Did a radiator flush

Well I did a radiator flush on my '96 4.0 XJ 70k miles. Here's what I did...

I used a Wynn's 100% fluid exchange machine (in through the radiator, out through the block), and flushed 10 gallons of water through the system. Then I dumped a bottle of Prestone's 7 hour flush and drove around for a couple of hours.

I flushed it again with 8 gallons water, and then replaced the upper and lower radiator hoses, the thermostat, thermostat housing, and the radiator cap itself. I also removed and cleaned out the recovery bottle. There was about an inch of green sludge on the bottom.

Then I filled the machine up with 5 gallons of Prestone's 50/50 mix antifreeze prediluted with distilled water, and ran that through the system. I still need to adjust my freeze protection a little bit, but so far everything seems to be OK.

After the first initial flush (running water and the cleaner), I immediately noticed the Jeep was running between 10 and 20 degrees cooler, depending on driving conditions.

Now that I have antifreeze back in there, it's still running between 10 and 20 degrees cooler. Almost a little too cool... sometimes the gauge will be just over the white mark between 100 and 210. However when it's left idling, after 5 to 10 minutes, the temp will slowly creep up to where the aux fan will kick on.

Now weren't there some bare bones Cherokees offered without an aux fan? Meaning the cooling system should be efficient enough to keep the temp in normal range without the aux fan's usage?

My fan clutch seems to be nice and tight. Fan stops spinning almost immediately.

Actually sounds pretty good. What thermostat did you use, OEM and did you put the little bleed hole on the thermostat flange in the 12 O'Clock position ?
Keep an eye on the overlfow bottle, if you still have any air in there even from using the machine it could suck the fluid out in which case it will be sucking air in after that. When I do it I fill the overflow bottle to the hot position while it's cold. Did you leave the heater on in the hot postion when you were running the flush ? So that the heater core was also flushed ?

Air? Ain't no air for me when I fill through the upper radiator hose removed from the engine with vehicle parked level. Hold the hose up and pour it in with the cap off the pressure tank until the coolant reaches the full line.

I seriously doubt over-the-counter flushing will remove enough lime/scale buildup to restore factory cooling capacity but if it does, more power to you. A new rad isn't much money when compared to a new engine. After years of Voodoo repairs to my '89 cooling system new rad was the real mojo bone.

I had the heater on it's highest setting. I used an OEM thermostat and the hole was mounted in the 12 oclock position. I assume it's a 195 degree thermostat (factory).

My operating temp seems to be about 180 right now. Sometimes it'll climb up to 195 but not often. Isn't this a little too cold? Why isn't it heating up all the way?

I don't think it has anything to do with the new thermostat. These temps started as soon as I got the old coolant out of there. I ran it with water and Prestone flush for a few hours. It never really got over 180ish. This was before I replaced the thermostat and housing.

The sensor that screws into the thermostat housing doesnt need to be screwed in only to a certain depth does it? I just tighted it down upon reinstallation. Could that be why my gauge is reading a little low?

I think I'd chalk it up to gauge inaccuracies, unless you notice a big dip in milages I'd leave it alone. If milage dips then it's not coming out of cold loop and is in fact running too cold. The other thing is if you still have air trapped in there then the sensor is not reading coolant but rather the air around it trapped in there, happens on the 97+ with the sensor in the tstat housing and have heard of it happening on 4.2YJ's with the sensor in the back of the head. The best way to top of a rear mounted sensor is to top the coolant off with the nose facing downhill and top it off thru the sensor hole. Others fill it thru the upper hose.

RichP said:

The best way to top of a rear mounted sensor is to top the coolant off with the nose facing downhill and top it off thru the sensor hole. Others fill it thru the upper hose.

Click to expand...

Another way is to point the nose of the Jeep facing uphill and top up the cooling system through the t'stat housing and the upper radiator hose. A bubble of air will remain in the hose since it's at the highest point in the system but after running the engine with the heater turned on full, that air will eventually get "burped" out. When you shut the engine off and it cools down, it'll draw coolant back from the expansion reservoir into the radiator as the cooling system depressurizes. Therefore, you'll need to make sure that there's enough coolant in the reservoir so that you don't get air drawn back into the radiator instead.