Heat Only Working in First Few Seconds of Turning Fan On

[SendDerek]

This is a problem on a 1997 4Runner Limited with 200,000 miles. The mechanics that I've visited in town with are clueless -- let's see if you guys have some other ideas. I had one mechanic take a look, and he replaced the thermostat which seemed to work very well until half hour later when I was on the highway. Ever since I've had no heat except for the few seconds immediately after I turn the fan on (with the heat cranked). Within 5 to 10 seconds, it's freezing cold again. If I then turn off the fan and drive for another block or two, I can feel heat when turning it back on, but again, only briefly.

Here's what I know:

1. The thermostat is new.
2. The coolant was flushed within the last 5K miles.
3. The valve that sits behind the firewall and is connected to the heat lever is moving as it should.
4. I don't have any record of the water pump being replaced.
5. There is not any coolant smell nor is the passenger floor soaked (it's moist, but might be irrelevant -- does not smell like coolant).
6. Rear heater is cold also.
7. It's cold if I'm recirculating or bringing air from the outside.
8. Hoses on either side of the valve are hot (100 degrees) and radiator hose is hot.
9. Air blows strong, just no heat.
10. Temp gauge reads normal.
11. Not overheating (on the highway with many steep ups and downs @ 80MPH no issues).
12. I'm no mechanic.
13. I have not taken a water hose to the heater core to try and flush things out. Mechanic swears heater core is okay, so I have not had a huge push to do this.
14. I can hear slushing sounds coming from behind the dash somewhere when stepping on the gas from a stop.
15. No coolant leaking occurred on the floor when doing a pressure test at the mechanic.
16. No sign of head gasket leaking when doing a pressure test at the mechanic.
17. Coolant levels are good. Reservoir is about half-way filled will coolant as well as the radiator.

I read somewhere that it's possible that the water pump blades are going bad, but the vehicle is not overheating. From what I read here, this doesn't make a lot of sense. BUT, from what I read here, it seems like it might be an alright thing to check?

It's as if the heat is being stored in a box somewhere and then being depleted very quickly when turning on the fans. Then, it fills back up with hot air in the time that I have the fan off, and starts the cycle all over again when turning on the fans again.

I did attempt to jack up the front, open radiator cap, and start the 4runner. I saw one bubble raise out and then quickly the coolant started to overflow on the top. I put the cap back on as soon as that happened. I may need to repeat this again depending on what you guys might say is the correct way to do it.

Thanks for your help in advance. It's greatly... GREATLY appreciated.

 

[TheDurk]

Digital Control? Have you run the self diagnostic routine? Probably the climate control temp sensor. A few threads in the last few weeks. I'll come back with a link.

EDIT: Here you go:http://www.toyota-4runner.org/3rd-gen-t4rs/81640-auto-climate-control-2001-only-blows-really-hot-really-cold.html

 

[SendDerek]

I sure appreciate the quick response, but the link you provided doesn't tackle the same issue. They describe having ONLY hot or ONLY cold air and nothing in between. I'd be fortunate enough to have that problem at this stage of the game.

It's a '97, so no digital controls, just the good 'ol fashioned levers with cables attached.

 

[SendDerek]

More information...

Additional details (after a quick, midnight drive around the block and on the highway shortly):

• The rear heater behaves the exact same as the front.
• After checking this thread, the second cable under the glovebox seems to be operating correctly. I tried to use my hand to see if it would "push" any further, and it doesn't.
• When turning to cold air and then turning on the fan, it spits out cold air immediately.
• I checked the fuses under the hood. All seem okay. Should I test the relay somehow? Not sure if this is the problem since I am getting heat, just not for very long...

 

[Singtoe]

Sounds like the heater control valve that is located between the firewall and the engine has crapped out on you.

 

[SendDerek]

If I'm thinking right, isn't that the valve that's attached to the firewall on the engine side, near the top? When you slide the heater control left to right, I can visually see the cable move the arm on the valve left to right. From the looks of the image (thanks, by the way), it appears we're talking about the same thing. I did mention before that the hoses on either side of that valve are hot (~100 degrees). Is it still possible that this valve is broken internally?

This is an image from an older model 4Runner:

We are talking about the same thing, right?

Also, does this control the rear heating as well, or is that have it's own heater control valve? I'm still trying to link together why each of the heaters are acting the same way.

 

[TheDurk]

I sure appreciate the quick response, but the link you provided doesn't tackle the same issue. They describe having ONLY hot or ONLY cold air and nothing in between. I'd be fortunate enough to have that problem at this stage of the game.

It's a '97, so no digital controls, just the good 'ol fashioned levers with cables attached.

