My 98 stock heater hoses - 3/4" (supply - red) and 5/8" (return - blue).

98 Jeep OEM Parts manual - #1 - Supply hose, #6 - Return hose
94 - 96 OEM Parts manual - hose from valve to water pump (metal tube) as return hose

My hoses are the same size and orientation as in the diagram.

The water pumps metal tube has been known to become rusted and clogged where it threads into the water pump, restricting coolant flow. (The heater core should be flushed separately).

 

'96 and earlier have a heater water control valve. The only time it fully blocks flow is if the system is selected for Max A/C or OFF.

'97 and later always have hot water circulating through the core. They manage heat output by blend doors.

 

yes

 

Again, thanks for the assist everyone!

I only want to do this just for that additional bit of cool air. Every little bit helps in a climate that has the same temp as hell.
Another concern was that I left out that little plastic piece that goes in front of the heater core cause it would not stay in place. I was worried that it would cause excessive heat to build in the box.

The heater core and Evap is literally new 3 days ago. AC is freezing cold and heat works damned good (admittedly I still have to burp the system).
My XJ is an 01' so it indeed only has two the hoses, and it does not have the rust prone metal pipe. Thanks for that and sizes Muddz

 

If you want to really block all heat at the core, then do what Firestorm suggested and make an H-shaped bypass on the hoses and use two shutoff ball valves to isolate both sides of the core. Its overkill but it will do what you want

 

I think part of the problem, maybe a lot of it, is heat gain in the summer.

We have a lot of glass compared to the interior volume. And I don't think that the XJs are insulated nearly as well as modern design vehicles.

The OP might try deep tinting all the windows as far as his local laws will allow to cut down on solar gain.

That little plastic piece he left off might be allowing heater core heat into the cabin when it isn't wanted. Don't worry about the box being too hot.

I live in Arkansas, which is usually hotter than Florida and every bit as humid. We go to Florida for vacation and to cool off.

 

The old AMC Eagles had a vaccum-operated valve from the factory that operated this way. When you turned on the A/C it would divert the coolant flow away from the heater core.

 

Yeah but that's just one valve to prevent new coolant from entering the core, the return side of the core will still wick up heat (just not as fast as you are blowing it off).

There are a few different valves that will work for this if you are willing to use just one. Most of them are setup for 5/8 line, which is the egress side on my 91. That will also work, since new coolant can't enter while old coolant is in the core, but it will wick up heat pretty fast since it will be in full contact with the hot coolant.

 

I've been looking at valve(s) for a possible re-install of a Napa coolant filter. Originally installed to filter out excessive rust build-up from the cooling system.

It was installed in place of a backflush T fitting, on the supply hose to test it out. I was planning on re-installing to the return 5/8" hose (better size hose for the filter hose fittings.)

I'm not sure if a valve is needed? I was thinking of using straight valves or a three way valve.

The ones from the pics below are rated for higher (hot) water & fluid temperatures and psi. (rated for use with water, gas and oil)




.
3-Way - 1/2" and 3/4" threaded and sweat type. The pic is a L-Port, what's needed is a T-Port, to fit inline with the heater hose.





Ball valve with drain - 1/2" and 3/4" threaded (some are sweatable type) 1/2" drain valve works from both sides of the ball

 

Engine and road vibrations might cause sweat fittings to eventually fail.

There again, nothing lasts forever.

 

I suppose that's why clamp, push-lock, quick connect & compression fittings are used in automotive applications. Solder joints potentially become brittle and break. Not designed for routine maintenance.

We used mostly welded and threaded pipe fittings for larger vehicle and vessel applications. Fittings designed for around the home may or may not work for automotive.

RV's are using more plastic, over the years have used copper tube fittings and solder joints for their water supply.

Here are a few ball valves. A valve may not be necessary, would mostly help to re-direct coolant for a filter.

There are threaded hose nipples that fit 5/8 and 3/4 inch hoses.

http://www.supplyhouse.com/Ball-Valves-5000

 

I don't remember who it is, but there's a member who lives in Tuscon, which trumps both of you for heat by a wide margin.

He's jumped in on this kind of discussion in the past, and has eliminated his stock heater control valve. Just took it out. He sees no problem with unwanted heat in the summer.

I think it's much ado about nothing. If your blend door is working correctly, I don't think there's a problem worth solving.

Spend the time, effort, and money on window tinting or insulation in the roof, and you might see a worthwhile return on your investment.

 

Yes, Im actually leaning toward not doing anything. Seems everything is working fine and the initial worry is not coming to fruition.

 

Yeah, I've been in Phoenix, Tuscon, Las Vegas, Death Valley, etc. I've experienced temperatures as high as 116* out there. You know it's hot. But with 5-10% humidity, when you sweat you do get some relief.

But I've lived in the South all my life. We here in Arkansas can and do have temperatures well above 100 degrees for weeks at a time. The problem here is the high dewpoints. That means the air also has a lot of moisture. That means you are going to pour out sweat, but can't cool yourself. The heat index values can be 110-115 degrees for most of the day.

It's just miserable without strong air conditioning. People up in the Northeast start dying above 90 degrees. Their humidity is not as bad as ours. They might experience that only a few days out of the year, and not every year. It doesn't get below 90 sometimes at night around here.

It's almost October and we are still having highs of 95 degrees.