back to my cooling problem...

Well here I am trying to figure out the same problem I had before. 89 cherokee 3 row radiator, new water pump, thermostat and intrepid bottle. I am overheating slowly if im idle or driving at slow traffic jam speeds. I narrowed it down to poor coolant flow in my heater core as my heat is luke warm and not real strong from vents. I tried unclogging my heater core with a hose and as I poured water in it came trickling out the other. I was never able to unclog it basically. Is there something I can mix in my coolant to help unclog or do I have to just replace the damn thing.
thanks!

Maybe try a can of the Prestone 7-Day Flush.

With regards to the blocked core aspect, Ive heard of people use white vinegar left overnight with good results. Ive also heard of a guy using high pressure to blast the crud out if you get desperate, but obviously you stand a chance of damaging your core. But im not certain this will cause your overheating problems?

You could bypass the heater with a short piece of copper tube and hose clamps. (or piece of hose as needed) Test to see if thats the problem/cure, without risking the heater core. **Be very careful with connections to heater core, may be fragile**. -Better to bypass away from the heater-.
-I'm leary of vinegar on all of the new parts. IF the test above points to the core , I suggest Reflushing JUST the core/hoses w/ diluted vinegar, let stand a few minutes then rinse and check what comes out and rate. repeat as needed

Good Luck

My opinion two problems, not related.

You have a plugged heater core--as recommended try a flush (or two, or three). I wouldn't use high pressure, not even medium pressure. Try pushing the water through one way, then switch and go the other way.

You probably have a weak fan clutch, idle or slow traffic jam speeds is when it is needed most. If you can handle the noise upgrade to NAPA 272310 HD ZJ fan clutch.

Way to go Joe !!! (fully agree)

In flushing the heater core is is better to connect the hose directly to the heater, not at the heater valve and fluch backwards dislodging what ever is stuck in there instead of pushing it further in.

Another note;... if you are flushing the control valve, make sure you turn the heater on to the very hot position. This opens the valve and allow the water to pass.

Having a blocked heater core wouldn't necessarily make you overheat. It would make you freeze in the winter.

Did you replace the water pump along with the t-stat? When my water pump was going out, it would overheat sitting still and at highway speeds.

Go ahead and replace your clutch fan too, it's probably on it's way out (or out already) if it's never been changed.

Don't install the HD fan, as you'll only be covering up your overheating symptoms.

Agree with Joe about likely fan clutch issues. On the road with good airflow, you are OK. When motor is hot, check for good resistance in fan clutch. It should rotate freely by hand when cold, and tighten up when hot.

Ive had this before on my first xj, and if your wondering what to turn freely means, spin a blade on the fan clutch as hard as you can by hand, on mine it spins about one complete full turn maybe a touch more but not much if at all. Then, to not turn freely! the blade that you spin will move like 1/4 of a turn.

Oh and regarding the flush of your core, i thought you had tried and failed already and were perhaps more kinda desperate than is maybe the case. But i have read many people go down the vinegar route when theve tried and failed with the alternating flush method. And is vinegar not less harsh on your core than the cleaning stuff that you can get. Ive never heard anyone say vinegar was too harsh, but i maybe wrong! Also ive seen others use a garage to hook up an air type hose joined with a water line type set up, and this blend of air and water gets pumped in. The mixture of air and water getting pumped in, is apparently effective without causing as much danger to your core bursting. Again these methods if repeated flushing fails. But i would keep patient with it because if you find yourself at your wits end, just look into heater core replacement!

The vinegar flush should work just as well in a heater core as it does in a drip coffee maker - which is good. We've saved buying another one again from our hard water in this area.

In a cooling system, it takes years longer to build up scale - but the same action happens. Vinegar breaks down the mineral deposits through chemical action and cleans the core internally, probably a lot better than a flush kit - leaving it in for 24 hours gives it the time it needs to work.

Which goes to show all those buying distilled water for their systems had a point, after all. The constant addition of mineralized water over years eventually coats the inside of the heater core - and the radiator!

In fact, the whole point of a spring in the lower hose is to prevent it getting sucked shut by the lack of flow through the core.

