Heater blows cold when idiling

[SavannahMac]

I purchased a 2006 F250 6.0 powerstroke with 12k on original motor. Noticed today that my heater is blowing cold when idiling but blows hot when driving. Any advice here for what I should be looking for or concerned with.

[psd_va]

first and easiest check is to make sure your coolant level is topped off high enough.

[250TUFF]

Or your heater core might be clogged. I think mine is and going to flush cooling system before it gets cold.


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[mhatlen]

Take a look at the heater control valve on top of pass valve cover and make sure its opening completely. Look at it to make sure its fully opening and closing

[kaya@bernhausen]

since the problem is at idle only, as mentioned, more than likely a clogged heater core. can try back flushing. sometimes it works. if not, it would need to be replaced

[lugnut]

my 04 has done it for the last 50,000 miles. no heat at idle. rev it to 1200 rpm and the heat would blow hot. i vc9 flushed it. and replaced the thermostat and water pump. still no heat. i have read on the forums that this is a sign of a bad head gasket. i just refused to believe that since my truck was running good and my coolant level never seemed to change.....much. well at 199,000 miles i just got my truck back from the shop yesterday with new head studs installed. it started to feel low on power up the hills and the degas bottle started showing a black slime inside. now my heater kicks out the heat at idle. no more of using gallons of washer fluid to defrost my windshield in the morning. i hope this is not your case. but just thought i'd tell you my story from the past few days. good luck