1996 4.0 OHV - No heat, will soon replace thermostat, have questions... | Page 2 | Ford Explorer Forums - Serious Explorations

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1996 4.0 OHV - No heat, will soon replace thermostat, have questions...

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your factory coolant temp gauge is not a good place to read actual temp
It is good for letting you know if you are about to overheat
The gauges do wear out in time and can need repair, the sensor you have installed may not produce the same signal, as factory the signal may have degraded over time....there are many reasons why the factory gauge maybe stuck on cool

But as a mechanic you must move past that
We need to find out why you have no heat
with the eatc the first thing to do is run self test check and clear any codes
the next thing to do is start checking actual temperatures in your system, we can use a real coolant gauge for this, we can use a scanner and read what the pcm is seeing for coolant temp in real time, we can use an infared thermometer and physically check the surface temps in the cooling system at different time (both sides of the thermo housing, upper and lower radiator hoses at the radiator, heater hoses going into the heater core, etc etc

if you do not have a mechanical, coolant gauge or an infared thermo then the simplest test is to see of both hoses are hot/warm to the touch when the engine is at temp going into your heater core

heater core maybe blocked
Heater control valve may or may not be opening (Vacuum from eatc in dash controls this)

I know you are stuck on the system over cooling, we are moving past that, at least for now.
Having many of these trucks over the years, some will read to the left side of 'NORMAL" in the coolant gauge and some will read in the middle, other trucks lean to the right. Ford will tell you that everything in that gauge that is pointed at letters in the word "NORMAL", the engine is in its proper operating range. A mechanical coolant gauge is a much better choice if you are questioning your factory gauge. I have one in the shop I use just for diagnosing engines, we remove the factory sender, install mechanical sender and now we can see what is actually going on with the cooling stack, fac, fan clutch, waterpump and thermostat.........all of which you have recently serviced or re done in an effort to stop this overcooling and restore your heat. So we are saying, for a minute forget the factory gauge and do some real world diagnosis

a mechanical coolant temp gauge hooked up to the lower intake should show water temps slowly rise with engine at idle. Bring engine to 2200 rpm steady for 1-2 minutes and operating temp will be reached fairly quickly. Operating tempos for these rigs are 198 degree thermostant factory, this means the water in the engine will warm up until it reaches 195 or so temp behind the thermostat. The thermostat should be fully open by 198 degrees.... allowing the heated water to travel through and into the radiator / cooling stack to be cooled by the fan.
The gauge should read something like this..... warm up from cold to around 195-205 degrees then you should see a quick drop...down to 185-190 and things should steady out around 195-210. The spike you see is the thermostat opening. While driving the "normal' operating range of these engines is 195-215 degrees
you see 220 its okay but running hot (summer, high load, high demand, stop and go, etc etc)
230 i start to suspect issues
240 time to pull over

heater core hoses = hot to the touch or not?

Good news, at least I think... Heater core hoses are BOTH warm. Ran car for 15 minutes with heat off to warm engine, then turned on the heater and let run another 10 minutes before checking the hoses. So, after 25 total minutes of running, the lines were... warm - not hot, just warm. Both were the same warm temp though, so I assume that means the heater core is totally fine, and the issue is something else.

Secondly, I did the EATC test, twice. Once before I ran it (engine cold), then after 25 minutes (engine warm). BOTH times the display was 888 so apparently there is no issue with the actuator, but could it possibly be the door itself is broken in a way that wouldn't give an error code?

My dad has an OBDII scan tool, not sure if it will display temp, though. I will ask him about it. I know it will work for Fords 96 and up for codes though. (Although the Explorer is not showing a CEL right now).

It will show pcm coolant temp on the scanner

So with both hoses warm we assume the heater core is not plugged and the heater control valve is working!

