Heater problems

[McClare]

92 MJ, 4.0L

 

My Heater doesn't blow hot air like it should. It comes out lukewarm at best. The blower works fine. The door that opens when you slide the selector from cold to hot works fine. The thermostat has been replaced. The hoses going into and out of the heater core both feel the same temperature to the touch. The engine is not overheating and the temperature gauge sits roughly in the middle after it gets warmed up.

 

I'm running out of ideas here. Someone told me that maybe a coolant flush would work. I'm not really convinced but I've got nothing else to go with. Any ideas?

[ejndssn]

i have to get the OEM for my 89 cherokee which is the only one that works :hmm: the after market ones did not do well. it took me a while to figure this one out :dunno: but my mj has no problem with the aftermarket ones it is some times a crap shoot when getting them. i always test them by boiling hot water on the stove. what's the temp rating on the last one you have purchased and where did you get it from

[HOrnbrod]

92 MJ, 4.0L

 

My Heater doesn't blow hot air like it should. It comes out lukewarm at best. The blower works fine. The door that opens when you slide the selector from cold to hot works fine. The thermostat has been replaced. The hoses going into and out of the heater core both feel the same temperature to the touch. The engine is not overheating and the temperature gauge sits roughly in the middle after it gets warmed up.

 

I'm running out of ideas here. Someone told me that maybe a coolant flush would work. I'm not really convinced but I've got nothing else to go with. Any ideas?

 

First thing to do is disconnect the in and out hoses from your heater core at the right firewall, and flush out your core with a garden hose. The crap that comes out will amaze you if it's never been done. Reconnect the hoses and try it. If the heat output is still paltry, it's probably the water control valve. This thing operates on vacuum to open and close using your heater controls. Make sure that it opens fully when you turn the heat on. You can see the lever opening and closing the valve. It could be stuck partially open. If so, get rid of it. In 1997+ XJs Chrysler quit installing the water valves. After going through three of them in two years, I just got rid of it by purchasing new 1997 XJ supply and return heater hoses, and all is well. Oh, and block off the old vacuum line too. This allows water to flow constantly through the heater core keeping it clear, and adds a bit more liquid for overall engine cooling. The heater flapper door stays shut until you activate the heat, and there was no more heat in the cab during the summer as before. Just one less thing to go wrong.............

[McClare]

to flush the heater core do i need to drain all the coolant out of the lines first or will only a little bit spill out when i disconnect the lines to the core?

[HOrnbrod]

Coolant will drain out from points higher when you disconnect the heater core hose connection. I do a complete flush once a year, and now is the time, fall season. I don't like using caustic chemical flushes, they are not needed if you flush the cooling system annualy, IMHO. Disco the hoses, and flush front and back, rad, heater core, and engine.