I replaced the heater core about a year ago, replaced radiator about 4 months ago. I have A/C, but no heat. Fans blow high but no heat. No antifreeze smell, no antifreeze leaks. Truck runs normal operating temps.
184*

Bad thermostat?

2002 F150 4x4 4.6 automatic 170+K miles

 

No, the thermostat if bad, will only make the truck run hotter. If you are running at normal, temp, it has to be a blockage some way, keeping the hot water from flowing through the heater core, or the blend door for the air is not openning.

 

Well, a thermostat can get stuck open, but then it shouldn't reach operating temperature. What thermostat did you put in it? Something like a 160 degree is not going to put out real hot air. If you put in the correct 195*, you should be seeing higher operating temperatures than 184 degrees. It might be time for a radiator flush. If the hoses to the heater core or the core itself is blocked by corrosion, you're just not going to get much heat from the core. Try touching the heater hoses to and from the core and see if they seem to be the same temperature to rule out a blocked core. But if the blend door isn't working that will also prevent air from the heater being directed into the cab.

 

Yes, my comment was based on the fact that it was running normal temp, so unless the 184 was reached after quite a few miles, it could not be stuck open, and even if it was open, once it reached that temp, you should feel some heat.

 

Agreed. I was just giving him a few more options. I used to run a 180 degree thermostat in my old bronco and never gave me as much heat as switching back to a 195. But that was a lot of cab to heat up.

 

I started to make the comment, I am not sure about the 4.6, but I know the 5.4 needs to be at 195 or even a little warmer for efficiency. I would consider replacing it with a 195.

 

I've never replaced the thermostat on this particular truck. Bought it with
93k on the clock, so I've put 80k on the same stat. That 184* temp has been normal in the cooler weather, after about 25 miles of driving. During the Texas summer, it would average 198* or so, but never more than 202* even with the AC on in traffic. So the thermostat is still reading steady from what it has always been.
I thought about the blender door, looked at the "Heater Treater" fix. Any other way to tell if the blend door is faulty? My control **** seems fine, there is some consistent slight pressure when going back and forth between blue to red. I would think a busted blender hinge door would result in no pressure at all? I was thinking about chopping out the glove box and plenum as they suyggested to take a look, but I wanted to be sure what it was before I started chopping away. Especially if it is the heater core AGAIN, and I have to pull the dash apart AGAIN...
Any other ideas on how to check for sure?
Oh, and I don't have steam blowing out the vents either if nyone was wondering...
Couldn't be water pump...
Guess I'll start by checking the hoses at the firewall... and go from there...
Thanks for the ideas, I'll keep you posted

 

If you ran that warm, then you probably have a 195 in it and the 184 is due to cold weather. Yes, check the flow of coolant in the heater hoses first. See if it is circulating thru the core.

 

Well took the truck for a spin, got up to normal 185* for 44* weather, and checked the hoses going into the firewall. The one from the intake is too hot too touch for long, and the other (return line I guess) isn't quite as hot, about hand warmer hot.

I am getting a smidge of heat out of the vents (I originally said none). On blue cold it's about 44*, on red hot it MAY be 65*.

What's next?

 

Sounds like the heater core is plugged up with dirt or corrosion. Get a chemical flush and flush out the whole cooling system. If that doesn't open up the heater core, I think you'll have to change it.

 

This sure sounds like the blend door to me, But that return heater hose should be close to the same temp. You might try flushing the core both directions with a garden hose.

 

do you hear a difference when switching the blend from cool to warm? usually u can hear a change in air flow sound. kinda hard to describe...

 

I did notice something strange last night on the way home. When I have the cruise set and I hit a down hill, or when I let off the accelerator, the air becomes stronger out of the vents (not hotter, just blows harder), ususally staying consistent for about 18 to 20 seconds. Then if I got back into the gas, it would disappear again, no air out of the vents what-so-ever, this would last until once again I took my foot off the throttle.?
Turning the air control from blue to red, I don't "hear" anything, like the blender door opening and shutting. I even pulled the glovebox out just in case maybe I could hear a little better, but still nothing. I figured I should hear a "thwump" sound when the door open and closed.
I don't know, I'm gonna flush the system, then try the blender door since it's second easiest. If that's not it, guess I'll rip into the dash and get another darn heater core.
Thanks for the ideas. Will keep posted.

 

You might try this because it sounds like your door is moving when your not telling it to.
First turn blower off.
Find a step hill going up ward and hit the brakes while turning left, this would swing the door over not covering the heat core.
now turn blower on, defrost works the best.

This test only works if the door axle plastic tabs are broken completly. If the tabs are not broken completly you could remove the stepper motor and turn the door manualy . See heater treater video1. On are f150 small plastic pieces fell out on the carpet when we pulled the moter. Pulling all the stuff from under the dash only took about a 1/2 hour, plus you can still drive around with it this way.

 

Well, pulled the glovebox out this morning and cut into the heater core box via "heater treater" instructions. I just bought the new dremel tool that has the high speed vibration blade, worked ouyt really well for this, all the cuts were perfectly straight and easy to do, and didn;t even leave a bad mess. Anyway, got inside and the blender door is working fine with the turn of the ****. so there goes that theory.

I'm gonna do a heater core flush once I get the feeling back in my fingertips..
i hope that works.
Geez I hate to pull this dash apart again, and it's only been a year since I installed the last heater core... But, what-do-you-do?

Wish me luck guys...