89cherokeedave

Hello, i want to flush the heater core in my 89, but need to know if the heater control valve needs to be removed or if I can just disconnect the hoses at heater box and flush it that way?

sgtskid

The way i have always done it is to buy some radiator flush from autozone and then disconnect the hose running to the top of the thermostat housing. turn the engine on with heater on high and then plug a garden hose into the open end of the hose. This will pump water through the engine and the heater core. I do this until the water flows clear I then shut the engine off pour the flush in top of with water and let run. Drain it and repeat as necessary.

89cherokeedave

I could try that, I just wondered if on the earlier renix jeeps, it was different because of the heater control valve. Would like to just flush the heater core, but didn't know how well it would do with that valve assembly in place?

thundaluvin

I just did mine. disconnect the heater hoses at the heater core, Use an old heater hose or buy a new length(i keep a new length on hand at all times), drain the heater core with an air compressor, pour CLR into heater core, wait 10 minutes. then flush backwards. repeat process if you get alot of gunk out. when flushing it use water and repeat until clean water comes out. IT does wonders for your heat.

89cherokeedave

That is the info I was looking for,, on the heater core is the top opening the inlet for coolant to come in, or is it the bottom one?

tjwalker

When you flush the heater core, flush BOTH ways through both inlet and outlet, and take your time.

I like the CLR technique for particularly clogged cores. As the next step if it doesn't work is replacement of the core, you have nothing to lose here. Here is a link.