Heat not working - Temp gauge all over the place

[Zachj83]

So... 1993 Ford Explorer, 94K miles, original everything (as far as I can tell). It takes quite a while to reach normal operating temp (almost 5 minutes, sometimes more), and then when it does, the gauge jumps back and forth from the "N" and "L" in normal. It is never stable on the gauge; it's always moving. Also, the heat does not work. The fan blows good air, however the air coming out of it is about the same temperature as the outside air.

Things I've tried:
Coolant flush
Replaced thermostat (twice)
Checked radiator, reservoir, and hoses for leaks/air bubbles

Also, the hoses both TO and FROM the heater core in the firewall do not get hot to the touch. They get warm-ish. The upper and lower hoses for the radiator are also about the same. They get hot... but not as hot as they should. It's almost as if the engine isn't getting hot enough. But that doesn't make a whole lot of sense. Any help would be appreciated. Thanks!

 

[gmbroy]

have you checked to see if water flows through the heater core ?? are you positive the thermostat is installed the right way ??? spring to the engine . are you running the 195 thermostat . just a few ideas you can think on . keep us posted .

 

[gmanpaint]

The coolant might not be making it to the heater core, if that valve right at the firewall is not working. I had to replace a couple of them on the Explorers over the years.

You replaced the T-stat, but did you Burp the engine to remove all the air? This will help you if you didn't. There is a certain method to do this correctly, but basically, you want the radiator a lot higher then the rear end when you do this. A floor jack helps if you can't find a decent hill. Twist rad cap one click to loosen, start the engine, turn fan on high, set to vents or floor, set temp all the way to warmest. Let run for at least 10-20 mins. Watch for coolant boil over a little is fine, as the air releasing will take a little with it. A lot of constant coolant loss, and shut it down. This would be from a different issue, such as a water pump, T-stat, etc...

 

[Number4]

Buy a coolant evac and fill kit, only real way to put coolant in a system and remove all the air.

Something like a FJC 43610

Search around for different models or sales. I paid $50 something. It's come on handy.

 

[gmbroy]

That is interesting . I have never had to do that on a first gen explorer . I have a friend with a new Nissan truck & it took a couple times of this method to get it right . I burp mine & it fills correctly all the time . BUT strange things happen . LOL Keep us informed of your progress . it helps us all learn .

 

[Number4]

@gmbroy , once you have the tool, you use it on everything.

 

[Zachj83]

@gmbroy - Yes, the heater core is getting water. The thermostat went in the right way (I had to double check the first time after buttoning it all up), and I have a FailSafe 198 deg. thermostat from Autozone.
@gmanpaint - Thank you for the tip on how to burp the air out of the engine. Once I have a day off (tomorrow) I will try it and see what happens. I'll update this thread with my results.
@Number4 - Thanks for posting that video. That's extremely helpful. I'll try and locate one here locally to pickup and use. If not, I'll have to use the burping method suggested by @gmanpaint.

Thank you everyone for your time and help. I will update this thread in the next couple of days with any results I may have.

 

[natenkiki2004]

Just to throw this out there; I installed a coolant filter setup on my Explorer (you can find it in my signature) and in that setup I put 90 degree valves in it so I could shut off the heater core in case it leaked or during the summer. It was one of those "why not" things. A couple months later I checked the fluids out because I was going to haul a large double-axle trailer. One of the things I had gotten in the habit of doing every so often was cycling the valves closed then open again because they seemed to stick. Anyway, I barely get down the road and my temp starts climbing higher than normal so I watch it and it goes back down. I get on the highway and it climbs again but comes back down once it reaches a certain point. I get to my destination with the trailer without problem.

Long story short, it wasn't long after that trip that I realized I had shut off the suction side of the heater core and forgotten to re-open the valve. Once I did that, the temperature stabilized and all has been well since (over a year).

I'm SURE your fluctuating temp gauge is due to no flow through the heater core. You gotta figure out why.

 

[Zachj83]

Just to throw this out there; I installed a coolant filter setup on my Explorer (you can find it in my signature) and in that setup I put 90 degree valves in it so I could shut off the heater core in case it leaked or during the summer. It was one of those "why not" things. A couple months later I checked the fluids out because I was going to haul a large double-axle trailer. One of the things I had gotten in the habit of doing every so often was cycling the valves closed then open again because they seemed to stick. Anyway, I barely get down the road and my temp starts climbing higher than normal so I watch it and it goes back down. I get on the highway and it climbs again but comes back down once it reaches a certain point. I get to my destination with the trailer without problem.

