No coolant flow to brand new heater core

[rcvxl24]

Hello everyone, long time first time. Starting a thread is usually my last resort, and well here I am.

Battling a no heat issue on my 1998 Limited V6 2WD. More specifically, I'll occasionally get some lukewarm heat, but after running the fan for half a minute or so it'll go cold.

Background:

• Coolant gage always sits barely below the middle
• Scanner says coolant is reaching ~188F
• The heat has never worked since I've owned it
• The tees that go to/from the rear heater have been plugged

Attempts to solve:

• Brand new Spectra heater core
• Verified blend doors are working correctly
• Verified heater valve was working
• Bypassed heater valve
• New OEM thermostat
• 5-10 system bleeds
• New Radiator Cap
• Back flushed new heater core
• Back flushed engine/radiator

Here's the interesting thing. I replaced a section of hose before the heater valve with clear tubing and saw that with the truck running, the coolant is just sitting there; virtually no flow into the heater core.

Also, the system is not building pressure. After running and getting up to operating temp, you can pull the radiator cap off (even the new one) with no problem.

Am I missing anything? I'm pulling my hair out.

 

[heat]

No mention of water pump.

 

[rcvxl24]

My logic is that if the water pump wasn’t working correctly, it would be overheating. This thing has never even thought about overheating as long as i’ve had it, even with AC on full bast in the summer.


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[alumarine]

I agree it's not the pump if it's not overheating.
It's not the pump that builds the pressure it's the coolant temp.
It's a circulating pump, not a pressure pump.
Do you know anyone with a 4runner or Pickup with the same motor so you could compare hose routing?

 

[pluton]

I agree it's not the pump if it's not overheating.
It's not the pump that builds the pressure it's the coolant temp.
It's a circulating pump, not a pressure pump.
Do you know anyone with a 4runner or Pickup with the same motor so you could compare hose routing?

I concur: Look at the hose routing.

 

[19963.4lsr5]

The pipe under the intake may be clogged. You could remove the Rad cap and blow some compressed air through it.


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[rcvxl24]

Thanks everyone. I have a ‘98 FSM on the way that I will use to confirm hose routing. I believe the heater core outlet goes to the line underneath the intake - can someone confirm?

To rule out air in the heater core (and confirm no system leaks) I have a cooling system vacuum refill kit on the way too.


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[alumarine]

Here's a coolant flow diagram for the 5VZ-FE.

 

[pluton]

Note: The above diagram shows an EGR valve, which does not exist on our 4Runners.

 

[19963.4lsr5]

Thanks everyone. I have a ‘98 FSM on the way that I will use to confirm hose routing. I believe the heater core outlet goes to the line underneath the intake - can someone confirm?

To rule out air in the heater core (and confirm no system leaks) I have a cooling system vacuum refill kit on the way too.


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With nothing wrong and a good Rad Cap all you should need to do is fill the Rad to the top and ensure the expansion tank is filled to the top mark and heat cycling the engine around three times does the rest.

With a cold engine, if you remove your Rad cap is coolant touching the cap?


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[brillo_76]

Note: The above diagram shows an EGR valve, which does not exist on our 4Runners.

Yes with an * that's sure not a diagram of a 4 cylinder that's a v6 so in some parts of the world maybe the EGR is there just not in the us and canada market.

 

[alumarine]

Yes with an * that's sure not a diagram of a 4 cylinder that's a v6 so in some parts of the world maybe the EGR is there just not in the us and canada market.

I believe you're right.

 

[gamefreakgc]

Are you 100% sure the heater valve is working? I don't mean the cable is moving, can you confirm that your heater valve is not just sealed shut and broken? They break pretty easy - every time I've taken off a heater line off the valve it has broken on me. That would be the only thing making sense that would stop coolant flow in its tracks but not block flow in the engine. By the way, I can also take my radiator cap off when it's 'warmed up' after 5-10 minutes. I CANNOT take it off when it's actually hot after driving for say, 20 minutes or more as it sprays out like a fountain. Yes I've done it by accident.

