dave1123

Why is it my heater in my 2000 XJ works so much better than the one in my 2000 WJ? Both systems are clean and the heater core in the WJ is new, both work well, it's just the one in my XJ is like a sauna whereas the one in my WJ gets hot, but not as quickly or as hot. My son made the suggestion that the air volume in the XJ's cabin is smaller than the WJ, but IDK if that's all of it. The WJ has always worked this way, it's just that I'm amazed how hot it gets in the XJ. Is the core or blower larger?

jordan96xj

It's a good question, considering how similar things are (based on your details). My first thought would be to take an IR gun to the input port of the heater core on each vehicle and just see if the coolant going in is generally about the same. That way I would know that the difference is before/after that point. It wouldn't answer the question by itself, but it would lead my curiosity to the right area.

My initial guess, given that everything else was in proper working order, would be that perhaps a difference in the airbox and mixer design might be the explanation. For example, perhaps the XJ box is more basic and there is a more direct path for the heated air, so you feel it more directly off of the core, vs. a more complicated design where the air has to route a little longer and loses some of its heat before being felt at the vents. This guess is just based on the fact that the XJ vents are so close to the airbox, where as the grand has a little more dash complexity to contend with.

Also, something as simple as a blend door that is not closing all the way (or isn't sealing very well and allowing too much air past) could explain a difference, where some cool air is being mixed with the heated.

dave1123

I got to thinking there is something else involved here. My A/C in the WJ only worked for a week after I got it in 2012. I recharged it with dye in it and it still was dead in a week, showing no dye anywhere so I assumed it was the evaporator. I put the repair on the back burner and drove it without the A/C for 4 years until the heater core started leaking. At that time, I barely had enough money to fix the heater so the evap had to not be replaced. The new heater core started leaking the next day, so the dash had to be ripped out again! My mechanic replaced all the foam seals when he did the heater core, so that's not the problem, HOWEVER I've always had a leak of hot air coming from under the dash and it's NOT coming out of the heat ducts. It seems to be coming from behind the heater box and I've looked for any openings around any thru-firewall stuff and can't find it. SO, that heat leak may be cold air in the winter. The only place I haven't checked is behind the brake booster although if you put your hand over the heater outlet by the driver's feet, you get no air, but closer to the firewall, you can feel a breeze when the engine rad fan is running. People on the passenger's side don't feel it either. WTF?

jordan96xj

I'm afraid I don't know the WJ airbox/dash arrangement at all. So I couldn't even guess where the likely opportunities for cold air entering (or mixing) would be. One of the biggest pass throughs from the engine compartment is the blower fan itself. Has that been double checked to ensure it isn't pulling outside air into the mix when it shouldn't be? It has a gasket that helps seal it against the firewall to keep out moisture and air.

If there was a big enough hole in the firewall that you could feel a breeze on your hand when the engine fan is turning, I would think that would be a pretty sizable entry (easy to spot). Does the inside of the Jeep get fumes like air is coming in from the engine compartment? normally when there is a firewall leak like this you can smell that burning oil/gas smell pretty strongly.

PatHenry

It's gotta be that draft allowing cold air in.
My XJ is hot, but it's not any hotter than my Corolla (which has a tiny engine, a huge dash and rear seat heat vents in the floor). If anything, I'd say the Corolla is warmer than the XJ, as I expect it would be since it's much newer, has much lower mileage and the cabin is quite a bit more insulated.
My buddy has had several old GC's and as far as I can recall the heat was always good.