Hello,

I am hoping someone can lead me in the right direction as I am still not sure exactly what is wrong with my heater and I want to make sure if I do this job, I am going to only do it once!

I have a 1999 F150 5.4L with 160K miles on it. I have owned many cars and trucks and the heat on this one is just mediocre at best. On a 30*F morning I can barely get the cab warm. I purchased this vehicle about 2 months ago and the last owner told me he had replaced the heater core, however at the time of the purchase i did not have enough sense to ask why. So my first thought was to check the blend door. I decided to begin to remove the dash, when I pulled the glove box and noticed most of the heater box was missing... it had been cut out, and the previous owner used duck tape to patch it back up. He used basically the whole roll, which is why I was getting a weird "flag in the wind" sound when I turned the heat on. What I did notice when I pealed the whole roll of tape away was the the heater blend door was broken, but jammed in the position that leaves the heater core fully exposed which means the limited heat I was getting should have been hot. I touched the heater core with my finger, truck on, and warm.... and it felt warm to the touch but that's not really a good indicator. I am wondering if my problem is two fold. I find it hard to believe the heater core was actually replaced because it is my understanding that whole dash would have to be removed in which case there is no reason to hack the heater box apart. What leads me to believe my problem is two fold is that I checked the coolant container today and the coolant is brown and sludgy. What's interesting is that the truck runs beautifully and never overheats or even fluctuates in temperature. It does take a long time to get warm however. I am thinking of doing a flush, replacing the thermostat, and then installing a new heater box... and additional thoughts? Any benefit to replacing the heater core again? How can I tell if its clogged? Any way to check the temperature of the core, and match it to a chart or something?

DG

 

Interesting. Sounds as if your truck has started off the same way mine did. I recently bought a 97 4.6L with 221k miles on it. Ran like a top. Not knowing how many owners there were before me, I decided to embark on swapping out all of the fluids and then doing all the preventive maintenance stuff to keep it running smooth.

My heat was mediocre at best as well. I didn't go into the dash like you did, but I tested my coolant and it, too, was a brown sludge. It didn't look good, and it tested to only one ball. I did a flush with Prestone flush, added back the coolant, even pulled the heater hoses to blow out the heater core both ways to ensure no blockages. Well, after adding everything, turns out I ended up with an air pocket causing it to overheat. The heater would come on and run HOT, which was a good thing. Eventually, though, the ugly truth revealed itself: I had a blown head gasket. I am assuming that someone had glassed the coolant or did something else for the same reason... overheat and blown gasket. Now, I am throwing a code for cyl 3 misfire, too. Joy.

Long story short, I don't have the funds to pay a mechanic to do the repair, so this just became a project truck for me... and I don't know JACK about tearing into an engine. I do, however, know how to follow detailed directions....and since a head gasket kit only costs $189 at Advance Auto... I'm willing to learn. (Yes, I know to replace the head bolts, too, for anyone else reading this.)

So, best wishes on your repair, and I know I didn't help one bit. Merry Christmas!

 

If I was in your situation, I would thoroughly flush your radiator and heater core. Try flushing the block out and take out the block plugs. After that I would take out the thermostat, fill up with a 50/50 mix of simple green and distilled water. Let it idle for like 2 hrs. Drain, and thoroughly flush with water again. Install the t stat

Fill up with 50/50 mix motorcraft gold coolant/ distilled water. You should be good then.

 

Its been my expereince when I get that runny peanut butter sludge in one of my vehicles on the lot, its a head gasket. But at the same time what the heck with the heater box?
Im thinking he had no heat, so instead of checking the coolant in the oil trick he web searched f150 no heat, which brings up this guy who sells a kit that replaces the common blend door problem. So he tried to do it himself. The kit and youtube video show how to cut the heater box open and tape the crap back together.
When what it really was is a coolant problem.
I say flush it. fill it drive it, flush again. replace thermostat, then burp it to remove the air. It that doesnt work, then it could be a head gasket. Flush kits are like $7 bux and easy.

 

It's not a head gasket, it's just that in 99 Ford used green coolant, not the gold, and after 100k miles, the green turns to exactly what you're describing.

If it were mine, I'd unhook both heater hoses at the motor and flush through each side with a garden hose until it hopefully runs clear and strong through both sides. Then do the same with the radiator, and hopefully it'll work clean as well. I'd do a new water pump and thermostat since they're both easy and cheap, and after you're all back full of green coolant drive it for a while and see if your heat works. After a month or so I'd do another flush.

That *might* keep you from replacing the heater core, at least this year, but once people let that green coolant sludge up it gets nasty and usually you have to replace the heater core and radiator.

 

The truck runs well, does not overheat, and temperatures do not fluctuate. When I did my last oil change there was NO antifreeze in the oil, and nothing on the dip stick, however I do notice periodically that the oil cap does have this sludge white stuff that forms on it from time to time, but the truck also does sit for a few days on end undriven and it has been wet here the last couple of months. Could be nothing more than moisture in the engine burning off and making its way to the cap. As I have said the rest of the engine is clean. The truck is catted so it could cover up a sweet smell but the exhaust doesn't run wet, once its warm its dry. I have had blown head gasket vehicles before and this doesn't seem like one.

On the other hand, the huge hole in the heater box is reducing the amount of air passing the heater core. I grabbed the two hoses and they are of equal temperature... warm but not hot. I am going to start with a flush and a t-stat and take it from there. Already added a gallon of flush, after a couple days of running it I will drain, flush, and refill the system and see how it runs.

DG

 

on regards to the flush, where are the flush ports located?

 

The radiator drain is on the bottom right of the radiator I think. It's a white plastic 3/4" nut looking thing. Break it loose with a wrench then loosen it till it drains, and finger tighten it, do not use a wrench. Remember to take the coolant reservoir cap off or not much will drain out.

 

I sure my heater core is plugged up too.Instead of fighting trying to disconnect the hoses ,I've gonna just cut the hoses where its easy to get to and just sleave and clamp them back together!