 

[brillo_76]

I believe you're right.

Sometimes I am... and when I am not, the other members correct me..

 

[19963.4lsr5]

Are you 100% sure the heater valve is working? I don't mean the cable is moving, can you confirm that your heater valve is not just sealed shut and broken? They break pretty easy - every time I've taken off a heater line off the valve it has broken on me. That would be the only thing making sense that would stop coolant flow in its tracks but not block flow in the engine. By the way, I can also take my radiator cap off when it's 'warmed up' after 5-10 minutes. I CANNOT take it off when it's actually hot after driving for say, 20 minutes or more as it sprays out like a fountain. Yes I've done it by accident.

I’m pretty sure he mentioned bypassing the heater valve. That’s why I suggested the pipe under the intake is blocked

I know his problem is legit, but it makes no sense.


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[brillo_76]

Even if the IAC valve hose clogged, if I am looking at the flow diagram properly, it looks like that port and the heater port are shared on the casting. Maybe I am wrong.

I just wouldn't think they have anything restricting that heater core feed except the heater core control valve. As folks would want heat as soon as possible, this is probably why the port is where it is.



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[rcvxl24]

Quick update: like gamefreak mentioned, I was able to get the system up to pressure after driving around a little bit (still cleaning coolant out of all the crevices [emoji23]).

And as I mentioned in the original post, the heater valve has been bypassed.

I studied that cooling system diagram before starting this thread and while it is good enough to give me a general idea of the circuit, the arrows are so poorly drawn that it leaves me scratching my head when I try to put together exactly whats going on.

I plan on putting some work into it this weekend.


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[brillo_76]

I agree it's definitely a head scratcher for sure.

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[spartacus]

Hello everyone, long time first time. Starting a thread is usually my last resort, and well here I am.

Battling a no heat issue on my 1998 Limited V6 2WD. More specifically, I'll occasionally get some lukewarm heat, but after running the fan for half a minute or so it'll go cold.

Background:

• Coolant gage always sits barely below the middle
• Scanner says coolant is reaching ~188F
• The heat has never worked since I've owned it
• The tees that go to/from the rear heater have been plugged

Attempts to solve:

• Brand new Spectra heater core
• Verified blend doors are working correctly
• Verified heater valve was working
• Bypassed heater valve
• New OEM thermostat
• 5-10 system bleeds
• New Radiator Cap
• Back flushed new heater core
• Back flushed engine/radiator

Here's the interesting thing. I replaced a section of hose before the heater valve with clear tubing and saw that with the truck running, the coolant is just sitting there; virtually no flow into the heater core.

Also, the system is not building pressure. After running and getting up to operating temp, you can pull the radiator cap off (even the new one) with no problem.

Am I missing anything? I'm pulling my hair out.

I am not sure if this would help but the part# for 96-98 is 87240-35050 and the part number for 99+ is 872403-5070.

 

[rcvxl24]

So I think I’m one step closer to solving. I got the vacuum coolant refill kit snd it works great, confirmed the system has no leaks and is bled well. But did not solve the issue.

An additional symptom that I’ve been able to consistently recreate is that the heater upon startup/idle will actually works pretty good, but as soon as I start driving and (presumably) the thermostat opens up, the heat goes away.

I also pulled all the coolant lines between the engine and heater core to check for any blockages. No smoking gun, but while all the hoses were off i did stick a 14gauge solid wire as far down into the coolant bypass (under the intake) as i could and when i pulled it out it was filthy with a bunch of crap on it. When i bought this truck a year and a half ago the coolant looked absolutely atrocious and had tons of gunk everywhere, so this is not surprising.

To me, this is seeming like a clogged coolant bypass. My valve cover gaskets are leaking oil, so I’m seeing this as a great opportunity to replace those and inspect the bypass while I’m in there. I will order parts for that job this week.


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