My 05 is blowing cold air out of heater after it is warmed up. At an idle it blows hot but after you drive a few minutes it blows cold. Under accel it will also cool right off. Today driving home in the bitter cold, cruising on hiway, blowing ice cold I pulled over to check heater hoses. Ice Cold, yet temp gauge normal, degas normal no venting. HG's changed with studs, EGR cooler checked, new cooler, new injectors. Ongoing now for a couple years. No summer heating issues. Very Confused. Help. Could it be thermostat?

 

Maybe your heater core is bad.

 

Gauges have a lot of range in temp. without moving..This happened a couple yrs. ago in one of our ambulances. The thermostat was stuck open. Replaced and all was well...

 

A ODBII reader (ie: scangauge2, insight, etc.) can give you the actual
temp. The dash gauge is a very crude device 100 or 180 reads pretty
much the same thing.

If you could read the coolant temp you'd find a bad thermostat
because the temp would be below 190 once warmed up.

 

Thanks guys, I'm gonna try the t-stat on the weekend.

 

My vote is stuck open t-stat or blend-door faulty (I'm not sure if the blend-door is vacuum driven or mechanical). How does your top rad hose feel (hot/cool....solid/colapsed)?

 

Also check the vacum line on the heater control valve. They are known to get knocked off or leak vacum. Gray vacum line near the add oil spout.

 

That happend to me. turns out i was low on antifreeze. check it you might just be low.

 

Changed the t-stat tonite and now hot as he**. Thanks for all the help.

 

Great to hear.. Especially with winter coming on strong this year....

 

Hey guys I'm having issue with cold air just replaced t stat didn't change nothing..when I turn heater off of change to ac that heater control valves stays open what can I do to fix it...thanks

 

Could be a vacuum leak. Check heater control on heater hose above passenger side valve cover. See if you can move the lever by hand. Watch the control while an assistant turns on the heater to see if it moves and check the gray vacuum line with a vacuum gauge.if your not getting hot air the control is probably staying closed,I'd wire it open until the weather warms up and tackle it then.

 

Mine is blowing cold air only at idle. Any throttle setting above idle produces the proper heat. Vacuum issue?

 

Check vacuum pump, as well???

 

Yours doesnt sound like a vacuum problem to me. Check coolant level, possible reasons for yours is water pump impeller is broke, thermostat, blocked heater core, head gaskets.