Why does my 1998XJ have a 1996 heater control valve. I thought they stoped using them in 1996 I am puzzled

Got a picture? You're talking about the vacuum actuated valve that bypasses the heater core right?

Maybe some PO thought it should be there and added it?

If'n it were me, I'd yank that out of there without a second thought.

Would the 98 even have a vac line to connect to it?

Yes it is vacuum controlled. Looks all factory to me. I will remove and plumb straight to firewall since it blew apart. Just totally baffled why it’s there on this year model what other surprises are I am in for

It may have been sold at some point without an engine, or needed a rebuild, and all the PO had access to at the time was an older XJ, so they used it as a donor. They may have been unaware the heater control valve was deleted for 97-01, or rather than buying new heater hoses, they left it as is, to save some money. Just a guess.

Delete it.

I have a 96 and it has the heater control valve. I have the pipes to replace the valve with the 97+ system but I have hesitated. I've seemed to notice a bunch of 97+ XJ's having to have their heater core replaced. Some with fewer miles than my XJ has,(197k). I am curious as to whether or not the swap over by Jeep has anything to do with the 97+ systems I see failing. It worked fine the way it was forever then they changed it the last 5 years. Why?

The odd part is that it apparently has a vacuum line coming from the dash, which means the hvac controls are from a 96 as well?

No vacuum control sw on dash. Just the electrical rotary control.

The door selector lever on the 96 HVAC control is vacuum operated and needs the vacuum line. If you lose that vacuum line the default position is defroster only. Jeep uses that vinyl vacuum line (crap) that rots worse than rubber over time. Mine has cracked close to where it exits the firewall so I slid a rubber hose between it and the bypass valve. That's a good correlation between the presence of the bypass valve, and lack of one, to core failures. Food for thought.

I suspect the failures are due to lower quality parts rather than the design. By all logic and reason, the stagnant coolant all summer is worse for HC than the 97+ design.

I'll be entering my 3rd winter with the HCV deletion on my 95 (340k on the body and presumably the HC) and so far so good.

PatHenry, you seem to have the oldest XJ in this post closest to what I'm working with. I bought new hoses to yank the vacuum valve but found myself wondering... what if that vacuum line going into the dash is needed for something else? I have a 1991 Sport with close to 250k miles on it. The heat works great but under the hood is a mess. Good to know that the vacuum valve is supposed to be there and was not added by the same guy who installed the 2001 head on my 1991 block.
Can anyone provide a link to an existing post that provides a how too on removing this valve? OR... reply with a quick note on what to do with the vacuum line that comes out from the fire wall and plugs into the valve.
Also, on my 1991 currently the heater hose going into the HC is 3/4", the hose coming from the HC and returning coolant to the engine is 5/8". It looks like the 5/8" is what should be used on both in and out... anyone know for sure if the 3/4" hose is supposed to be there or should I have 5/8" on both?

Thanks!!

Yeah, it's literally as simple as pull the HCV and the 4 little hoses on it off, plug up the vacuum line and run the new hoses.

If you're looking to keep the vacuum line usable for something in the future, maybe find a coupling or something that matches the HCV, seal off the coupling and plug it into the original hose... maybe electrical tape to ensure it stays put.

I couldn't tell you on the hose sizes. I bought the 97+ hoses (they fit so nice it really does lok like it came that way) and they are spot on for the sizes.

I used a small screw (one with a built in washer) and some automotive sealer to seal off the vacuum line - then zip tied it along the fender to one of the wire harness sleeves.

That has worked beautifully for me for over 3 years now and my heat is still working nicely exactly as set on the controls.

I do think my blower motor may be on the way out, but that's completely unrelated... lolol.

[QUOTE=cspaltro;3627997Also, on my 1991 currently the heater hose going into the HC is 3/4", the hose coming from the HC and returning coolant to the engine is 5/8". It looks like the 5/8" is what should be used on both in and out... anyone know for sure if the 3/4" hose is supposed to be there or should I have 5/8" on both?
Thanks!![/QUOTE]

Yes they are different sizes at the heater core. Another reason why it's easier to just order the 97+ hoses as they have the right ends. Stretching 5/8 to fit is hard and you risk damaging the end of the heater core.

One 5/8" line, one 3/4" line. Easy.