Heater not blowing heat @ idle

[rvx290]

Basically what the title says, so just to narrow down what I DO know:

 

-Coolant is topped up

-Shouldn't be any air in the coolant lines as I bled it originally assuming that was the problem

-Heater works great while driving

-Car reaches normal operating temperature quickly, but doesnt overheat or run cool, so thermostat 'should' be fine? **but dealership is convinced thats the problem (which makes no sense to me unless thermostats work differently than they did in the past)

 

Any suggestions? Should I re-bleed the coolant lines or do a coolant flush maybe lines/heater core corroded & only allowing enough hot coolant to flow through at higher RPMs?

Maybe water pump is shot & only pumping enough coolant through the heater core at higher RPMs? (but if so wouldnt there be a higher chance that the car would be overheating?)

 

Driving me nuts, I am usually fairly handy when it comes to cars, this is my wifes 06 and everything works awesome except for this one recurring problem, dealership has been no help. Other than taking advantage of my wifes lack of automotive knowledge.

[FusionDiffusion]

First make sure the water pump belt is tight and in good condition on the right side of the engine. I don't think the thermostat is the problem either because you would be noticing long warm-up times driving down the highway (50+ mph). Starting the engine cold and driving down then driving down the highway at 60 mph the engine should be fully warm in 5 minutes or less with a good thermostat. The temp gauge itself is not linear, so your engine might be 20º too cold and the needle would still be pretty much in the middle of the range, so it's best to measure the temp electronically. If you have a '10 or later you don't need a tool, otherwise you will need to monitor the coolant temp through the OBD port. If the thermostat was stuck closed, you would have lots of heat and the engine would be slightly overheating. If the thermostat was stuck open, more flow would be diverted to the radiator and you might not get heat for a while until the coolant temp heats back up. BTW the heater core bypasses the thermostat completely so there should be flow through the heater core whenever the engine is running.

 

My best guess is that you have a partially clogged heater core. At idle there isn't enough pressure or flow to get enough coolant flowing through it. So you might try flushing it.

 

First of all, you should change your coolant at 5 years or 100,000 miles (whichever comes first) and then every 3 years or 50,000 miles thereafter. So if the coolant has never been flushed and you have a 2006? it needs to be done. If this is the case, I would pick up a bottle of Motorcaft or Zerex cooling system flush and flush the whole system. Follow the directions and remember to use distilled water for the final rinse. These flushes can knock crud loose and it ends up in the heater core so you need to flush the heater core separately after using them.

 

So for the heater core you will have to drain some coolant (or the flush water if you just did that) and take off the heater hoses. One is attached to the back of the thermostat housing I believe, and the other is attached to the front side of the water pump housing. You could also disconnect the hoses at the firewall, but I think those are harder to get to. Turn the heat on in the car, then get a garden hose and flush water through one hose and out the other. Catch the initial antifreeze so it doesn't go down the drain but once it flows clear you can just let it run down your driveway. As you do this, try pulsing the water flow on and off to knock loose more crud. Then reverse the direction of the flow with the other hose and keep switching directions until you don't see any more crud come out. If you have compressed air, you might try shooting some through both directions also. Turn down the regulator pressure to 20 psi at first so you don't blow a hose if you have a blockage. Some people also use an acid flush like CLR and let it soak in the core for about an hour to dissolve crud. Flush both ways for 10 minutes afterwards. This is corrosive to the metal in the core, and I would only do it if I was facing replacing the heater core. Blow out the all water or fill the core with new coolant mix (don't leave tap water in it), reconnect the hoses, fill up the coolant bottle, then purge the system after revving the engine. Make sure you are using the right coolant that meet's Ford's specifications (Motorcraft gold or specialty green depending or equivalent depending on MY). Sometimes you just can't clear all the blockage (the core might be 80% clogged but will still flow water in the clear 20%) and have to just replace the heater core which is a chore. :angry:

 

If that doesn't fix it and you're sure the thermostat working well, the next step would be to replace the water pump. Keep us posted.

[awdpath]

When topped up, make sure the cooled coolant is at the yellow "full" line. How did you "bred" the coolant lines?

 

I had this issue with my 2007 Fusion (3L) two years ago. Even though I can see the coolant in the pressurized coolant reservor, I ended up putting in an additional quart (1L) of mixed coolant.