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Can you successfully bypass the heater valve?

BIGSLVRXJ

BIGSLVRXJ

NAXJA Forum User
Location
Des Moines, Iowa
On 97+ XJs, there is no heater valve. What did they change inside the dash to accomodate for this? Could it be done to an older XJ? I would like to have just the two simple heater lines running to the core. So am I just a dreamer or could it be done? Much obliged for any insight to this.
Collin
 
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Older xjs have a heater door, and use a "bypass" to help, only it isn't a bypass- just a blockage. Later model xjs have a bypass that helps to reduce heat in the heater core for A/C purposes, or so I believe. I can't verify the heater door, or lack thereof, in later models.

Can you reword your question? I'm not sure what your asking- what do you have and what do you want to do?
 
When my father and I were changing the heater hoses we snapped one of the plastic ends off of the heater valve. We figured, screw it, just bypass it completely since it's winter anyways. The lever on the heat controls works the door i think? So i can still blow air out of the vents that is outside temp, but the heat still works when i move it to warm. I'm not entirely sure if this will affect the A/C in the summer, but seeing as how mine isnt working right now anyways, I don't really care.
 
ajpulley said:
Older xjs have a heater door, and use a "bypass" to help, only it isn't a bypass- just a blockage. Later model xjs have a bypass that helps to reduce heat in the heater core for A/C purposes, or so I believe. I can't verify the heater door, or lack thereof, in later models.

Can you reword your question? I'm not sure what your asking- what do you have and what do you want to do?
Click to expand...

Okay I've got a 90 XJ but I've converted it to the open system. So I have 2 hoses coming into the valve and then two going to the heater core from the valve. I want to make it so I still have functional heat and air conditioning(I know heat won't be a problem) but I want to do away with the heater valve. Sorry about the unclear wording at first.
This is what I've got....
Picture007.jpg

This is what I want...
Picture003.jpg
 
What kind of results has anyone else gotten from bypassing it?
 
I bypassed mine one night because the heater valve came apart from age. I just un-hooked the heater core, let it run dry and routed the hose from the water pump to the other heater fitting on the thermostat housing. The hose had a kink and I wouldn't recommend or see any reason to bypass the heater core or valve except only as a temporary solution to a coolant leak.
 
BigBlackHeep said:
I want to make it so I still have functional heat and air conditioning(I know heat won't be a problem) but I want to do away with the heater valve. Sorry about the unclear wording at first.
Click to expand...
Oh, ok. Just remove it and do what was done for years... run the hoses directly to the core. When the valve is in the bypass position, it just returns the coolant to the engine. Old engines had the cooant flowing through the heater core all the time. Your A/C might not be as efficient, but it's simple.
 
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ajpulley said:
Oh, ok. Just remove it and do what was done for years... run the hoses directly to the core. When the valve is in the bypass position, it just returns the coolant to the engine. Old engines had the cooant flowing through the heater core all the time. Your A/C might not be as efficient, but it's simple.
Click to expand...

Do you think it'll effect the A/C performance a lot?
 
I doubt there will be a problem in losing the valve, I plan on losing it when I get around to converting to the open system. As someone pointed out most older vehicles had hot water going through the heater core all the time.
 
i converted my 90 to the newer system, i just cut the extra tubes off the valve so it is simply a single tube with a valve in the middle. put it back in to cut down on the amount of in-cabin heat in the summer time. even without the blower it will give off alot of heat especially wheeling at low speeds with higher RPM and engine temps.
 
sidriptide said:
i converted my 90 to the newer system, i just cut the extra tubes off the valve so it is simply a single tube with a valve in the middle. put it back in to cut down on the amount of in-cabin heat in the summer time. even without the blower it will give off alot of heat especially wheeling at low speeds with higher RPM and engine temps.
Click to expand...
So it probably wont cut down on A/C performance, it will just radiate more heat in from the core? Am I understanding that right?
 
BigBlackHeep said:
So it probably wont cut down on A/C performance, it will just radiate more heat in from the core? Am I understanding that right?
Click to expand...

