing through the heater cores.

I am wondering what could be the likely causes of impeded coolant flow at low RPM? Air in the lines somehow? Some sort of obstruction that flushing and replacing the heater cores did not resolve? Is it possible for a water pump to fail to deliver pressure at low RPM somehow?

If the problem is likely air in the lines, what is the best way to find out where it is coming from?

[wiswind]

The heater core on the windstar has coolant flowing through it all the time.
Temperature control is done by the "blend" door that determines how much of the air will travel over the hot heater core.
You seem to know this....but want to review it for others viewing this thread, as well as keeping the focus on the heater core temperature vs air flow.

Note, that this is assuming that the fan is not significantly slowing down at low RPM......although, I would expect that if that were the case......to much extent.....then you would have other issues due to low voltage.

My windstar did not have the rear heat unit....so I am not familiar with that.
It is possible that there is air in the system that needs to be "burped" out.....
I don't know how to do this.
I have had air in the engine part of the cooling system....which causes the temperature to fluctuate way hot.....but you do not seem to be having that issue.

When the engine is COLD.....remove the radiator cap (if they still had one in the 2002).....and see if you are low on coolant in the radiator........which is possible (was on my '96).
If so....verify that the cap seal and the area in the radiator "neck" where the cap seal seats is clean (free of grit/dirt).
Then fill the radiator fully.....up to the cap...and put the cap back on.

Another thing to check....with the engine warm.......being careful to not get burnt (wear a glove).....squeeze the upper radiator hose.......is it firm (indicating that there is pressure in the system?).
If it is not firm....your problem may be that they system is not holding pressure....and you will need to find the source of that. (Cap.....on radiator or on overflow bottle, if there is not one on the radiator).

Also, verify that you have antifreeze in the water in the amount that you need .....between 50% and 70%.
Over 70% is not good......under 50% is not good.
You can get a coolant tester at most auto part stores.

[KzooFordGuy]

Update:

I believe that I have eliminated air in the system as the culprit. With the engine warm I ran about 3000 RPM until I had good heat blowing and I made a sort of adapter for my strongest shop vac to draw vacuum on the overflow bottle while the engine was running. Be careful if you do this! It worked a little too well!. I imagine that if you didn't pay super close attention you could suck hot coolant out and possibly burn yourself. I just used the shop vac suction to draw vacuum for several cycles on the overflow tank until I didn't see any bubbles. I never really saw significant bubbles to begin with and even after I was sure no air was present in the coolant, this did not eliminate the problem.

Next step:

Only thing left to do is verify that water pump has appropriate discharge pressure. I will feel the hoses, etc. for pressure under various conditions first before I go ahead and take the water pump off. I need to check the condition of the impeller. My best guess right now is that the impeller may be eaten up with corrosion and the water pump just doesn't develop sufficient head (pressure) at low RPM or idle to overcome the fluid friction of the heater core loop. It just keeps enough flow going to keep the car from overheating right now.

I'll let you know what I find out.