2004 v6 with no heat! ouch.

[Methodical]

Started my 4runner last night when it was -20 and no heat after a complete warm up. Fan is running fine, engine warmed up fine, and when I put my hands on the heater core lines, they are cold. Can my heater core really be plugged up? It was working perfectly before, and now nothing? Do they really plug up that fast?

Is there any other explanation?

 

[Methodical]

I put the car into a garage last night and when I pulled it out in the morning, heat was working as normal.

Any ideas?
Got 100k+ miles and my coolant pump is weeping, so it's time to replace it. But considering that the engine warms up and works fine, could it be the problem? No play in the fan.

The only thing I can think of is an air bubble in the heating hoses, possibly air coming in from the pump. But shouldn't the air work itself out when the engine is at running temps? and why would garaging it for a night resolve it?

 

[Kmvreter]

... Any ideas?
... my coolant pump is weeping, so it's time to replace it...

If you have a slow coolant leak then what's the current coolant level? Any coolant in your overflow tank? Low level will cause heat issues and eventually cost you an engine. Get the pump fixed.

 

[DaveS]

Do you have a block heater? The first one I had installed was bad and caused this issue for some odd reason.