Now time to move onto the blend door itself
You will need to remove the blend door actuator from behind your glove box and have a look at it.
There are 3 screws to remove they can be a real pita but do able with the correct tools
With the actuator removed but still plugged in you can watch it turn as you command hot to cold to hot etc
Then look down in the hole with a mirror or your cellphone camera and see if the bled door axle is broken/ split/ Mia

Well, I guess the majority of the problem was being caused by incomplete burping of the system. I previously went through the afternoon long procedure of adding, burping, adding, burping, for 3 hours... and I thought I had all the air out. Alas, I didn't. So I added more coolant and am going to continually keep an eye on the level, waiting about an hour after driving it to let it cool and then open the radiator cap to see, and fill more if needed. As it seems, I think most of the air has burped. That being said... The heater is only blowing lukewarm now. It's better than it was, but not where it should be. I checked everything I knew to check. The blend door is working (opens/closes when switching). And, using a laser temperature-gun thermometer, I have found an interesting discrepancy - While the engine is ON but the heater is OFF, the temperature on the thermostat housing is 180, the temperature at the base of the oil filter is 190, and both heater core lines are 130. Seemingly that is darn near where it is supposed to be (and is further confirmed by the fact that when you shut the engine OFF, the temperature at the thermostat housing rises to 205). And I would say such temperature readings basically confirm the engine is NOT running too cold as I had previously assumed (which means the dummy gauge is horribly inaccurate). However, as soon as you turn the heater ON, all 3 locations' temperature readings drop by 10 to 15 degrees: the thermostat housing drops to between 165 and 170, the base of the oil filter drops to 180, and the heater lines drop to 120. Now, maybe that is supposed to happen, considering turning the heater on means the coolant's heat is being used/utilized to heat the cabin, and that drop can also be attributed to the thermostat opening. But I'm not sure.

So... are these temperatures where they are supposed to be, or is it still 10 or 15 degrees below what it should be? And, knowing the heater core isn't clogged, knowing the blend door is indeed switching positions when switching from A/C to heat, and knowing the heater core lines are at 120 to 130, what could be the reason that the heater is only blowing lukewarm? This car used to blow super hot air out of the heater, so I know something still isn't right. And I also want to ask, what position should the door be when the heat is on, and what position should it be when the A/C is on? I mean, I doubt it is backwards, but I reckon I may as well be sure.

EDIT: Just found this: Coolent Temp Sensor Location
Could the issue be the sender? If the sensor only tells the gauge what temp to display, but the sender has input/output data with the computer, maybe that could be a problem?

Sender sends variable ground to gauge only. Sensor sends to pcm

Again, if you get truck parked uphill, or on a ramp, engine running with HVAC set in floor hot, the air will rise to radiator cap
Goal is radiator cap higher than heater core inlet.

Your fan clutch maybe stuck causing the fan to run all the time which is keeping the temps down low. You should have a 195-198 degree thermostat in there it kinda sounds like you have a 180 installed

Good work this far!
These systems can be a pita to get all the air out of.
Parking on a hill or run it with the front up on jack stands is the best way to release the air trapped behind the thermostat. I have also poured a coffee pot of hot water down the upper road hose before to get the thermo to open and release the air, that truck was being very stubborn

I checked the thermostat before installing it. 198F was on it, so unless MotoRad put the wrong number on it, it should be correct.



It looked very well built when I inspected it before installing it. And yes I made sure to place it in with that little relief valve on the top, I just flipped this image so you could read the temp. I will probably use the hill technique this weekend to see if I can get any remaining air out.

when you shut the engine OFF, the temperature at the thermostat housing rises to 205

Wouldn't this ^ indicate it is indeed a 198F thermostat? I mean, at the same time, I see your point, though, as the laser temp-gun is showing 180F when pointed at the thermostat housing while the engine is running and has been running for half an hour. Whenever I get around to doing the hill technique, I will watch the fan the whole time to see if it is continually running.

Well, I did the hill trick, front end was probably about 20 to 24 inches higher than the rear end, and it burped more than it did before. It helped somewhat, however, it would seem as though the fan is indeed stuck on. Cold start, fan turned on immediately, ran it for an hour, never stopped turning. Is it something that can be fixed, or is it a part in need of replacement?

