1997 Ford F150 - No heat!

Hey Everyone!

I’m at my wits end with my truck - let me tell you the story of my people.

I purchased a 1997 Ford F150 with ~150k miles from a private party on CraigsList. Total price was $3,000.

After the heat left and the cold came I noticed that the heat did not work, at all. When the knob was turned all the way up the air that blew was ice cold, very similar to having the AC turned on (which works great.)

I enlisted the assistance of my father and we performed the following steps to identify/troubleshoot the issue, to no avail:

  • Flushed & Back flushed the system (used the hose adapter from Auto Zone)
  • Placed fresh coolant in the tank
  • Verified that the blend door is working great (also manually held it open, still no heat)
  • Replaced the thermostat

Some ways into this process we noted that the top hose leading into the radiator gets very warm, as it should. However, the hose on the bottom of the radiator leading away from it and back into the system is not getting warm at all. It is cool to the touch / ambient temperature. I am not sure that this is a critical piece of information but I seem to think in my head the hose coming OUT of the radiator back into the system should be a little warmer than ambient temp.

Any suggestions/ideas/hair brain ideas that may work would be greatly appreciated. Even in North Carolina 30 degrees is COLD.

Did you flush out the heater core separately? If you didn’t you NEED to flush it out with a water nozzle on the “jet” setting. Flush it from both sides, until you have a strong, clean flow.

I will assume one heater hose is hot, while the other isn’t?

I have repaired MANY plugged heater cores by flushing them.

Since you’ve replace the thermostat and verified that the blend door is working, that leaves the heater core, IMO

Thanks DB4690 - Will give that a go tomorrow and see what I get. We did not flush the heater core separately, just used the hose attachment where the 2 hoses enter through the fire wall.

@TrickyP Hold on . . . you’re not thinking of removing the heater core and flushing it, are you?

Those two pipes sticking out of the firewall are the inlet and outlet pipes of the heater core. Remove both hoses, stick that water nozzle in there and use the “jet” setting.

I hope this has been helpful.

One thing that is easy to do is touch both of those firewall hoses and see how warm they are. If one is very hot but the other is coolish, it’s an indication coolant isn’t flowing through the heater core. I expect you’ll find this to be the case. Could be caused by a plugged heater core, or that the valve which controls the heater core flow isn’t working properly. That’s the valve you control by turning the heat control from cooler to hotter.

BEFORE you go flushing the heater core…focus on air pockets in your cooling system…the COLD lower rad hose is definitely a BIG CLUE of this, and it cannot be caused by a clogged heater core.

I have had to replace more clogged radiators in my time than Id like to admit to…because they DO go bad. …however a clogged Rad would cause overheating…NOT a cold lower hose.

Make sure you do NOT have a huge air bubble in your system…SOME vehicles will not allow you to fully fill up the engine block with coolant simply by adding coolant into the rad…OR WORSE a side tank. I have LITERALLY had to remove the top rad hose at the engine…AND the thermostat…and pour coolant straight into the block until i could see it at the thermostat junction…and THEN …top off the radiator…then I had both rad hoses running HOT…as they SHOULD BE DOING. IN fact after filling the block at the thermostat housing…I then pull the top rad hose off the rad AND FILL IT ALSO… That usually does the trick… if your rad is clogged…the engine will overheat…and your heat would be HOT HOT HOT… The system needs to be air bubble free or it cannot move the coolant…as the “pump” is only a circulation pump…not a pump that can draw a column of fluid up a vertical pipe…understand this? Trust me…work on the air pockets that you have first… this is your issue in my opinion.

I would look into A possible air bubble…filling the block…the top rad hose etc, before more flushes… Should you suspect a clogged rad? I.E…was engine filled with rusty water or some such thing? If so…rad could be clogged, but that would only cause overheating of the engine…NOT a cold lower hose.

…go the route of getting out the air bubbles first…they occur when you severely drain the system…not always so easy to simply refill…

Laugh all you like…but I been doing this 27yrs now…and had to manually fill more blocks than I’d like to recall especially after a thorough draining because you cant burp huge air bubbles out very easily…and if you dont…then you dont get coolant circulation…I.e. cold lower hose and NO Heat


@db4690 Turns out those two hoses at the firewall were what we flushed with the hose - so all good there.

@Honda Blackbird Thanks for the thorough response, I will take care of any air pockets in the system and let you know how it turns out.

Wanted to update everyone on the happenings here. Sorry it’s been so long - been chasing down misfires for a few weekends.

After repeated flushings/burpings of the coolant system, I still had no heat. After doing a bit more research we decided that a clogged heater core was the ONLY option left. [Note: we replaced the water pump, which had fins that were rusted completely flat.]

We took the truck to a local do-it-yourself car wash and cut both hoses leading into the firewall - creating a closed loop going into and out of the heater core. We inserted the pressure wand into one of the hoses, clamped it down and had at it - and blew a TON of rust out. Sidebar: We did this because previous flushings with the regular T insert on the hoses were all coming out clean, due to the water hitting the blockage and finding an alternate path out of the system.

After we flushed the heater core both ways with the wand, the heat worked beautifully.


Congrats. Sounds as if this truck was not properly maintained. Antifreeze not only prevents freezing and overheating, but also has anti corrosion additives to keep the rust at bay. You may need a new radiator and heater core in the future.

Thanks for the tip, and congrats on your success. I’ll definitely put this tip in my “toolbox”.