Can you successfully bypass the heater valve?

[BIGSLVRXJ]

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

[AJPulley]

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?

[MoparManiac]

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.

[BIGSLVRXJ]

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?

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....
http://img.photobucket.com/albums/v316/jeepguy1990/Cooling%20System/Picture007.jpg
This is what I want...
http://img.photobucket.com/albums/v316/jeepguy1990/Cooling%20System/Picture003.jpg

[BIGSLVRXJ]

What kind of results has anyone else gotten from bypassing it?

[bajacalal]

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.

[AJPulley]

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.
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.

[BIGSLVRXJ]

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.

Do you think it'll effect the A/C performance a lot?

[cmotsvt]

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.

[sidriptide]

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.

[BIGSLVRXJ]

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.
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?

[jeepguy97]

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?

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.

[BIGSLVRXJ]

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.
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.

[NotMatt]

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.

[asatxj]

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.

[schmiedel]

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

[5-90]

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

[schmiedel]

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

[5-90]

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

[K2XJ]

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

[BIGSLVRXJ]

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
Just yank on it.

[vertigospiral88]

That's odd, if I turn both the fan and the "upper" slider knob (the one that chooses which mode the blower is on, ie defrost, etc.) to the off position it doesn't matter where I leave the temperature slider knob, it doesn't change the interior temperature at all.

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.

[uvaldetxj]

Okay...I just read this entire thread.

Yall are talking about the hoses that run from the firewall and the coolant bottle to the triple connector thing that goes to the front of the engine? If so, great... my plastic end on the valve snapped on me. I was thinking about just going to PNP and picking up as many connects as I could find. From what i've read though, it sounds like you guys are saying that the valve can be bypassed. Can anyone offer a clear picture? Please don't flame me, i'm a bit slow right now...Cuervo tends to do that.

[DeftwillP]

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

that pic isn't working Jon

[5-90]

that pic isn't working Jon

Bugger. I'll check it out between classes - it just didn't work for me either. I don't recall changing anything on that page yet...

5-90

[Rick Anderson]

You can get a new valve at NAPA for less than $15.
http://partimages.genpt.com/partimages/395130.jpg
http://www.napaonline.com/masterpages/NOLMaster.aspx?PageId=470&LineCode=BK&PartNumber=6601272&Description=Heater+Valve

If doesn't look at high quality as the OEM, but its better than a broken one.

[tchase]

Ok, I'll toss my 2 cents in on this one. Unfortuneately I don't have a definitive answer, but I'm looking into it. To the original poster, you say you've converted to the open system? If, in doing so you've eliminated the coolant tank at the firewall, you may be ok. You see, the previous owner had replaced the control valve with a couple tee's on my MJ. It's got heat but barely. In real cold weather if you start it and let the engine warm thoroughly before turning on the heat, you get decent heat at first but it then tapers off till it's just barely warm. Coolant temperature remains constant though. I'm thinking that with the tee's in the lines the coolant has two possible routes; through the heater core or through the coolant tank, guess which one offers less resistance? I don't think I'm getting enough flow through the core so I'm going to put the valve back in and see what that does for it. New valve is in the glove box now, hopefully I'll get it in in the next few days and let you know if it cures the problem.

[Rick Anderson]

You see, the previous owner had replaced the control valve with a couple tee's on my MJ. It's got heat but barely.
Its simple.

2 hoses to the heater core, one brings hot coolant to the heater core the other carries it away.

There is a valve spliced inbetween the 2 hoses, it redirects flow, either allows it to flow in and out of the heater core, like described above, OR it redirects the flow directly back to the motor, cutting out the heater core altogether.

If you going to eleminate the valve, then all you need to do is put in a hose from motor to the heater core connections on the firewall. Even if you get them backwards, I'm sure the heater core will still work fine running in reverse flow. OR just splice in straight barb pieces to connect the 2 hoses to make one, as you remove the valve.

No T's necessary, that is probably your problem, like you mentioned, the coolant has two directions to flow, and most of the coolant probably flows in the path of least resistance, which is probably wherever the T's takes it.

[tchase]

Its simple.

2 hoses to the heater core, one brings hot coolant to the heater core the other carries it away.

There is a valve spliced inbetween the 2 hoses, it redirects flow, either allows it to flow in and out of the heater core, like described above, OR it redirects the flow directly back to the motor, cutting out the heater core altogether.

If you going to eleminate the valve, then all you need to do is put in a hose from motor to the heater core connections on the firewall. Even if you get them backwards, I'm sure the heater core will still work fine running in reverse flow. OR just splice in straight barb pieces to connect the 2 hoses to make one, as you remove the valve.

No T's necessary, that is probably your problem, like you mentioned, the coolant has two directions to flow, and most of the coolant probably flows in the path of least resistance, which is probably wherever the T's takes it.

You have an open cooling system don't you? Just took a peek at my '91 and, for that set-up, you're right. No valve or tee's required. However on the older rigs like the original poster's '89 (in stock form at least) and my '88 the "bypass" is the coolant tank. Makes it kinda hard to get coolant in if you eliminate that.

[lawsoncl]

You can get a new valve at NAPA for less than $15.
http://partimages.genpt.com/partimages/395130.jpg
http://www.napaonline.com/masterpages/NOLMaster.aspx?PageId=470&LineCode=BK&PartNumber=6601272&Description=Heater+Valve

If doesn't look at high quality as the OEM, but its better than a broken one.


I converted my 89 to the open system because of overheating (the new cap on the new coolant bottle kept coming lose). I initially grabbed a heater valve from the pull-n-save, but it snapped in half installing it. Then I got a new one from Napa and it cracked and started leaking a week later. I said "screw-it" and just plumbed straight to the heater core. Works fine and I don't notice any additional heat in the summer. I don't have a/c so I tend to have the windows open when it gets hot outside anyway.

If you bypass the heater valve, you'll discover that one of heater core pipes is bigger than the other and it's difficult to get the smaller hose on. I heated the hose with a hair dryer and hammered an appropriately sized socket into the end to stretch the hose just enough to fit onto the heater core pipe.

[churky89]

If you are running the closed system you should be able to run heater hoses from the water pump and the t stat directly...same for the open system.
I had a rad hose leaking at one time,found a heater hose at AutoZone that had a 180 deg turn....stuck one end on the tstat and one end on the on the water pump....ran that way for some time....no hoses goin to the heater core.
The closed system is a hose night mare...where as the open has ...
1 hose coming out of the t stat..to the heater valve
1 hose coming out of the water pump..to the heater valve
heater valve has..
2 hoses going to the heater core.......