1997 Foor F-150 heat problem 4.6cu.

[x1957x]

I have been struggling with this for awhile now. Here is what is happening, it gets half way warm at idle ON--panel(on the control switch) but cools down when put on defrost. I Put in new door on heater core and new control switch and a new thermostat but still does the same. Should say that it gets to operating temp but the bottom radiator hose DOES remain cold though.Seems that as I rev it up to about or over 2200rpm's it seems to heat up a bit. Can get a little warm when ideling but when I get it on the highway for awhile it gets cold then.. Thanks to all!! Could it be bad impeller on the water pump?

[Jeremy airjer W]

The temp gauge gets cold or the heat coming into the vehicle gets cold?

To me it sounds like you maybe have two issues. The thermostat you installed is wrong or defective and/or your heater core is plugged.

I should add make sure the coolant level is full and make sure there is no air in the system!

[Walleyehooker]

Your thermostat could possibly be stuck open. I would test or replace that first as it would be the easiest and cheapest.

[Scott K]

I hate to say it, but on t-stats, go OE. Way to many problems with aftermarket t-stats.

[JOHNBIGDOG]

I have been struggling with this for awhile now. Here is what is happening, it gets half way warm at idle ON--panel(on the control switch) but cools down when put on defrost.

So are you talking the temperature of the outlet air correct?

I Put in new door on heater core and new control switch and a new thermostat but still does the same.

Its a shame you didn't replace the core, it may be plugged. (my opinion) or may be a blend door actuator, but its odd that you state it seems to get cooler when you put it on derost.

Should say that it gets to operating temp but the bottom radiator hose DOES remain cold though.

You should be more concerned that the upper radiator hose is getting hot when the T-stat opens. heat rises, cold falls. Also one of the heater core hoses should be hot, the other cool. This is what should be happening in a correctly operating core, as the core pulls heat out of the coolant the coolant cools down in temp. Also should mention that there should be a restriction "deal" in one of the hoses, it is very noticeable as it has a clamp on the outside of the hose holding it in place. If this is missing it may be a possibility that the coolant is going through the core to fast and the core is not able to pull the heat out of the coolant properly.

Seems that as I rev it up to about or over 2200rpm's it seems to heat up a bit. Can get a little warm when idling but when I get it on the highway for awhile it gets cold then..

The truck or the temperature out of the heater? I'm going to assume your talking outlet temperature of the heater core?

Thanks to all!! Could it be bad impeller on the water pump?

Well my next question is what does you coolant look like, have you flushed it recently? It may be worth a shot to hook up a garden hose to the heater core ant try back flushing the heater core to see if its full of mud from lack of maintenance. One could remove the serpentine belt and try and move the pump pulley, if it has play in it, it wouldn't hurt to replace it. I haven't seen the impellers go bad in these trucks, but I'm pretty green, and we don't see too many of these "old" trucks at the dealer much.

on a side note if there is allot of air in the system, bad head gasket, it may cause similar issues.

[x1957x]

coolant looks to be o.k..how do you check to see if there is air in it? The air that comes out of the defrost into the cab gets cold when you put it on. And the bottom heater core hose is a bit cooler than the top. Why does the bottom of the radiator hose stay cold? I guess if the thermostat isnt closing (or installed wrong?)it will stay cold right? And if it was the heater core that was plugged why does the hose stay cold?

[x1957x]

Dont get me wrong JONBIGDOG. It isnt red hot by all means when on the panel. Just cools down considerably when put on defrost??? Its odd to me to why this happens!! When I changed the blend door I dremmeled out a hole in the heater core area via a Video on you-tube. Have to watch it. Saves alot of time and money of course. Thats why I didnt change the core. Its odd the bottom hose on the heater core does get slightly cooler. IF it was I a head gasket I would have to say that there would be some coolant loss. Thanks again. On a further note I still need some help with this!Also I have flushed the radiator to.

[Jeremy airjer W]

This is what we need to know before you do anything.

What is te coolant temp sensor reading for temperature. You will need a scan tool to find this out. It the temp never gets to at least 190 degrees than you have a thermostat issue. If the coolant temp drops while you are driving, you have a thermostat issue. If the temp gets up to 190 and holds steady while driving than we don't need to worry about the stat or pump and can concentrate on the HVAC side.

[Scott K]

If the engine coolant isnt getting to the correct temp, and when you have it on defrost, the ac compressor kicks on, making the little bit of heat you have, cooler. So if it isnt up to where it is suppose to be, you will notice a temperature drop.

I am pretty sure you have a bad t-stat, or a plugged heater core.