Well the fan will always turn but it is mounted to a clutc
The fan clutch has a spring in it that reacts to under hood temps, as it gets hit the clutch engages and the fan no longer freewheels instead it is forced to move a ton of air when the clutch “locks up”
These do wear out, one this old is suspect

On these rigs I can tell if a fan clutch it worn because it will sound like a b52 at all times, not just when hot.

When you installed the thermostat you put the spring towards the engine correct?

It’s a simple thing but have to ask

There are YouTube videos that show how to properly check your fan and clutch

Ah, okay, yeah it probably isn't the fan clutch causing any issues. Definitely doesn't sound super loud. I just wasn't sure if it was supposed to be on all the time. It's pretty quiet at the low speed, so I'm glad to be able to check that off the list of possible issues.

Yes, spring side forward towards the engine; relief valve on top.

I am wondering if maybe the heater core isn't completely clogged, but just partially, possibly at a reduced flow rate of about 1/3 to 1/2 of what it is supposed to be. Should the heater core hose lines be that much lower in temperature than that of the thermostat housing (a difference of 50 degrees)? Also, knowing that when I turn the heater on, the thermostat housing drops by 10 degrees to 170, and the heater core hose lines drop 10 degrees to 120, that seemingly suggests the coolant is flowing through the heater core (as the loss of heat indicates the core acting as a radiator). But I don't know how much difference in temperature there is supposed to be when comparing the thermostat housing to the heater core hoses.

As an aside, if the coolant temp sender is only for displaying the temp on the gauges, but the sensor sends data to the PCM, could there be any issue with the sensor, or am I conflating two unrelated issues? What does the PCM do with the data sent by the coolant temp sensor (i.e. how does that affect how the engine runs, and could that be causing the engine to run slightly below the temperature where it needs to be via a slightly rich air-fuel ratio, or is the task of air-fuel ratio handled only by O2, MAF, and MAP sensors?)

Good line of thinking

I would back flush the heater core
We use air and water

The coolant has always flowed one direction into your heater core. By reversing it… well you wouldn’t believe the crap that will come out of there

Also remove
Blower fan make sure no leaves built up in hvac box
Same thing for the cowl drains under your fender skirts the cowl must be able to drain if you can get a bunch of debris in there stopping the fresh air intake and causing debris to clog the hvac system

The pcm uses info from the ect (engine coolant temp) gauge to switch fuel trims as the engine e warms up

I don’t think it is causing issues, having 205 degrees at back of the thermostat is proper

FINALLY! I fixed it. Did the flush on the heater core. Went to Ace and bought a brass 5/8" hose adapter, and some clear 5/8" flex tube, worked like a charm. I flushed it 6 times, meaning reverse flow once, normal flow once, repeated twice. All the nasty crud came out (ran it out into a bucket and dumped it out in gravel where the cats couldn't get to it). Hooked it back up, let the engine run about 25 minutes, turned the heater on and it was HOT! Used the temperature-gun again and the thermostat housing was once again 180 while the engine was running, and 205 when you turned off the engine. So that's where it should be. The stupid dummy gauge's erratic up and down behavior doesn't correlate with the readings from the temp-gun so I'm just either going to ignore the gauge or possibly eventually change the coolant temp sender and sensor. I don't really care enough about it right now so, as long as the heater keeps pumping hot air like it is, I'm done👌

Thanks for the help everyone.


The factory gauge is not the greatest lol

You did it! Backflush the heater core is the way to go
Glad it worked because changing the heater core requires removing the dash yikes


I flush my heater core when I change my coolant (every 60k or so). I use the same setup you do—the garden hose barb adapter and some clear hose to connect to the heater core. Flush both directions.

It’s great preventative maintenance

Awesome, and glad you thought of your neighborhood cats...just for anyone reading this they are DRAWN to the sweet smell of coolant and it will KILL them if they slurp even a little. P.S. The more people I meet the more I like my cat.
"Effects of Antifreeze on Dogs and Cats: Only a teaspoon or two will poison a cat, while three tablespoons will poison a 15-pound dog."