Even after being fully warmed-up, the heater in my 2004 F350 6.0 doesn't put out any heat at idle. Within 5-10 seconds after driving down the road and getting the RPMs up, hot air finally comes out. Then after sitting at a light for a couple minutes, the heater blows cold air.

Any thoughts on the cause and the fix?

Thanks!

 

check your coolant level!

 

Poosible causes that I have seen:

Coolant level (as mentioned)
Slipping belt
Failing water pump
Failing thermostat

Start with checking the coolant level and inspecting the serpentine belt. Those are the easiest to inspect.

 

Most likely: failing thermostat.

Did you check temp gauge and is it low when you don't get cold air.

If not, if you have automatic temperature control, the problem is in the valve that regulates coolant flow.

 

Good input from all. Seems like I'll be fore-warned now when I take it to the mechanic.

Thanks!

 

I'll put my money on the water pump. It is a common issue on the earlier 6.0 PSD.

Well, low coolant is very common too, but a quick glance eliminates that.

 

Hey Guys does anyone know the outcome of this issue. (How was it repaired)

 

Blown Head Gasket, Oil Cooler clogged with sand (left over from casting the block?) and low water levels!

New oil cooler, machined heads, upgraded head bolts (160 ft-lbs) and some other little things.

Grand Total: $5,300

Please don't say I got bent over the chair.

 

Fuel consumption improved up 2.5 mpg, a little consolation!

 

Glad to hear a positive outcome. Better mileage means a lot these days. We're paying $3.18 a gallon here, bet it's even worse on your end of the world.

 

As I was scrolling through the thread I was going to post head gaskets - my 03 had all of the above stuff like yours done...
... on warranty though!