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Which heater hose is under pressure, which is return line?

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#2 ·
In a warmed up system (T-stat open) the system should be neutral (same pressure everywhere)

On a cold system warming up (before T-stat opens) the upper hose may appear to be hard and under pressure.
 
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Discussion starter · #3 ·
I am putting cut off valve in system. It is nonsense in AZ to have a hot heater core in the interior. I bought two valves but I was hoping to just put one valve on one side. Seems like both lines should have valves to avoid pressure build up in heater core?

I looked at the "old" way with the built in vacuum operated valve on older XJ's at the junk yard. Those valves were in place on both lines.

What do you think? Two valves?
 
Discussion starter · #5 ·
Sure NOW you tell me....

Did two while I was there. In a few weeks will be doing a/c evap core and was going to replace hoses anyway. Figure this was good time to play. Am planning on new heater hoses anyway. Then I will put one back on with no valve.

Now for some pictures. Closed and opened.

Image


Image
 
#6 ·
If you want zero pressure/zero leaks on/in the heater core, you need two valves.....one valve in each heater hose. Using one valve will eliminate flow but the heater core will still see the same pressure as the rest of the cooling system. Also, the t-stat does NOT make a water tight/pressure tight seal.
 
Discussion starter · #7 ·
So two valves is good idea?

Also the barb ends IF anyone wants to do this, remember the hoses are different sizes internally. I needed 5/8 barbed ends and 3/4 inch barbed ends. Used 1/2 inch ball valves.

By the way, the nice cool outside are is now nice and cool inside air through the vents. No heat "leaking" from the heater core/blender door design into the outside air/vent.
 
#8 ·
Um...maybe it is just too early for me, but can someone explain to me how this is not a horrible idea? The way you appear to have your valves set up, you are not pumping any coolant through your system (not just the heater core... the whole system). The factory heater control valve RE-ROUTES the flow of coolant to bypass the heater core. What I see there is a total elimination of the flow. This just seems wrong to me....
 
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#9 ·
if you put two valves in, the pressure can build up in the heater core. You only need to stop the flow, and one valve will do it. You will get way more heat radiating through the fire wall than what would work its way transfering up the hose with no valve on it.
 
#10 ·
TheNerd said:
Um...maybe it is just too early for me, but can someone explain to me how this is not a horrible idea? The way you appear to have your valves set up, you are not pumping any coolant through your system (not just the heater core... the whole system). The factory heater control valve RE-ROUTES the flow of coolant to bypass the heater core. What I see there is a total elimination of the flow. This just seems wrong to me....
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^^^I agree 100%^^^

The old vacuum operated XJ valves did just that, RE-ROUTE the flow, not obstruct it.

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Obstructing the flow will be the result of just 1 valve, or 2. It makes no difference.

DON'T DO IT! :thumbdown:

Max :cheers2:
 
#11 ·
If you put a t in each hose and connect with a valve, you car send the coolant back to the engine by opening a valve betweent the t's and make flow through the core exactly zero by putting a valve on one of the heater core hoses. This way you never get a pressure buildup in the core.
 
Discussion starter · #12 ·
"not pumping any coolant through your system"

Sorry but that is incorrect. The entire coolant flow does NOT go through the heater core. A small amount of radiator flow goes through the heater core. You do not want to allow pressure to build in the core as it will encourage leaks. The reason it was rerouted is for that same reason. Not that the entire coolant flow is routed through the heater core. I carefully examined an "older" cut off valve to be sure. Two valves accomplish the same end. No flow and no pressure through the heater core.

Valves opened to flush core, making sure there is clean antifreeze in it, valves off. Engine cooling just fine. Will be like this until maybe even November this year.

Or do some of you folks believe the entire coolant flow goes through our tiny heater core hoses and the heater core?

The difference is quite worthwhile. Cool outside air stays as cool outside air.
 
#13 ·
Jeepaddict said:
if you put two valves in, the pressure can build up in the heater core. You only need to stop the flow, and one valve will do it. You will get way more heat radiating through the fire wall than what would work its way transfering up the hose with no valve on it.
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Wrong.....the OP has a '97 XJ which does NOT have a factory water flow control valve to/from the heater core. Seeing the OP's pics, he has correctly isolated the heater core from both cooling system pressure and flow by using two valves. If he had used only one valve, in either hose, he would eliminate flow but not pressure.:thumbsup:

I would strongly recommend opening both valves frequently for a few minutes with the engine idling so that coolant/anti-corrosion can circulate through the heater core. Stagnate/non-flowing coolant is not a good thing.
 
#14 ·
djb383 said:
Wrong.....the OP has a '97 XJ which does NOT have a factory water flow control valve to/from the heater core. Seeing the OP's pics, he has correctly isolated the heater core from both cooling system pressure and flow by using two valves. If he had used only one valve, in either hose, he would eliminate flow but not pressure.:thumbsup:

I would strongly recommend opening both valves frequently for a few minutes with the engine idling so that coolant/anti-corrosion can circulate through the heater core. Stagnate/non-flowing coolant is not a good thing.
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:thumbsup: Agreed, as well as the letting the coolant flow occasionally.