I knew the issue was different, but the diagnostic would have been worth the effort if you had the digital. Mine is manual, too. Yours is a head scratcher. I think I'd try burping again--air lock seems logical given that problem began since recent flush and the sloshing sound you hear. I assume you did your first burping with the heater full on?

I would think you could pull that control valve and see if it is not opening or obstructed in any way. You could even straight pipe it as a test. I have seen one look normal but the shaft was broken inside (but on a Mercedes).

 

[SendDerek]

I don't think I did the burping correctly the first time (I cannot confidently say where I had the heater controls). Besides, all I did was prop it up on a curb and open the radiator cap to see one bubble before it started to overflow. Since then, I've seen several different methods for doing it, but I'm not sure which is the best.

Do the 3rd gens have a release stem/bold? Here's a helpful video that seems to do a good job of explaining exactly how to purge the air bubbles from the coolant system:
YouTube - How To Bleed A Cooling System

Another simple set of instructions from a forum post:
http://www.toyota-4runner.org/maintenance/13873-coolant-refill-air-bleeding.html#post123829

Lucky enough for me, the mechanic I mentioned in the first post is willing to try this procedure for free (he's never done it before, so it's going to be a "training" exercise for him). Monday is the big day, so I'll let you know what happens. If there are any suggestions that I need to hand down to him, please let me know. You may know something specific to the 4Runner air purging procedure that he doesn't know about and I haven't read about.

I will also bring up bypassing the heater valve with a straight pipe. He mentioned that he has never seen one break internally, but that doesn't mean it's impossible.

I was driving it around on my lunch hour today and noticed the gurgling/slushing sound wasn't there. I wonder if this went away after filling both the reservoir and radiator to proper coolant levels. Before, I know that the reservoir was bone dry when the vehicle was cold. I'll keep my ears open... it's gonna be a long, anticipation-filled weekend.

 

[SendDerek]

Updates

The vehicle just got out of the mechanic's shop after an attempt to purge the air bubbles. Unfortunately, this didn't resolve the issue. 30 degrees, snowing, a 3 year old in a child seat in the back, and still no heat...

My next thought is, is it possible that the internals of the heater control valve are broken (remember that both the hoses coming from either side of the valve are hot)? I've asked this before, but haven't received an answer. I suppose it would be easy enough to tear into this part and see for myself (might have some coolant spill over and make a mess, but it's okay in the name of science). Another thing to remember is that the rear heater is behaving the same way (is there a link/relationship here?).

Now that I have paid more attention to the problem, here's my next theory: when the fan starts to blow, a valve (or redirection panel) somewhere is open to begin with, but then because of the air flow, it moves into a closed position, leaving me with cold air coming in. This might explain why I get hot air, but then quickly get cold air due to a valve closing or turning in a different direction than what it should be due to the airflow. If I turn the air down again, drive for a block or two, and turn it back on, it's just enough time for the valve to fall back into it's normal spot and redirect the warm air into the cab before moving back again.

I'm hoping somebody can comment on the new observations. Any advice would be greatly appreciated.

 

[SendDerek]

Another observation...

One more observation... maybe it will help put a nail in this thing. When I have the fan control turned to the "OFF" position and the vehicle is moving, I can feel some good heat coming from the vents. When I turn on the fan, it becomes simply gets cold after 10 seconds or so.

If I were to rip apart the dash board and take a look behind the HVAC controls, what should I be looking for? Maybe a cable was disconnected when I re-installed the stereo?

Any ideas yet? Does anybody have a good diagram for the area of the system I should be looking at?

Thanks in advance.

 

[cfranck1]

Take a look at the picture. Its from the passenger floor, looking up under from behind the center dash. See the eye-lit cable to the right of picture? Its disconnected from the white piece that moves your blend door and it SHOULD BE connected. Check if yours is the same way. Or see if you see any other cables disconnected under there. IF not i would check behind the center heater controls to see if anything is loose.

Other than that. It might sound like a bad (clogged) heater core.

 

[SendDerek]

I really appreciate your time. I have already checked that particular cable, and it's connected properly.

It doesn't sound like it takes that much time to flush the heater core, but my concern is that both hoses on either side of the heater control valve are hot and the same temperature. If it was a blocked heater core, wouldn't one of these cables be cooler than the other?

 

[cfranck1]

I really appreciate your time. I have already checked that particular cable, and it's connected properly.

It doesn't sound like it takes that much time to flush the heater core, but my concern is that both hoses on either side of the heater control valve are hot and the same temperature. If it was a blocked heater core, wouldn't one of these cables be cooler than the other?

