Heater only warm for 30 seconds.
 

This is a FYI rather than a question. I have a 97 ford f-150 4.6l motor. When I turned on the heater it only works for 30 seconds then gets cold. So here is whati did to find and fix problem.

Checked Blend door and actuator....Drilled hole in box and looked with camera.

Pressurized cooling system....Good.

Radiator cap was weak...replaced it. Did increase temperature but not long.

checked temp at heater hose and found difference in temp. ...

Found out that the hose behind the water pump is NOT the feeder line to the heater core...it's actually the suction side of the heater core. So found that my restriction is the smaller tube on the intake.

So how did I fix the blockage? Easy

I drained all the coolant out of the system. Spliced a "t" between firewall and the smaller tube that sits on top of the intake. Then took the Thermostat out. Ran water hose full blast for a few minutes. When you take the thermost out lease assy. loose for water to flow.

That's it. Works great now. Hope this helps.

PSS>! Just another FYI. I ran the heater for a little bit and the same condition returned. So after some thinking I realized that by putting the "t" on the pressure side I was essentially re-applying pressure to the same side of the Heater Core. So now I put another "t" on the other side of the heater core. However I blocked off the "t" so water would not go back to water pump and un-hooked the pressure side "t" and added a drain hose to it. So I just Flushed the Heater core the opposite direction of flow....And Now...It works great. So all the block scaling just stopped up the pressure side of the heater core....Just back flush it and it works.
Good Luck.

Good info...thanks for the share!

Added to original post so re-read it if you missed the changes.

I still had some problems with more scale stopping up the Heater Core. So I did another flush and added a in line filter. There are a few out there but harder to find. So I went to Tractor Supply and pic up a in line canister filter for a pressure washer. I installed two inlets for it. One side for a 5/8th hose and the other 3/4. I simply spliced it into the inlet side of the heater. I did have to add some hose on both side but it allowed me to position the canister out of the way.

Now if the flow gets slower I just unscrew the canister cap and rence. Works great now.