You really only need one valve, for stopping the circulation. It won't build up pressure, or hurt anything to have the heater core feed lines closed. That's basically what is happening when the engine is cold and the T-stat is closed on the main cooling system.

The H20 Pump is a "loose" system, meaning it can't blow itself apart if something is clogged...it just simply won't circulate any coolant and in a way just cavitates. Like a fuel system that doesn't have a return line. The pump keeps the pressure there but there is enough slop in the system to not blow anything out.

:cheers2:
 
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Discussion starter · #15 · (Edited)
"Stagnate/non-flowing coolant is not a good thing."

That's what I keep telling my wife but she still insists I go outside when de-stagnating my coolant.

It'll be flushed well and filled with properly proportioned coolant and then shut off until its needed. I will bet the Cherokee all will be well.

Edit: Seems to me some folks are missing the point. The point is to get a HOT heater core in the cabin that is HOT all the time to no longer be HOT. The idea that by design there is a HOT device inside the cabin 100% of the time is hard to understand. The air blend door is ok for what it is but the system is not air tight. Air bleeds through the heater core. By eliminating a HOT core in the cabin means the A/C has a little less work to do and out side air does not get warmed on its way through the HVAC box.

By being in the middle of rebuilding my HVAC box it became clear anything that can stop the heater core from being HOT 100% of the time, at least here in Arizona, is a good thing.

And in case anyone is interested, total cost was just over 13 bucks.
 
#16 ·
jsmiddleton4 said:
"Stagnate/non-flowing coolant is not a good thing."

That's what I keep telling my wife but she still insists I go outside when de-stagnating my coolant.

It'll be flushed well and filled with properly proportioned coolant and then shut off until its needed. I will bet the Cherokee all will be well.

Edit: Seems to me some folks are missing the point. The point is to get a HOT heater core in the cabin that is HOT all the time to no longer be HOT. The idea that by design there is a HOT device inside the cabin 100% of the time is hard to understand. The air blend door is ok for what it is but the system is not air tight. Air bleeds through the heater core. By eliminating a HOT core in the cabin means the A/C has a little less work to do and out side air does not get warmed on its way through the HVAC box.

By being in the middle of rebuilding my HVAC box it became clear anything that can stop the heater core from being HOT 100% of the time, at least here in Arizona, is a good thing.

And in case anyone is interested, total cost was just over 13 bucks.
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So here is a summary of the situation:

1. OP's mod cost $13
2. OP's mod requires scheduled "maintenance" of opening the valves to circulate coolant
3. Jeep AC system, as designed/built, will cool the inside of the XJ perfectly well in Phoenix in the summer, provided system is up to snuff.

I think this is a modification with dubious benefit, and a PITA to remember to 'maintain'.
 
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#17 ·
There was a previous post where the breakage of the factory valve was discussed and the potential problem it could cause if you are on the trail. I had mentioned installing ball valves could eliminate the failure prone plastic factory part if it was important to you. The YJ's with 4.0 engine do not have the water control valve, the hoses run straight to the heater core and back. Since not everyone has engineering experience who is wheeling jeeps, it is an area where people might decide to get creative. As long as it doesn't create a hazard, its part of making the jeep personal.
 
Discussion starter · #18 ·
"dubious benefit"

Question "dubious". Huge benefit? No. Of course not. Some benefit? Yes.

"OP's mod requires"

What maintenance, nothing is required and even if I was going to mess with periodically opening and closing the valves, opening and closing a ball valve is a PITA?


"will cool the inside of the XJ perfectly well in Phoenix in the summer"

And now mine will do just a little bit better given I don't have to over come the heater in the HVAC box negative impact on cooling.

Please feel free to not do this to your vehicle however.
 
Discussion starter · #19 ·
Just wondering if those folks with the older style heater flow shutoff valves, the one for which the picture was posted, when summer hit, how often did you maintain the lack of flow through your heater core? Every few weeks open up the heater to refresh the coolant in the middle of summer?

Or did the heater stay off from late spring until some time in fall and then rot out regularly cause you didn't open up the valve every few weeks?

What, it didn't rot?

Imagine.
 
#20 ·
jsmiddleton4 said:
And now mine will do just a little bit better given I don't have to over come the heater in the HVAC box negative impact on cooling.

Please feel free to not do this to your vehicle however.
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I am not disagreeing that theoretically, the HVAC system might work a bit better. I just wonder if you will really be able to measure a difference, or if the improvement will be psychological.

I have been following your heater box rebuild efforts in anticipation of overhauling your HVAC system with great interest, since those of us here in PHX are VERY dependent on good AC. Your work there is well-planned.

I just happen to think that the shut-off valves are not likely to provide any SUBSTANTIAL benefit. I figure if they were beneficial, Jeep would have left the heater valve in when they did the body refresh in 1997, since the old design already had them in place. I suspect they removed it as a cost savings coupled with the knowledge that the HVAC system worked just fine without it.
 
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