[Jeremy airjer W]

I would have to agree with the above.

[x1957x]

Is that why the bottom radiator hose is always cold? Wouldnt it still get hot if the core was plugged. Has to be the thermostat then. My wife made a comment about this. She thought we started having problems a year or so after we installed a remote start. (Can that have anything to do with it?) I do know that the resovoir(anti freeze) does not get overly warm to.. Full of anti freeze also. So I can elimanate that. I know that it gets warm--(not hot)-- when at an idle. But if I drive it down the highway for awhile it does cool down a bit even on panel. The hose that comes out of the core is hot and the other one isnt hot but (maybe) a very warm. Thanks again.

[Scott K]

I would get an OE t-stat, and put that in it. They are easy enough to do, and you wont have to drain the entire system.

[fishing tech]

Hard to diagnose without actually seeing what is completely going on. If the stat doesn't take care of it the impellor on the water pump may be loose or rotted away. Could be as simple as an air pocket in the system or as bad as a blend door.

[x1957x]

I have questioned that impeller earlier on and as far as the blend door it has been changed already. why does the bottom radiator hose not get hot LIKE IT SHOULD if every thing was working properly. I am going to try a OEM thermostat and see if that makes a differance. I know that the top heater hose gets really hot and the bottom a good hot! I really am not leaning toward a heater core being plugged though.. let me know and I will post the findings after I put in the new OEM stat!!

[Jeremy airjer W]

If its cold outside the lower hose may never get hot with or without a properly working thermostat. Heat rises. Hot coolant comes out of the engine via the upper hose, it then enters the radiator where the heat transfer takes place. The coolant exits the radiator after being cooled through the lower hose.

Like I said if its cold enough outside the lower hose may never get hot. If the thermostat is stuck open the lower hose may never get hot. If the thermostat is stuck open the upper hose may feel warm but may not feel as hot as it should.

One last thing you could try is start it up cold and just let the engine idle. If you feel the upper hose getting warm before the temp gauge gets to the half way mark than the thermostat is stuck open. The upper hose should not get warm/hot until the thermostat opens.

I am not on board with the impeller theory at this point. It would be overheating especially at higher speeds if it where not pumping enough coolant through the engine.

[fishing tech]

If your heater hose (upper) and the lower is hot and you have no heat the core has an air pocket in it, is partially plugged, or you have a plenum problem. By hot can you hold our hand on the hose and how long? After working on car for 30+ years I can hold a hot heater hose for maybe a minute. Lots of calyces. Most friends get about 10 seconds or less. Hot going in and coming out is good. But your hot and the hot you need to get heat maybe different.

To get the air out after you replace the stat, Fill with antifreeze, leave the reservoir low. run the engine and hold the upper radiator hose. watch the reservoir, if the coolant gets below the bottom add. Once the t stat opens the upper hose will get real hot. Hold the throttle or have someone step on the gas pedal and hold the rpm at 1500-1800. add coolant to the reservoir to the full mark. install the cap road test it. let it cool down and recheck the coolant level. if it is low, the reservoir should not be empty top it off and you should be good.

I hope this helps and it fixes your problem.

[x1957x]

Thanks alot and this weekend I will work on it. Thanks 4 wanderingeyes for the stat info which is the first thing I will do. 2nd, thanks Jeremy airjer W for the way to check the t-stat. I will do it and let you know. 3rd, thanks fishing tech, JONBIGDOG and WALLEYEHOOKER. I will let you guys know the outcome!

[delcecchi]

Just take a picture or make a note so you don't put the new one in backwards. Makes it overheat. At least it did my barracuda on my wedding day.

[Jeremy airjer W]

Spring side always towards the engine!

[delcecchi]

Spring side always towards the engine!

Now you tell me. Too bad I didn't know that in 1970

[JOHNBIGDOG]

Now you tell me. Too bad I didn't know that in 1970

That man wasn't even born yet, I know for a fact. Unless his mother lied to me.

[Jeremy airjer W]

That would be correct.

[delcecchi]

Still would have been nice to know. I had a 50-50 chance of getting it right. Made it to within about 3 or 4 blocks of the church before the needle was almost pegged. It was only about 90 that day.

[Jeremy airjer W]

A a general rule I don't work on anything built prior to 9/1971.

[fishing tech]

A a general rule I don't work on anything built prior to 9/1971.

That's the easy stuff, well might be a little rusty in this climate. I would love to go back to pre 80's. Less electrical and emissions. More wide open. But the new stuff keeps you guessing. (what will they come out with next)