Another No Heat/Warm heat thread.. please help troubleshoot

[pungo]

Have you tried using an IR temp gun to check the temps going to the heater intake and the outlet when the valve is both open and closed?

The inlet and outlet heater core hosed read about 110F which is about the same the radiator top hose.

With the valve open the temp drops to the about 80F.

I'm thinking to repair the leaking tube on the firewall (with a section of rubber hose) for the rear heater core to see if I can get some heat out of the rear heater.

 

[heat]

top rad hose should read higher than that. you're over-cooling, like the
'stat is stuck open.

 

[WWRD99]

I'll check mine again but I'm pretty sure my upper hose is close to 170 to 180 warmed up with the cap on...heater core hose should be about that too as the thermostat is a 185 open status...+ or - a few...I know you wrote you used a new toyota thermostat...not sure how you could have an over cooling system as the thermostat should set the temp and keep it there...I know a stuck open thermostat will eventually over heat but easier in the summer...might not in the winter...could be you got a bad new thermostat...kinda stuck at the basics with this one that drive people crazy...even that though with 110 core temps it should have some heat which makes me think the blend door that does hot and cold is stuck open to cold...when I did my heater core this summer I replaced the foam on the blend doors since a good bit had fallen off...has a tight seal...did you happen to notice that the foam at the doors not sealing tight?

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[Kotletachka]

Yes, make sure you clean the entire cooling system well. Don't forget the rear heater lines. Do you plan to keep the runner for few years? if then it won't harm to get a new radiator. I saw somewhere the Denso radiator is at US$104. Not sure how it is going to be when it crosses the border.

Flush the rear lines ALOT. They hold alot of junk. Used compressed air and water.

 

[alumarine]

My top rad hose is 167 measured on the rubber hose close to the outlet and 153 measured on the aluminum outlet itself.

Heater hose inlet is 146 and outlet is 143.
That's with the fan off.

I had only been running about 30 minutes and it's 32 degrees F here.

The inlet and outlet heater core hosed read about 110F which is about the same the radiator top hose.

With the valve open the temp drops to the about 80F.

I'm thinking to repair the leaking tube on the firewall (with a section of rubber hose) for the rear heater core to see if I can get some heat out of the rear heater.

 

[pungo]

My top rad hose is 167 measured on the rubber hose close to the outlet and 153 measured on the aluminum outlet itself.

Heater hose inlet is 146 and outlet is 143.
That's with the fan off.

I had only been running about 30 minutes and it's 32 degrees F here.

I'll take some more measurements now that it's above freezing. When I measured them initially, it was in the low 20s F.

 

[pungo]

top rad hose should read higher than that. you're over-cooling, like the
'stat is stuck open.

I took the measurement with the temps were in the low 20s. I'll take some new measurements now that it's above freezing.

I don't hink I'm over cooling, the temp gauge is in the middle and the obd reader shows 195.

 

[pungo]

I'll check mine again but I'm pretty sure my upper hose is close to 170 to 180 warmed up with the cap on...heater core hose should be about that too as the thermostat is a 185 open status...+ or - a few...I know you wrote you used a new toyota thermostat...not sure how you could have an over cooling system as the thermostat should set the temp and keep it there...I know a stuck open thermostat will eventually over heat but easier in the summer...might not in the winter...could be you got a bad new thermostat...kinda stuck at the basics with this one that drive people crazy...even that though with 110 core temps it should have some heat which makes me think the blend door that does hot and cold is stuck open to cold...when I did my heater core this summer I replaced the foam on the blend doors since a good bit had fallen off...has a tight seal...did you happen to notice that the foam at the doors not sealing tight?

Prior to installing the new thermostat, I tested it in hot water on the stove using a thermometer and verify it started opening at 180 and fully open by 190. I cycled it several times and it worked as designed. I always do this prior to installing a new thermostat. I have seen I few out of spec, but never a Toyota one. The only thermostat failures I've ever seen were stuck closed, not open.

I thoroughly checked the operation of the blend doors while I had the heater box on the bench and the doors worked perfectly. I triple check the blend doors operation after installing the heater box and cables. The foam was in good shape, though even if the foam was completely missing, I should get more than cold air blown out, just not as efficient.

The obd reader read 195 and the temp gauge is in the middle so I think the thermostat is working properly.

 

[WWRD99]

Something is not measuring up right, It's impossible for the hoses to be 110 degrees with the thermostat open at 190 degrees...the heater core hoses should be real close to that temp as well...the upper hose might be 10 to 15 less than input temp but that's still no where close to 110.

 

[19963.4lsr5]

Did you ever replace the rad cap? If it’s not venting properly during warm up and cool down you may have an air pocket. Even with you big funnel in the rad.

Try a new rad cap if you didn’t. And do some spirited accelerations with the heat on to open the heat valve to try and push any air that may be trapped in the core. That heat valve is the high point. If air can’t push to the rad and vent out the cap to the expansion tank I could see it causing your problem.

After you drive it and it cools off and remove the rad cap....is there coolant touching the bottom of the cap or is there an air pocket?


