I have a 99 xj with the 4.0l. I replaced the head with a reman unit. While dnoing the head I replaced radiator, waterpump, thermostat, temp sensor. I have flushed and back flushed multiple times. Still no heat. I checked the controls for all are functioning properly. She runs around 195 degrees no matter the conditions. At operating temp im not feeling much pressure on upper radiator hose. I back flushed the heater core again last night and she was putting out good heat for about 20 minutes then got even colder than normal. Im about to replace the heater core just hopeing there is another option.

 

Did you flush and backflush the heater core itself?
If it's flowing good with a garden hose through the core I wouldn't replace the core.
Maybe an airlock?
Disconnect a hose while running and see if it's flowing.

 

I have flushed just the heater core. I get good flow with a garden hose both ways. I think I have tried everything but I am at my wits end and afraid I am just thinking too hard.

 

What controls?

Did you climb in the passenger footwell and check to see if the Blend-Air Door actuator is turning the door intermediate shaft (white gizzy) when you run the temp control full red then full blue.

 

Yes sorry there was supposed to be an HVAC in there. The blend door motor and blend door itself are functioning properly.

 

What did you do to determine the Blend-Air Door is functioning properly? Remove the actuator and intermediate drive shaft and examine the drives and see if the door turns freely?

 

are both heater hoses hot when up to temp?

 

Yes I checked it then unbolted and tested motor and the door. Both operate normally. Last night before I left the shop I pulled it in and backflushed it. The heat worked good for 20 min or so then went cold again. I just went out and checked the bottom hose from the heater core. There was no coolant present. It was at operating temp last night the upper hose was almost to hot to grab the lower was pretty hot. Thanks guys for your input and help. Just lost and as this is how I transport my 2yr old im needing heat bad.