I have an NBS XJ which doesn't have the cutoff valve. I know the change over was a blend door for the NBS, but I'd like that little bit of extra cool (today was equivalent of 97* and crazy humid). I also left out a plastic piece in the evap/heater core box as it wouldn't stay in place. I'm not sure if it has any effect, but maybe peace of mind.

Id like to do something like this;




I don't know which hose, where to get the valve and other necessary parts needed, appreciate any input.

 

In that pic, The valve is a very common plumbing part called a ball valve. You can get one at any plumbing or hardware store. Cant really tell what size but probably 1/2 inch. I would imagine you could screw in a couple 1/2" barbed ends into each side of the ball valve and then push the hose on them and use hose clamps like in the pic.

 

You need 2. Put one in each heater hose that travels to and from the heater core.

 

I'd go 5/8" or maybe even 3/4". Half inch is too small.

 

X2

 

Make sure you use brass valves and fittings. This is no place for PVC.

 

Thanks a lot everyone!

Ball valve, got it! Ill stop by Homedepot today

I just did this, but now I can't remember, aren't the hoses two different sizes? If not, is it possible to have the hoses backwards?

 

i personally would run it so that when you have it closed that the one hose runs into the other to keep the flow if that makes sense

 

No, that's not right.

You want all the flow or heat conduction to stop. That's why I said to use two valves.

Otherwise there's no use in doing this.

 

i basically mean you would want to unhook the two hoses from the heater core and hook them together bypassing the heater core, that way the antifreeze flows through the system the way it should. If you just shut a valve off on both hoses then it won't flow through the rest of the system the way it should.

if you look at a 89 style cherokee it recirculates it through the overflow bottle and back to the other hose when the valve is closed

 

Even if you put a shutoff valve on the supply line close to the thermostat housing, the coolant in the hose will eventually pick up heat from the coolant in the thermostat housing. Heat transfer goes hot-to-cold, it can't be stopped without an insulation barrier, the cold coolant will wick heat from the hot coolant period. But the fan blowing over the heater core is also transferring heat, and by slowing down the fluid that enters the core you can prevent the heat from building up so high so fast. You can make it so the coolant in the heater core is always warm rather than hot. That's the best you can do. The stock valve always lets some coolant flow through the core, just at a reduced rate. An H-shaped bypass with a single shutoff to the core will do the same thing, it won't stop coolant in the core from heating up, but it will slow down the rate of transfer, so that it doesn't get so hot so fast.

 

Actually, the only way to ensure a cold heater core is to disconnect both hoses. Leave one open to the atmosphere and loop the other back to the engine.

Then when heating season comes, you have to put everything together and add back a quart or two of coolant.

However, maybe the OP's problem is actually an air conditioner that is not performing up to specs.

At 97* and high humidity, very few vehicles can maintain a cold cabin temperature in any case.

 

I think '97 and later Cherokees only have 2 heater hoses, a supply and return.

It doesn't have all the complicated plumbing earlier ones have, especially RENIXes.

The '97 and later temps are controlled by blend doors, like most modern vehicles are.

 

Right, the later models actually close off the core inside the dash, but the older models always have the core exposed to the airflow so you have to reduce the heat in the core to get lower cabin temps

 

Yeah, I remember reading that somewhere here. I think it may be 5/8 & 3/4, but I'm not sure. I have not had to mess with it yet myself.

I'm QUITE sure it's larger than 1/2".