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[pungo]

Something is not measuring up right, It's impossible for the hoses to be 110 degrees with the thermostat open at 190 degrees...the heater core hoses should be real close to that temp as well...the upper hose might be 10 to 15 less than input temp but that's still no where close to 110.

When I was taking those measurements on the hoses the outside temps were in the low 20s, so maybe the ambient air was cooling the outside of the hoses. I'll take some more measurements, now that it's in the 50s.

Did you ever replace the rad cap? If it’s not venting properly during warm up and cool down you may have an air pocket. Even with you big funnel in the rad.

Try a new rad cap if you didn’t. And do some spirited accelerations with the heat on to open the heat valve to try and push any air that may be trapped in the core. That heat valve is the high point. If air can’t push to the rad and vent out the cap to the expansion tank I could see it causing your problem.

After you drive it and it cools off and remove the rad cap....is there coolant touching the bottom of the cap or is there an air pocket?

I installed a new Toyota cap when I replaced the radiator. I have tried the old cap as well. The coolant is touching the bottom of the cap once the vehicle cools off. Been driving it for a few months after the coolant system work, so plenty of spirited accelerations getting on the highway. The expansion tank level changes when hot or cold, so I assume the cap is working properly.

 

[BikeIdiot]

Same Issue

I am fighting the exact same issue. I have a 97 4runner with 290k. I used to have excellent heat. Now my heater works good but not great. I drive 60 miles to work each morning. Once I start driving the heater becomes noticeably warmer and blows hot after the engine is fully warmed up. After 30 minutes the heat is gone and I have cool air blowing. If I turn off the fan, wait a minute, and then turn the fan back on, I have hot air for about 15 seconds. I can do this over and over all the way to work.

I have done the following:

1. New heater core
2. New thermostat.
3. New coolant (Toyota red, properly diluted).
4. Parked on incline and burped system
5. Verified all control cables connected properly on back of control unit.

The heater system is not complicated and I am at a loss for an explanation.

 

[BostonJon]

I am fighting the exact same issue. I have a 97 4runner with 290k. I used to have excellent heat. Now my heater works good but not great. I drive 60 miles to work each morning. Once I start driving the heater becomes noticeably warmer and blows hot after the engine is fully warmed up. After 30 minutes the heat is gone and I have cool air blowing. If I turn off the fan, wait a minute, and then turn the fan back on, I have hot air for about 15 seconds. I can do this over and over all the way to work.

I have done the following:

1. New heater core
2. New thermostat.
3. New coolant (Toyota red, properly diluted).
4. Parked on incline and burped system
5. Verified all control cables connected properly on back of control unit.

The heater system is not complicated and I am at a loss for an explanation.

have you tested or replaced the heater valve mounted to the firewall?

 

[BikeIdiot]

have you tested or replaced the heater valve mounted to the firewall?

It opens and closes as it should.

 

[19963.4lsr5]

I can see those aftermarket heat valves do something dumb when the plastic gets hot.

Normally no heat is air in he heater core or low on coolant.


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[mpp917]

sorry to start up an old thread and hopefully you have solved the problem by now...but in case you haven't or someone else has the same problem...I have a 98 with a similar problem. There is a control arm on the bottom of the heater case that controls a blend door that is susceptible to drunk friends breaking with their feet, and when they do, you lose some control over temperature blending. The air comes out of my center vents (defrost, feet, and face) luke warm, but the air on the side vents comes out desired temp. This could be your problem, it may not. The solution is to find a new heater case and install it (might as well swap heater core while you are at it), which means taking the dash apart. I have included a picture of what it should like above the passenger footwell. Hope this helps!

 

[Litedog]

I had the same problem. I found the sheath for the cable to the blend door had broken and the blend door wasn't opening. I used Gorilla tape to tape the sheath together and it is working again.

In the picture above, it is the cable just above and to the left of the yellow circle. The sheath was conveniently broken right about 6" from the rusty clip in the picture, so it was an easy repair. We'll see how long it lasts.

 

[Johnin714]

I had the same problem. I found the sheath for the cable to the blend door had broken and the blend door wasn't opening. I used Gorilla tape to tape the sheath together and it is working again.

In the picture above, it is the cable just above and to the left of the yellow circle. The sheath was conveniently broken right about 6" from the rusty clip in the picture, so it was an easy repair. We'll see how long it lasts.

This actually worked for me. Simple but it worked thank you for pointing this out!

 

[georunner_sjc]

Hello all, great thread. I’ve just had my heat from the front controls go south. Blower motor works, but the temp slider seemingly has no effect on the air temp from the vents. Which is blowing cool air, not heated air.

The rear heater does work, and is pushing warmer air. It’s set at the hottest point, but seems it could be warmer…

Would popular/expert opinion point to a thermostat issue?

Thanks for any guidance here folks!

1996 Limited 4WD

 

[brillo_76]

I would suspect a few things:

Being you are getting some heat I the rear.

I would make sure your antifreeze is at the proper level.

I make sure the thermostat is working properly as if it's stuck open. You probably wouldn't get much heat.

I would verify the heater valve which is right above the engine with the hoses goto heater core cable is connected and working.


Then goto the bottom of the heater core box inside the truck and verify the cable is connected and moving properly

If all that is working properly. Then it would be a plugged heater core.

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