Long story short, it wasn't long after that trip that I realized I had shut off the suction side of the heater core and forgotten to re-open the valve. Once I did that, the temperature stabilized and all has been well since (over a year).

I'm SURE your fluctuating temp gauge is due to no flow through the heater core. You gotta figure out why.

Thank you so much Nate. It now makes sense to me that the temp gauge fluctuations and the no heat problems are intertwined. Any suggestions as to where to begin to figure out why I've got no flow through the heater core?

 

[gmbroy]

@gmbroy , once you have the tool, you use it on everything.

I am going to get one of these tools as you have to have one . all the new systems require them . Thanks Number4 I can see how it will work on all systems & once you use it you will use it on everything .

 

[gmanpaint]

That tool wouldn't work on either of my Fords. The overflow bottles are not sealed tight. Would that vac tool fit into the radiator neck and tighten? Just plug the overflow hose to get it to work?

 

[natenkiki2004]

Thank you so much Nate. It now makes sense to me that the temp gauge fluctuations and the no heat problems are intertwined. Any suggestions as to where to begin to figure out why I've got no flow through the heater core?

Being a 1993, does it have the heater control valve? I might suspect that or the vacuum line going to that.

 

[Number4]

That tool wouldn't work on either of my Fords. The overflow bottles are not sealed tight. Would that vac tool fit into the radiator neck and tighten? Just plug the overflow hose to get it to work?

It works via the radiator as well. Via the radiator, it plugs the hole going to the overflow. I used it on my '94.

 

[Zachj83]

Being a 1993, does it have the heater control valve? I might suspect that or the vacuum line going to that.

Based on everything I've read and seen, there is no heater control valve on the 1993s. They didn't start installing them until 1994.

 

[natenkiki2004]

Based on everything I've read and seen, there is no heater control valve on the 1993s. They didn't start installing them until 1994.

I would double-check just to make sure. Would be really silly to replace the heater core and chase an issue for a long time to find out the valve is stuck You should see the 2 hoses coming out of the firewall, if you can follow them straight to the engine block, there's no valve. The valve, at least on my 1994, has both hoses going to it and coming out of it but it's not that large, something that could fit inside a coffee cup.

 

[Zachj83]

I would double-check just to make sure. Would be really silly to replace the heater core and chase an issue for a long time to find out the valve is stuck You should see the 2 hoses coming out of the firewall, if you can follow them straight to the engine block, there's no valve. The valve, at least on my 1994, has both hoses going to it and coming out of it but it's not that large, something that could fit inside a coffee cup.

Just so I'm understanding correctly: I would follow the heater hoses out of the firewall, and if they hit a small valve before the block, then that would be the heater control valve. If they go straight into the block, then that would mean there is no valve and the problem would be somewhere in the firewall, presumably with the heater core?

 

[natenkiki2004]

Just so I'm understanding correctly: I would follow the heater hoses out of the firewall, and if they hit a small valve before the block, then that would be the heater control valve. If they go straight into the block, then that would mean there is no valve and the problem would be somewhere in the firewall, presumably with the heater core?

Correct. The heater valve will also have a small plastic vacuum line going to it as well. It's usually up on top or in front of the fan box and AC dryer.

 

[Zachj83]

Correct. The heater valve will also have a small plastic vacuum line going to it as well. It's usually up on top or in front of the fan box and AC dryer.

Thanks again for everything Nate. Going to check the heater control valve first, then move on to flushing the heater core, then PROPERLY (without letting air in) add coolant back into the system. Does that sound like the right way to go?

 

[natenkiki2004]

Thanks again for everything Nate. Going to check the heater control valve first, then move on to flushing the heater core, then PROPERLY (without letting air in) add coolant back into the system. Does that sound like the right way to go?

Sounds good. Though I gotta say, I've had my cooling system opened several times and never had issues bleeding the air out. Fill up the radiator, squeeze the hoses to burp it, put the cap on and fill the reservoir to the cold level. Let it run a heat cycle or two and then top off the reservoir.

 

[larrydd999]

From my experience the stability of the temperature gauge also depends a lot on the condition of the thermostatic fan unit. That wouldn't explain the heater problem, however.