Then the blend door very well could be the problem then. Wonder what happened to those days when humans were smarter than their car and heaters only had two settings... On and Off. Too many things to break now because we are just flat lazy. lol

 

I'd look at the blend door. I had a problem with the temperature slider sliding over to heat but it wasn't moving the door properly.

 

I did just the opposite. I added system flush and ran it for a bit before draining. When I was swapping my radiator I flushed the radiator really well before I put it in. I pulled it from my 99 and into my 98. Then I flushed the motor with the garden hose several times. I only pulled one heater hose during this. I didn't flush just the core.

I then proceeded to install new pump, t-stat and housing, metal heater hose tube, and upper and lower radiator hose. The heater hoses were not in stock locally so I didn't do them. I still didn't have much heat. It was warm enough to melt ice from the windshield over about 30 minutes but didn't change the air temp inside the Jeep. I was thinking it was the blend door because the **** doesn't move all the way to hot. But if I move the lever that the cable is connected to I can hear it closing tightly.

Once the engine is warmed if I leave the blower off then when I first turn it on it's hot and about 5 seconds in it then turns barely warm. So long story short I guess I should have and still should flush just the core.

 

Dang raslfrasl double post!

 

"System flush" lol I want to share something from the past that I do not recommend but does indeed work. First make up your mind that you are going to replace all the hoses on the system. Then pour about a half cup of muratic acid in the system and run it for about 5 minutes and then flush again. Then replace all the hoses. The results are absolute bare metal on every surface in the cooling system. lol

 

+1 This will probably work, but it is super risky. Flushing the entire system like this would be better utilized as a last resort to remedy overheating issues. It will take years off of the cooling components and possibly destroy gaskets. If you tried this in a porsche you could easily total the vehicle...


In my opinion the evidence points to corrosion in the heater core. It could also be that the heater core fins are dirty or corroded, which would insulate it and keep it from transferring heat.

If you are going to flush it with acid I would recommend isolating the heater core. If you disconnect it from everything then just about any acid will do the job (hydrafluoric, oxalic, sulferic)

You could try disconnecting the heater core hoses, plug one end, then fill up the heater core with a 25% acid and 75% water solution (depending on the acid). Make sure you wear gloves and and take safety measures. Let that sit for 5-10 minutes, then flush the heater core in both directions. If it is corroded and pitted bad enough on the interior this could cause a leak in the heater core, but that would really only be exposing a problem that already exists.

After it is flushed well make sure it is quickly reconnected with 50/50 antifreeze to keep it from oxidizing.

Or you could take out the dash and replace the heater core.

 

I have a feeling white vinegar would work. Maybe it would need to sit in the core longer but is a bit safer at least. I use it a lot to clean stuff at work. Mostly hard water deposits and corrosion. Usually I use 5% but it is sold up to 10%. I've actually had metal, plastic and rubber pieces full dissolve by leaving stuff in it too long accidentally. It would take like 12 hours or more to do that though. I think maybe an hour or so soaking with straight 5% vinegar would do some good before flushing. I just might have to experiment with that.

 

New heater core is only like $40. Why bother cleaning?

 

When you're at operating temperature, have you tried turning the heat all the way up and selecting "VENT"? Mine blows crazy hot air this way and I thought it might be a backdoor way to get heat until you can figure out your issue.

 

Just an .02

On the surface this statement is easy to agree with. I applied that thinking to mine a couple years ago. Unfortunately, the gain in heat output was marginal at best. Changing the core is an annoying job and was not worth the effort. For my application, cleaning would probably have been a wiser choice.

 

That's why I don't recommend doing it anymore. Muratic is too strong and aggressive. Just sharing a historical operation that did work but had to be handled with care. Vinegar would be much better.

 

Fast forward to yesterday. 28 degrees, snowing.
Jeep running at 207 degrees according to my scan tool. Heat barely warm enough to melt the snow on the windshield. Looks like Ken R is gonna have to replace the blend door!

 

Today I took the stepper motor/blend door--actuator off the heater plenum today. I tested the actuator motor, it works fine. I turned the blend door by hand and it flips to full hot and is solid when the door reaches the HOT position. Flipping it the other way to the full "Cold" position, it does not feel solid, like at full hot. The air at full cold is exactly that, full cold. The air at full hot is kinda warm, not even close to hot. Tomorrow I guess I will cut into the heater box plenum by the blend door and see if the door is broken or off it's axis.
The fun never ends!

 

did you ever figure it out? I have same issue in my 98xj. Did everything you mentioned even blend door. Still luke warm at best.

 

Matt98,
When you did your blend door, what did you do and how was the door?