1988 F-150 straight 6, w/5 speed. 2wd. 119K on it. Owned it about four years and it sat for the last 12 months. Chipmunks decided to move in since I wasn't using it. Made a nice home inside the blower motor assembly for the heater. Actually chewed their way through the plastic fan. Anyhow, I evicted thier sorry @sses and put in a real metal blower fan (just in case they return).

I have very little heat, blower works fine but the temp is lukewarm. I replaced the thermostat and did the following checks with the engine running, heater on and truck warmed up: The heater inlet hose is VERY hot and the return line is quite a bit cooler, hot but not as hot as the inlet. The upper radiator hose is just barely warm. The temp gauge inside the cab hardly moves from its parked position. I'm not sure it actually works.

I put a new water pump on this a couple of years ago and replaced all the hoses at that time. Coolant never seems to go into the overflow tank, maybe it does but I never see it. Sometimes I actually get ice forming on the inside of the windows with the heat/defrost on. What should I check next? Oh one other thing, there is a flapper door in the heater box located in the engine compartment that no matter where I move the levers in the cab, it stays open. I just cut the cable and wired it so that it is always shut, since it is winter and I'm in Maine. Thanks for any ideas on what could be going on here.........

 

Could have something to do with that air mix door or one of the other doors. How did the coolant look when you changed the water pump? If it was nasty you might want to pull the return hose off the heater core then start the truck and let it get warm. It could get messy but that will tell you if coolant is making it through the heater core. I have seen vehicles with the same problem your having that have so much sludge in the heater core that the coolant hardly trickles out the heater core.

-Jon

 

>>> The upper radiator hose is just barely warm.

It should be hot. The coolant is not circulating. Could be an air lock due to a bad head gasket, meaning an engine problem. Air leaks into the cooling system, creating this air lock. I have that situation in a Chebby and changed 4 thermostats, radiator cap, until I finally realized it.

Do you see air bubbles in the coolant? Try analyzing it for exhaust.

What does the temperature gauge show? Are you running too hot? Too cold?

 

Dahammer:

I am currently having a similar problem, truck runs great, not running hot, good coolant flow through radiator but heater takes a long time to warm up and even then its just warm, never really gets hot. My truck has 300k on it, I am thinking its time to replace the heater core. Last year I back flushed my cooling system and some brown water came out, I suspect the heater core is clogging up on mine. Maybe the same for you

I am also going to replace my radiator in the next month or to, if the heater core is stopping up the radiator is probably doing the same.

 

If you aren't getting good circulation through the heater core, you may want to switch the two heater core hoses and let the fluid flow backwards through it for a few days to see if it frees it up some

 

I came across this problem with my brothers 79 f250 crew cab. Its a plow truck so the heat is a must.

The heater core was plugged. I took a blow gun and a rag and cleaned it out. I put the blow gun in the inlet side (with both hoses off) and put a rag around it to ensure pressure and let er rip. A bunch of snot came out and now it has heat.

 

That sounds simple enough, thinking about replacing it though if its not very expensive. Is the heater core easy to get to?

 

If you have A/C it should be simple if memory serves correctly.... On my 84 I had to take the glove box out remove the cover and dissconnect the hoses.

 

Thanks for the ideas........I'm thinking of just going with an new heater core...It is too cold to flush anything since all the hoses and water bibs are either frozen or shut off here in Maine..been below zero for what seems like a month..Once it warms up (like around 25 or so) I'm just gonna throw a new heater core in it. I did think of an air lock, and over the last month or so have been topping off the radiator, two shot glasses at a time, I don't think that is the reason for lack of heat, but you never know. Radiator is full now and there are no leaks at all....Temp gauge hardly moves at all...i did test the sending unit per the book and it is working..When I power flushed using a garden hose and adapter that splices into the heater hose a LOT of brown gunk came out...Put some "cleaner" in and that probably just loosened more junk up and plugged the core more...This baby is like fifteen years old and starts better than my '02 did..no smoke and just keeps on trucking...............just gotta get some warmth in the cab.

 

In both ford trucks ive owned i have had to replace the heater cores due to leaks i had a 1992 and prsently have a 1994 ford f150 xlt lariat.The heater core is pretty simple to change in theese trucks i've also changed one in a 1989 and core replacement methods are the same...........Take off the glove compartment or just unsnap it and let it hang.Behind the glove box is a black cover pop out like 6 or 8 screws and there's your heater core unhook the two hoses under the hood pop it out and bam your ready for your new core.I had the same problem recently but mine was due to the thermostat being stuck open.I've seen and also purchased a few faulty thermostats too although most are easy to spot because they just wont open at all some when they open the 1st time remain open forever!I once read when you buy a thermostat you should drop it into boiling water to insure its right before putting it in and now a days i agree with em!although discount part stores are a life saver on saving money on some parts i dont see the quality of the old family owned part stores you used to see alot. dont get me wrong i do all of my shopping at places like auto zone,Advanced auto parts, and oreilys but for the huge discounts you get you have to expect some faulty parts.But i tell you if your heat guage dont move much it sure sounds like your thermostat may be stuck open to me.Before you spend alot of time and money check it out.And if worse does come to worse and you have to replace the heater core if my memory serves me right i think they're like 29 or 39 dollars at autozone with a life time warranty.When i purchased the one for my 1992 it was a whole lot better quality than the factory one so when the one in my 1994 started leaking i just used the warranty from the 1st one i bought to get my new one for my other truck lol.Well good luck because i know how rough it is without heat i can do without an ac anyday but im not ridin or drivin without heat!


Daniel