2002 F150 V6

A week ago Saturday I drained the coolant, gently back flushed the heater core, ran a 10 minute Prestone raditor flush, flushed system with plain water and refilled coolant. This whole process where you run the engine I had the heater on an had heat.

My wife tells me on Friday that there is no heat in the truck. It's weird - when the engine is up to operating temp. and you turn it on full heat, HOT air comes out of the vents for about 5 seconds then it decreases to luke warm air and stays that way. If it was the blend door issue, why would I get hot air for the first 5 seconds? I have no idea what would cause this. (I just got the truck a little over a month ago and think it was doing it then and figured the backflush would fix it.)

Anyone know what would cause this?

thanks,

 

could just be air in the system. point the truck uphill (no need to get a severe angle or anything) pull the cap off and let it burp. while running of course.

 

air pocket in the heater is a good bet. Do as mentioned above first. I have a plastic TEE in the heater hose above the intake manifold (high point) that i can open and vent out the air to get antifreeze to refill.

 

keep eye on your temperature gage the truck in running cold causing no heat

 

Would driving the front end up on a set of ramps be enough incline?

Thanks guys for the help. I'll give that a try.

 

My 98 is weird it does not overheat in the summer however it does overheat in the winter sometimes it will in the winter and something it will not heat up. It's engine temperature driven i play around with the dial on the heater to get working right when I see it over heating I shut heater off its cools down immediately and sometimes I have do the same so the engine temp goes up for heat

 

murf, ramps would be plenty.

 

These guys are dead right when they say it can be tough to bleed the air out of cooling systems in newer vehicles. By raising the front of the vehicle you ensure the radiator/ coolant cap is the highest point of the vehicle ensuring air will work it self out . At work our Toyota forklifts are fitted with bleeder screws at the water pump to remove excess air and work great!

 

I think that did it! Thanks guys. I have heat during the test idle on ramps with cap off and off ramps with cap on. The real test will we after the wife drives it.

I wanted to check my logic on something. I was feeling the hoses going into and out of the heater core. With the heater and blower turned off I could hold my hand on the core IN for about 2 seconds until it was to hot to hold. On the core OUT I could hold my hand on it for about 10 seconds before it was to hot to hold.

Am I right in thinking even though the blower and heater were off, the heater core would still do some "radiator action" and cool the water a some?

After I turn the heater and blower on high, I could hold my hand on the core OUT as long as I wanted.

Shouldn't that indicate that the coolant is going thru the heater core and it is working?

Thanks guys. I really appreciate the help and hope this simple process fixed it.

 

Yes you are correct! The heater core acts as a "heat exchanger" just like a radiator does. It takes hot coolant and the air traveling through the heater core is warmed up. So yes the lines going into the heater core will be warmer than the ones going out. This is why if a vehicle is starting to over heat and you turn the blower motor on high and full heat you can remove a small amount of the engines heat. Years ago I bought a infared temperature gun and they work great to find the temperatures of surfaces. you can use one on your heat vents to see how hot the air coming out of the vents is

 

Wife says no heat...

I put on incline and try burp again. nothing.

I put cardboard in front of radiator and now I am starting to get heat.

Can a stuck open or closed thermostat prevent you from getting heat?

Could that be it?

Thanks,

 

what is the temp gauge doing ? How hot are the hoses to the heater and radiator top tank ? Have you narrowed down that the core is hot ? Air flow thru the heater or around it ? (blend door).

 

Sounds to me your engine is running too cold. Your thermostat opens up too quickly . Other words your thermostat might be 190 degs but it opens way before it reaches that point and is causing your engine to run too cold. If you can borrow or purchase an inferred (laser) temperature gun then you could find the temp of your top heater hose, your thermostat housing and the inlet and outlet of your heater core just to get an idea. But I'm with Steve here, where is your temp gauge even sitting ?

 

Not sure where the temp is/was setting at. I put the cardboard in before I read your message. I know that the gauge did move up, maybe a 1/4 or so because that is how I knew I should be getting heat thru the core when I "burped" it (and during the burping I did have heat) before I put the cardboard in place. I believe the heater door/blend is working. During burping between AC and heat it did change appropriately. The last time I checked, it did not feel like either heater core hose (in and out) was very hot. Neither one was so hot that I could not stand to hold them - it wasn't that way when I burped it on incline.

Now that I have the cardboard blocking radiator, wife says after awhile she is getting heat.

I guess I need to figure out where the thermostat is and if it is something I can change myself. I changed on one a chevy years ago myself. Think I had to use some kind of seal in a tube to seal it. Maybe I can find instructions (with pictures) online. Thanks

 

Well I figured out why there was no heat. Who ever changed out the thermostat before installed the new one in the wrong direction. They had the long part with the spring on it going into the housing.

I bought a new thermostat, a gasket, and yellow high tack permatex gasket sealer (like I saw on YouTube). I could not get the housing to seal. Went to a different parts store and the guy told me to use red permatex high temp RTV and no need for gasket. Waited 22 hours to let it dry before putting liquid in it. Still cannot get it to seal. I didn't want to tighten it down too tight because I heard it screws into aluminum and it is easy to strip out. So I just snugged it up. The story of my life - what should be the absolute simplest thing to do, I am unable to accomplish. So it is in a repair shop today. Hopefully they can get it to seal.

Thought I would get off cheaper doing it myself. Should have just paid to have it done. Between the permatex, gasket, and gas (11 mpg of wife driving the 02 F150 V8 4x4 supercrew for a week waiting on this repair), I'd be $ ahead.

Well at least I know why she had no heat.