Heater is weak

[willtodo]

Why would my heater be working poorly?
things I have tried
yes it has a good thermostat and engine is up to temp
I have flushed heater core to verify flow
the temp changes slightly when I adjust dial from cool to warm

[gary63]

do you have good air flow and can you hear the valve cycling opening and closing when you turn your temp. knob? the system works off vaccum so if you can't hear it you my have a leak.

[Mudderoy]

I noticed a problem with mine shortly after I started having issues with running hot on the highway. I didn't make the connection at the time. Fast forward 5 years later and replacing the heater core seems to have at least helped my running hot, or heat creep, on the highway.

If you've flushed it then it might just be full up with crap. I flushed mine right before changing it. A lot of stuff came out, but the problem wasn't resolved. Oh it did heat better after the flushing though.

[willtodo]

yes good air flow,, I question if the valve is fully switching over but it does go from cold to kinda warm

[4.3LXJ]

Those cores are easy to plug up because the passages are so small. And also hard to unclog. You probably need to replace the core

[Carves]

Probably should add the "blend door" to your list of possible issues.

[willtodo]

I look behind the glove box and I see the blend door that I think ur referring to,,, it seems that when its in max cool the door is shut,(recirculate) and in all other positions it blending fresh air,,, is this normal? it has the factory 190 degree thermostat ,, with ambient temp about 50 degrees and the temp gauge settles in at about 185,, could it be that the thermostat isn't opening completely and the flow isn't very good,, or does the water pass through to the core around the thermostat

[Mudderoy]

yes good air flow,, I question if the valve is fully switching over but it does go from cold to kinda warm

No valve in the 97+ Cherokees. I got excited when I read about the valve on the heater hose then found out they did away with them. I guess it's good since it's one less piece to go out, but that means hot water is flowing through the heater core most of the time.

[Carves]

Blend Door is in the gutz of the system.


http://i1143.photobucket.com/albums/n629/carves-oz/Vehicle%20Bits/BlendDoor_zps59880f83.jpg


IF ... its the issue ... I think theres a repair available for it - similiar to the Grand Cherokee.
Google ought to find it for you.

X 2 with Mudderoy on the constant coolant flow to the heater core.
No tap on the 97+ models ... and the heater core gets its flow from the bypass gallery in the thermostat housing - where the coolant temp sensor is located.


http://i1143.photobucket.com/albums/n629/carves-oz/Vehicle%20Bits/Sender10c.jpg

[Hopkins]

When you flushed it, did you try back flushing it? Anything clogging the system will be better removed by a back flush. Haha it's also a little cheaper than replacing the heater core, so it's worth a try

[willtodo]

ill try back flushing,,,, it seemed to work just a tad better this morning,, im going to get a fitting so I can just hook it up and turn the hose on and let her flow