If its radiating more heat its gonna cut down on A/C performance. Try it without the valve, if its not cool enough cut off the ends and reatach it in line.
 
jeepguy97 said:
If its radiating more heat its gonna cut down on A/C performance. Try it without the valve, if its not cool enough cut off the ends and reatach it in line.
Click to expand...
Well since it's not summer I really can't try it but I suppose I'll give that a shot in the summer. I just figure its one less place to leak from. Thanks for all the help and suggestions guys. If anyone else has ideas/thoughts on this I'm still open.
 
Personally I wouldn't remove the valve. If you want to see what it will be like with coolant running through the heater core ALL the time, just leave the selector all the way to the right (hot). Even with the fan off, it still heats the cabin up and can get VERY annoyingly hot in the spring, let alone a sweltering hot summer.

I had a short period of time where I had to leave my selector in hot or else the severly aged and cracked valve would leak coolant all over the place, and it wasn't very much fun driving around with the "heat" on all the time.

Just get a new valve to replace the old, brittle one... and be done with it.

I'm not sure how the newer XJ's are, but I'm guessing that they use some other type of method for controlling heater core flow (maybe the valve is under the dash?), because I doubt the system is constantly flowing water through that heater core... doesn't make any sense to have the heater core fighting against the A/C in the summer.
 
I have the valve in place on my 91. It doesn't work as for some reason the vacuum line has no vacuum. I haven't found where it goes after it goes into the heater core area so I can't fix it. It's open- letting coolant to the heater- all the time and it's not hot all summer. I wired it closed for a week just to test it and didn't notice a difference. I replaced it a while back and this summer I'm going to pull it if I can't fix it and put the hoses from my 97 on it since it doesn't make much difference.
 
If it helps, my 1988 XJ (with the 4.0 FI engine) has no vacuum control valve (it must have been taken off somewhen). In winter it's no problem at all, but now it's getting warmer I feel the AC is not always cold enough, and if I use my XJ with normal ventilation (no heating nor AC), I sometimes feel the air somewhat warm, not really too much but sometimes it's kind of annoying as I don't like using the AC at 9.00PM because I get warm air from my vents. Also if I put my hand under the dash, some parts feel a little bit warmer than usual (the heater core is always receiving coolant). I'm definitely putting a new heater valve in...

I had some doubts, but the pictures I see resolve all my problems but one: I see the valve has 4 5/8 connectors and a vacuum line, I also see a white vacuum line which is disconnected on my XJ, so that's good and bad news. I just don't know how to test this line out, what controls this vacuum line? How can I test if it works and what do I have to put apart to see where it comes from in case it's not working properly?

Regards
 
I eliminated mine entirely when I did the copper heater lines (there's a pic on my website,) and I haven't noted any ill effects.

The closest thing to "plastic" that should be in any cooling system is the rubber hoses - everything else should be brass or copper (or cast iron or cast aluminum.) I know plastic is cheaper; but, dammit, it just don't last too good.

1988XJ/4.0/BA-10/NP231/D30-35/3.07, in case you were wondering.

5-90
 
Well, I ordered a heater valve today, no plastic at all, but it isn't the OEM valve, I saw it and it seems quite cheap... In my case I only notice ill efects if I use the XJ and then leave it for one or two hours, if I then resume driving it feels quite hot inside, and that wasn't a problem before I connected the heater core (I had it disconnected), so it must be due to the heat that's dissipated from the heater core when the truck is parked, and it only goes away if I turn on the AC, which I don't really like too much as I drive a lot of short distances (at most 5 miles per drive, like 4 times a day).

Regards

Regards
 
Makes sense - turn the vent fan on when you get in, and that should solve the issue. Come to think of it, I've noticed an increase in sitting temperatures - but since I always have the vent fan on (rain, snow, $4!7, or mud,) it ain't around for long. I'm just a fresh air fiend (which is odd, because I've been in California for 15 years. Isn't the general attitude out here something like "I don't trust air I can't see?")

Since I don't have air conditioning, I can't say how its performance is affected by running coolant through the heater core all the time. I need to correct that problem, though...

5-90
 
Speaking of heater control valve...i will be replacing mine this weekend. I havent taken a close look at it but how do you remove the vac. line from the valve?? I would like to know if there is anything special to do or just yank on it??

Cheers
 
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