You said both sides of the control valve are hot but try to grab both sides of the heater hoses that actually go to the heater core. They should be on the left side of the valve on the firewall.

Maybe the installer put the T-stat in backwards? or the Jiggle valve on the t-stat is mounted up instead on downwards.

 

[SendDerek]

Thanks! I hadn't realized I was looking in the wrong place. By any chance, is there an annotated image to point me in the right direction? I'm afraid my eyes aren't very keen to what's what... I would like to flush the heater core with the water hose but want to know for sure what hoses are what. That would be greatly appreciated.

 

[cfranck1]

Thanks! I hadn't realized I was looking in the wrong place. By any chance, is there an annotated image to point me in the right direction? I'm afraid my eyes aren't very keen to what's what... I would like to flush the heater core with the water hose but want to know for sure what hoses are what. That would be greatly appreciated.

See if this picture helps you get a better idea?!

 

[SendDerek]

That's a huge help. I will be taking a look after work tonight and see if I can make sense of it. It's interesting to try to read this diagram however. The hose marked 87246E leads to... nowhere? haha.

Is it possible that the part labeled 90467-23009 attached to the hose labeled 87246E comes back and attaches to 87245A (other side of the heater control valve)? Are these numbers simply part numbers or reference numbers?

Also, I saw that you edited your post recently with t-stat instructions. I will for sure check this out as well. Thank you for your patience and help.

 

[cfranck1]

That's a huge help. I will be taking a look after work tonight and see if I can make sense of it. It's interesting to try to read this diagram however. The hose marked 87246E leads to... nowhere? haha.

Is it possible that the part labeled 90467-23009 attached to the hose labeled 87246E comes back and attaches to 87245A (other side of the heater control valve)? Are these numbers simply part numbers or reference numbers?

Also, I saw that you edited your post recently with t-stat instructions. I will for sure check this out as well. Thank you for your patience and help.

Part # 90467-23009 are hose clamps for the hoses.
I think they are reference numbers 87246a and 87246e go to either the intake and a steel heater hose not the heater valve.

 

[SendDerek]

Thanks again for the help. I had a glimmer of hope tonight after I flushed the heater core with a garden hose... it was actually warmer than it has been since the whole fiasco started. Eventually, the hope faded into cold air. This time it took a LOT longer to do. I also noticed that the heat seemed to depend on the RPMs when I put the 4Runner in neutral. In other words, at idle, it was cold, but when I got to 4 to 5K RPM, it was much warmer (not hot, just warm). After a while of driving around, it got cold again. I can tell I introduced some air bubbles into the system because I hear a slushing sound from behind the dashboard.

I'm assuming the garden hose didn't have quite enough "oomph" to kick out all the nasty stuff. I'd like to get it to a place that has an air compressor and do it that way (and then once again purge the air bubbles).

One last observation... it seems like the windows fog up rather quickly. It's 30 degrees outside still and maybe it's just our warm bodies when we get into the 4Runner, but I've heard to be cautious about foggy windows when you're having issues with the heater core. Is this true? Should I be concerned?

 

[cfranck1]

One last observation... it seems like the windows fog up rather quickly. It's 30 degrees outside still and maybe it's just our warm bodies when we get into the 4Runner, but I've heard to be cautious about foggy windows when you're having issues with the heater core. Is this true? Should I be concerned?

Yes you should be concerned. That is one of the major signs that your heater core has or is going..

Some of the symptoms of a bad heater core are:

Your radiator is full of fluid, the thermostat works fine, but you still have no heat.

You find a puddle of antifreeze on the passenger side footwell inside the car.

You smell antifreeze when you run the heater or defroster.

You see puffs of smoke coming out of the defroster or vent ducts.

Your windshield fogs up during or after you run the heater/defroster.

 

[SendDerek]

Great news! The heat is working terrific! It's almost TOO hot! haha. Just kidding of course.

A buddy of mine has an air compressor, so we used that (120 PSI or so) and did a back flush on the heater core. It was most effective of getting the junk out of the core when it had some coolant inside. We rigged up a garden hose (to catch the coolant and gunk in a garbage can) on the hose going into the heater core and blew the air into the hose coming out. When there was no more liquid blowing out of the hose, we clamped the hoses back on, ran the truck for a minute, disconnected the hoses, reconnected the garden hose, and repeated three times.

Again, it's working great now! Took less than an hour to do it. I'm not noticing the fogging anymore, but will keep my eye on it.

Thanks so much cfranck1 for pointing me in the right direction as far as the heater core hoses. Thanks to everybody else for you time and efforts as well! The wife and kid thank you too.