Hello all. I have a '99 4x4 that is having issues with the heater.

There is no coolant leaking in the passenger floor board (not a leaky heater core)

When i toggle the cold to hot switch and turn the fan to high, air blows through the system (blower still works), but just blows cold air.

When i do the above, it doesn't feel like fluid is moving through the inlet and outlet hoses from the engine to the heater core. Any ideas as to where the problem might be?

 

Remove the inlet/outlet hoses on the heater core and run a hose through your heater core on both sides until the water comes out clear. Your heater core is probably gunked up. Try that first. If it dosen't work we can go from there. This is by far the easiest thing to start with.

 

Another vote for a plugged heater core. Coolant should always flow through the core regardless of the request for heat inside.

 

thanks for the replies. i wont get around to this until friday or saturday.

hypothetical- i flush the core, core doesnt rupture, hoses are clear, core is clear, and it still blows cold.

What would be the problem in this event?

 

Let's wait and see what the situation actually is after the flushing.

 

I am having very similar problems other than I do not have 4X4. Any help would be great, kinda got it fixed before the real cold weather gets here.

At this point, I have no heat.

I let the truck run this morning at work and had the heat on with the fan set at 2 and held my hand on the line that should take coolant into the heater core, nothing. The line did not even get remotely warm.

Line that goes from intake to firewall is the one that feeds "in" and the one connected to the WP is the "return" correct? Not like it matters, neither line was hot.

...touch the upper radiator hose, quite hot.

Before this, it was kind of an intermittant problem. I couldn't get any heat in the morning, but on my way home I had good heat and it was getting quite warm inside the cab.

Nothing now, not even on the way home.

I flushed the system out less than a week ago and during the flush left the heater and fan turned on, I did get a bit of heat, but it faded.

Vehicle is not overheating, no coolant smells in the cab, level is good.

I put a new thermostat in less than 3 months ago.

The Intake Manifold gasket was replaced about that same time.

Going to grab a new Rad cap in the morning.

I flushed out the heater core not all that long ago either. I was actually quite surprised that I didn't get anything nasty at all. I hooked the hose up, turned it loose and clear water came right out.

Water Pump?

 

Did notice this as well:

Was looking around under the hood with the vehicle running.

I heard a hissing noise (sounds like a vacum leak) coming from around the edge of the brake booster. Ran my finger along the edge of booster and when I got to a specific spot, the sound was greatly reduced.

Could this have anything to do with the heat not working?

 

i had the problem too
the gate that shut the two was sticky and wouldnt switch to warm when i switched it like you guys and it would only blow cold... I cut open the access panel with a knife and the door still wouldnt work right even when i tried to move it so i stuck a screw in side panel holding the heated side open for the winter...