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Unread 07-16-2005, 03:35 PM   #1
Jeepsrfun
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Coolant Flow

I'm a little confused here (o.k. way more than a bit). I have the Haynes Wrangler manual and I'm not sure what to make of the coolant flow pictures.

On a 99 4.0L TJ, is the coolant flow independent of the heater core, or does it route through the heater core. According to the Haynes manual, some of the engines look like the heater core is plumbed in so that the return route is through the heater core. If it was electrical, I would say it's in series, instead of parallel.

The diagram for 4.0L 1991 and later is pretty lacking in detail, so is my coolant path depending on flow through the heater core (which may be gunked up) or is it plumbed in parallel with everything converging at the water pump, thermostat housing area?

Thanks,

Dad

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Unread 07-16-2005, 03:40 PM   #2
Jerry Bransford
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The coolant flows through the heater core but only when the heater's temperature control is up from the no-heat position. The heater's temperature control controls a valve that controls the flow of coolant through the heater core. So if the heater's temperature control is in the Cold position, no coolant flows through the heater core.
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Unread 07-16-2005, 03:56 PM   #3
ozntz
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is it mine then because i notice heat when its set to cold if i don't have the fan on?
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Unread 07-16-2005, 03:58 PM   #4
Jeepsrfun
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It the core is blocked or the valve sticks, do I still have flow for the engine?

And where's this valve? That might be why I have no heat out the vents???


Dad


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Originally Posted by Jerry Bransford
The coolant flows through the heater core but only when the heater's temperature control is up from the no-heat position. The heater's temperature control controls a valve that controls the flow of coolant through the heater core. So if the heater's temperature control is in the Cold position, no coolant flows through the heater core.
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Unread 11-10-2005, 09:32 AM   #5
MikeWL
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I'm wondering if the heater core flow valve might be my problem.

I seem to have little or no flow to the heater core at low RPM's. I start the Jeep for 10 minutes before leaving in the morning with the heater set to high and when I get in it's still blowing cold air. A few rev's of the engine and the air gets warm almost instantly, but if I let it idle for a bit, the air slowly returns to cold.

I see an electrical connection to the thermostat housing where the heater core hose comes off, is that where the valve is? I suppose it could be stuck or not opening fully and only the increased pressure from higher RPM's would allow the flow. ???? Anybody seen this before? I guess I'll rip into it this weekend.
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Unread 11-10-2005, 01:00 PM   #6
scorpionkill
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Yeah, where is this valve. I never heard of such a thing. I have a 1997, I thought coolant flowed through the heater core at all times and the blend door just diverted the air when you selected the cool air option.
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Unread 11-11-2005, 10:03 AM   #7
Jeepsrfun
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Let me know if you find it. I'm still looking for it. Same symptoms. Not much heat through heater until a fair bit of time at highway speed (10 minutes or so). Flow through heater core seems o.k., although I'm going to let a radiator shop flush it for me. Running 1 (no more than 2 needle widths) below 210 on the temp gauge. Defroster pretty much overwhelms the heater, even when set to full hot.


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Quote:
Originally Posted by scorpionkill
Yeah, where is this valve. I never heard of such a thing. I have a 1997, I thought coolant flowed through the heater core at all times and the blend door just diverted the air when you selected the cool air option.
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Unread 11-11-2005, 10:35 AM   #8
JFM626
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I must confess I have no idea what if anything controls the coolant flow through the heater core on a 99. On my '04 though the coolant appears to flow through the core as soon as the engine is fired up. You can test for this by holding onto the heater hoses with the heater temp set to cold. If both hoses get hot to about the same temperature, then the coolant is circulating through the heater core. If only one hose gets hot, and the other remains cold, then there is a shut off/blockage somewhere in the system.

Try running the heater on hot without the fan, if the coolant in each hose remains about the same then there is some flow through the heater core. Now turn the fan on high and check the hoses again, if one now is clearly cooler, than the flow may be slowed down by an internal partial blockage and should be flushed.Other possibilities exist as well of course, such as heater hose(s) collapsing internally, or even a water pump. If however the heat in the hoses is about the same I would suspect that the heater core is blocked externally with duff of some sort

The direction as to where the heat goes seems to be controlled by vacuum, as I can hear it inside the cab.
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Unread 11-11-2005, 07:48 PM   #9
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Well, I did a quick test of mine this morning and it seems to be functioning properly now. This is after I disconnected the core hoses and flushed with the garden hose. But the real test will be when we finally get a nice cold morning to test it.

I found out that the little fitting on the waterneck is the coolant temperature sensor. I'm beginning to think the water flows to the heater core all the time. My service manual has no reference to a valve.
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