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What I learned about my radiator flush and clean


NAXJA Forum User
This is a pretty messy job. It also takes a lot longer than you think if you are going to do it right. Don't let the online videos fool you....if it hasn't been done in a long time - or you don't know when it was last done you can plan several hours. This is mainly due to the cleaning cycles which require the system to cool.

What prompted me to do it was weak heat. I have full-fire heat now.

First, I drained the system. I didn't use the drain valve....was afraid it would snap and it's also a pain to access. I pulled the bottom hose from the radiator. Get yourself some hose clamp pliers to get the rings off...you probably will be doing it a lot on this job. Also, I accessed the hose by taking out my air intake housing.

To get it to drain liberally take off the hose connecting the thermostat housing to the heater core. Remove the hose at the thermostat housing. There's no need to take the hoses off the heater core side...avoid breaking those connections.

Get a WIDE pan. A 5 gallon bucket is no use. I mean...you want a 5 gallong bucket as well...but that that's to dump the pan into it.

Once drained, spray water through the heater core. Attach a length of hose like ChrisFix shows on youtube and drain it straight into a bucket. Go both ways. Don't force the water too much.

I wasn't sure if I needed a thermostat to fix the heat issue...but for $10 plus a gasket, it was cheap insurance. I installed an OEM 195' thermostat before my flush cleaner. The manufacturer of my flush cleaner recommended leaving in the thermostat to help build pressure which improves the cleaning performance.

For my flush cleaner I used Thoroflush from IronTite. It's a little pricey at about $20...but hey...this job is taking you some time so don't get cheap on the consumables. My sense was it did a pretty darn good job...more about that in a minute. Follow the directions on the Thoroflush. They say 12 minutes after the engine gets to temp. I called them and they explained why....and you should heed this time limit with the aging Cherokees for sure. Don't drive around with this stuff in your system.

Let the engine cool. The heater core hoses should be comfortable to touch. Use your judgement and don't be dumb.

Pull the lower hose and drain it. I pushed additional water through the heater core hose and let it drain out. Lots more discolored fluid was coming out.

I removed my coolant reservoir and cleaned it...I was shocked at the gunk in there!

I filled the radiator with water. Needed to start the vehicle to get the water to suck in so I could fill completely. Ran it up to temp. Let it cool and drained it. I did this 5 times! That was a pain. The water was gradually getting cleaner...and my heat was definitely back. I never thought it would take so many cycles.

I filled the radiator with my antifreeze first (since there was ample water in the system that didn't drain out) and then water . All done.

Heat blowing hot like you want.
Great walk though of the process!

This is almost identical to what finally fixed my overheating issues about 4 years ago. I believe this should be at the top of the to do list for every XJ. So many, threads about over heating issues, even after replacing every component, but they fail to really pay attention to the fuid and flushing the crud built up over 150k+ miles.
When I did mine a few years back, I was surprised at how much "mud" came out. I didn't have any heat or overheat problems except those due to a cracked radiator. My coolant now maintains it's green color.
Good writeup, especially the part about switching the flow back and forth on the heater core. Just when I thought it was clean, swapping directions would get another surge of brown crude. I would also add that if it's a Renix to eliminate the heater control valve. Assuming the plastic didn't crumble as soon as you touched it, it is very failure prone and helps cause the heater core to plug up. Make sure the surge tank and cap are good - the cheap replacements are failure prone too, btw. I think ecomike had a suggested replacement from a Volvo that was more durable.