Succesfully changed thermostat & waterpump & coolant,ran system as I filled it,All seemed well yet drivng down the road in 2-3miles NO HeeT! Cold air .Spent all day today flushing the heater core & replaced coolant & again, slightly warm, then &cool as air-conditioning, then slightly warm then cool again.I understand about airlocks yet this has me baffled.Was working well up to the cold snap & then all these cooling repairs.& its mal'fing.( cab heater).
When looking at my coolant circulation i see the line to the water pump is the return to engine & the one that is cold to touch.The one from the block is hot like a soupkettle. i was able to blow through the heater core with little or no effort & a garden hose ran freely.
Am I correct in the thought that this flow from engine to heater core & return is a siphon feed & under little pressure from the water pump??
Is it a heater core that I'm ignoring & hoping to solve with all these other fixes even though they were do?
Anyone kno about the flow directions .Its is a '92 F250 with a 7.3 i.d i. Engine temp is normal.
Thanx for any & all help!!

 

Well it seems like youve covered most everything.How do the heater hoses look and feel.I dont suppose you have one colapsed inside,cutting off the flow.Might be worth checking.

 

I am ttrying to remember my heater lines on my 88 which should be the same. It came from the head (hot) to the heater box valve. Went thru the heater and returned to the water pump. Get someone to help you. Let them work the heater control in the dash and you go under thehood and watch the valve working. After they have moved the lever all the way to hot, see if you can manually move the switch a little more. If the valve doesnt move any more, try unhooking the return hose from the water pump and see if you are getting return water. Good luck and dont get tangled up in moving parts. Bill

 

Biulde12
good answer on the moving parts,
my nickname is fyngrz & I have all ten after 30 yrs of wrenching & ripping.
now about this " called a valve , in my'92 I do not see a valve yet there is some vacuum lines on the side of the heater box.In feeling my hose & checking flow there has been some improvement Today.
It has been building up pressure with the cap on tight, top hose sweels then after a30 min drive I release all that pressure & a bit of glycol. Do these systems work under a pressure or is this air locks working their way up &out?? Hope so!!
I had a garden hose running trough the core& hoses are fresh.Me thinks I'm do for a core?Hope the weather breaks to above freezing.Thanx for your points.
Wayne

 

I am wondering if you have the hoses reversed on the heater core. If you can run water through it and it is not leaking....I am not sure about the hoses routing being the same as my 86, but I do know if reversed it does not work right.

 

I am almost 100% positive that there is no wrong way to hook up the hoses to the heater core. Will work either way. Sounds like your problem might be with one of your flapper doors under your dash not opening or shutting when you turn your control to heat. You could be getting hot water through your heater core but be pulling cold air from your fan through the evaporator core to your floor. You can check the door by pulling the cover off of the heater core and put some vacuum on the actuator to move the door. At least it is this way on my 86. Also, if your door is cable operated, your cable may have broke that switches the doors. Do you have some sort of heater valve in one of your heater hoses? If so, by-pass it and see if you get heat. It may be plugged or malfunctioning.

 

Im going to chime in with Horton-racing. I only had one vehicle ( besides my truck now) that had heat. I tried all those things that most people try,thermostat, flushing, heater core, but I never ripped open the dash and went to the flaps. Now, my truck had great heat and one day a, click, and it was gone. Once again I embarked on the frustrating journey of "what the heck could this be" why am I not getting heat. So I decided to do a lot of research before doing anything at all. Heres what I found. If your system is airlocked take out your thermostat , force it open with your thumbs and stick two aspirin under that little tab to lock it open. Then fill up the big hose and everywhere else that you can manually before you start running the engine and filling the rest. That is supposed to allow the coolant to run free for awhile and get to where its supposed to go and the aspirin will dissolve and not hurt anything. Feel your heater core hoses if both are hot then its not clogged. If you flush your core, flush it backwards and forwards so you dont lodge anything in there. After all the info I aquired I was left scratching my head. So out of anger I pulled my glove box out got to the heater core stuck my hand in the channel and started moving the stat control and found my flap opening and closing. Now I was mad. I didnt know how much it was supposed to move. So I turned the vent on and found another flap moving and it moved ALL THE WAY 180 degrees. So I went back to the stat control and realized that in order for there to be heat those channels must be sealed, but I didnt know why it wasnt. I said "screw Ill break it and leave it on all the time" when I grabbed the flap and yanked on it I heard a couple of cricks but realized that it wanted to move. So I started feeling the edge from top to bottom and found that a pen fell from the defrost vents and made its way down there. Ipulled it out turned the dial and Wala.......... HEAT....and now Im phsyched because that was free and put some new light on the no heat subject from my other vehicles. Happy Diagnosing and God Bless
P.S. I felt tension in the dial when it was all the way up on hot. Like it wanted to spring back. Go with your instincts I should because I thought it was the flaps right when it happened two years ago.

 

Well Now F- friends
I see that i am not the only one that has had this bad dream Yet my heater has come back to warmimg the cab & the hoses are hot(feed) & warm(return) . burped my rad & squeezed my hoses & drove the snot out her for 2 days. I still may have foriegn objecvts doewn the vents but its "heatin the beast up enough that i can take the gloves off !!
I will look in to a fresh core a.s.a.p.
& post the results when done
-30-35 wind chill is tough to beat but shes(truck) better than earlier this week.Thanx for your stories of experience that is what trades secrets are about.

 

Wayne,
I've been working on an '84 and do not know the difference in the truck heaters. I have been to the local "recycler" several times to get parts of my heater. I had to replace one vacuum motor and the vacuum hose that connects down by the heater core and goes to the vacuum valve (switch). It had something plugging it. I finally took my air hose and blew thru both ends before whatever it was dislodged. Anyways, in all the trucks I took parts from there were "items, (pens, shotgun shells, etc.) in the housing just to the left of the heater core. And they will prevent the temperature blend door from opening. Pretty easy to get to.

Also, as mentioned, if the cable going to the temperature blend door that controls the heat isn't working correctly cold air can come in past the heater core and never gets heated. That's how you get vent air in summer.

 

We have the same problem on our truck (sig). I'm going to look at the flaps and control cable first. Am I correct in understanding that this is accessible from the dash? Do I have to remove the whole dash or is there a panel somewhere? Thanks for your help.

 

Ben,
I can't inform you about your year. On an '84 there are about 6ea 5/16" screws to remove, but to get to them you need to remove the glove box liner. Just look under the glove box area and see if there's a cover over the heater core you can get to!

 

I'll try that this weekend, Thanks alot!