1997 Jimmy NO HEAT!

The heat has always worked fine until recently. Basically, I cant get any heat out of the vents. Truck coolant temp heats up fine. This summer I put in a new water pump and thermostat. The old pump went out. Prior to installing new pump I foward and reverse flushed the heater core and the entire cooling system. I have never had coolant consumption issues that I can remember.

How do I troubleshoot no heat?

Thanks all!

Update: I found relevant causes could be clogged heater core, bad thermostat, or blend doors not closing. I just flushed the core and its a new thermostat. Since the new waterpump and thermostat the truck does seem to get awfully hot (220+) when driving on the highway for long distances(50+ miles), which it never used to do. Any new ideas?

Try bleeding the heater core. With the engine running remove the upper heater hose and then refill the coolent.

Try bleeding the heater core. With the engine running remove the upper heater hose and then refill the coolent.

Ok, heres a little more. The blend door must be working as there is an abrupt change in sound and speed of the air moving when I turn the adjustment from cold to hot. I started the truck and allowed it to get up to running temp, checked the to/from line right next to the heater core and both were cool, I believe no coolant is getting to either! I started to release the radiator cap at this time and it started shooting, so it was pressurized at this time, so I would assume it hot.

What would cause this? From the looks of the waterpump design, it looks like the flow does not pass through the thermostat on its way to or from the heatercore so a bad stat shouldnt cause this right? So, did I install a bad waterpump?

Also note that the truck does start to over heat on long drives when driving on the freeway. It doesnt overheat if you not going fast, rush hour traffic it wont overheat.

Looks like the fan clutch is working fine as from startup it kicks in as it should and then kicks off.

It still sounds like you have air in your system. It is hard to get the air out. Start the engine cold and remove the highest hose to bleed out the air.