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bypassing underhood heater control valve

R

RenegadeT

NAXJA Forum User
Location
GSO, NC
I cracked this plastic valve that fits between the engine heater lines and heater core, some kind of heater control valve, on the passenger side engine bay. It has a vacuum line to it, coming from the cabin, I assume from the heater controls. Since I don't need heat right now, I plugged both heater lines and vacuum line and called it good.

Looking forward to the chilly weather, what would happen if I just connected the 2 engine coolant lines directly to the heater core, eliminating this line from the system? If I were to do that now, would hot air always be entering the cab?

1995 4.0L auto 4x4
 
You can do it, in fact I ran winterfest with it connected like that, since I couldn't figure out the HO heater valve install in my renix.

You will not have hot air all the time, as the blend door controls that.
You will have coolant in the heater core circulating at all times, so if the core starts leaking you can't turn it off.

You can use two 5/8 hose splices and just clamp it up and you'll have heat. I don't recommend running like that forever, but in a pinch you can do it just fine.
 
Lots of people have reported bypassing that valve and NOT getting cooked in the cabin.

I am going to try it at the next coolant change.
 
I eliminated mine earlier in the winter. Go to autozone and buy 3 feet each of 5/8" and 3/4" Goodyear hose, and run them to the heater core lines. 3 feet is actually too long but it gives you enough slack to run down the valve cover and take a couple of sharp turns.

The blend door setup has it so that air blows behind and through the heater core when Heat is selected, and blows in front of the heater core when Cold is selected. So you won't always have hot air but it will be warmer and the A/C will have to work harder
 
I ran my XJ with the hoses connected directly to the heater core for more than a year. I had no poblem with heat in the winter nor with the AC getting cold in the summer.
 
My 90 XJ has been swapped to open cooling and heater valve bypassed for at least 2 years, straight in to the core and back out. Works so well (for me) I just finished doing the same thing on the 88 MJ...and eliminated 6 more places for coolant to leak from.
 
i too converted a closed 90 xj to open with bypassed heater core.... it is much simplier under the hood, which is important to me. it also brings the truck up to temp quicker, it seems. the heater/defroster DEFINATELY gets warm quicker than before... i noticed that for sure.
 
thanks peeps, I'll keep this in mind. This is my $500 XJ, I'm not gonna put a $30 valve into it unless really necessary. The A/C in this thing doesnt work (no freon or condensor), so its not gonna work any harder without this valve ;)
 
IIRC that valve closes only when AC is selected, and it does sometimes stick in that position leaving you with no heat come fall. Therefore, we are probably all running around with hot water running through the heater core anyway. I bypassed 2 of mine with no issue.
 
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