Could anyone be so kind as to confirm how a clutch fan should rotate by hand from a cold then hot engine. Ive confused myself. My existing xj (which does not overheat) from a totally cold engine, does not spin freely. The first two or three times i try to spin it, it stops dead. However if i try to spin it a further dozen times with the same cold engine, it frees up and eventually i can get it to rotate 5 or 6 times. But initially it stops pretty much as soon as my hand leaves the blade. With a hot engine, it spins easier on that very initial turn (maybe a full turn), but again it loosens up the more i try to spin it?

Doesn't an '89 have a coolant shut off valve to the heater core? Seems like that would mean that you don't need the flow for engine cooling. Way back when, if we were overheating in the summer, we would open the windows and run the heater to cool the motor down, but that was only for a FU system to start with. And I've bypassed leaking heater cores before with no issues. This is not the overheating problem. Is probably the fan.

dunbad said:

Could anyone be so kind as to confirm how a clutch fan should rotate by hand from a cold then hot engine. Ive confused myself. My existing xj (which does not overheat) from a totally cold engine, does not spin freely. The first two or three times i try to spin it, it stops dead. However if i try to spin it a further dozen times with the same cold engine, it frees up and eventually i can get it to rotate 5 or 6 times. But initially it stops pretty much as soon as my hand leaves the blade. With a hot engine, it spins easier on that very initial turn (maybe a full turn), but again it loosens up the more i try to spin it?

Click to expand...

Here's a link, but I'll have to personally test mine later.

http://www.naxja.org/forum/showthread.php?t=46429&highlight=fan+clutch

the mech fan should have a noticeable resistance when tried to turn freely on a hot engine. there is a viscus coupling inside that sences heat from the shaft of it to engage a clutch like mechanism. the hotter the engine, the stronger the fan should resist turning (when engine is running it would equate to stronger engagement= faster fan speed). when the engine is cool, it doesnt need as much air flow from the fan so it is allowed to free spin.

in regards to vinegar; i have used it with great sucess. my jeep was extremely neglected by its prior owners. when i got it, just about all the underhood rubber needed replacing, and the cooling system was junk. the t-stat was stuck open, heater core clogged severely, water pump on its way out. and the "coolant" looked like mud- color of mud not just muddy water, and noticeably thicker than coolant. initially i did numberous flushes to get a lot of crud out. it left a nice rust stain on the drive way from that. i waited on repacing components until i started to get a handle on the contaminate issue incase it dislodge a chunk that could granade parts. i noticed the worst part though. when i would squeeze either of the rad hoses or heater hoses it would CRUNCH from the mineral deposits inside.

i went though a half dozen water flushes until i could feel comfortable with a "cleaner" in the system. i ran the engine for about a week at a time with a solution of 1 gal of full strength coolant and 1 gal of distilled white vinegar. the first couple time freed up a lot of crud. the coolant was looking a lot better so i replaced the water pump, t stat and t stat housing. the old parts were still coated in crud but not as much as i expected. i went with the cheap parts incase replacement was needed after getting the crud out. i also replaced the hoses to now eliminate more crud.

i would frequently flush the cooling system out. i would do it when i would see the coolant change to a brown color. i would flush until the water came out clean and then refill with the 50/50 solution of vinegar and coolant. run it for a week. flush and re fill with 50/50 coolant distilled water (or pre mixed). repeat the cycle as needed.

once i had a handle on the coolant issue, i again replaced most of the cooling system- t stat+ housing, water pump, and hoses. for the most part all was well. although i learned later that the radiator still had a lot of crud in it. it sprang a leak so i went for a 3 core. no problem since.

it took me 2 years to get a handle on the crud in the coolant. now i have reverted to a yearly flush to keep everything proper. the vinegar helped to clean a lot of the junk out of there that a flush alone would not be able to clean out. just be sure to flush all the vinegar out and refill to make a proper 50/50 coolant water solution.

dunbad said:

Could anyone be so kind as to confirm how a clutch fan should rotate by hand from a cold then hot engine. Ive confused myself. My existing xj (which does not overheat) from a totally cold engine, does not spin freely. The first two or three times i try to spin it, it stops dead. However if i try to spin it a further dozen times with the same cold engine, it frees up and eventually i can get it to rotate 5 or 6 times. But initially it stops pretty much as soon as my hand leaves the blade. With a hot engine, it spins easier on that very initial turn (maybe a full turn), but again it loosens up the more i try to spin it?

Click to expand...

Everything anybody ever wanted to know about fan clutches:

http://www.haydenauto.com/products/fan-clutches-and-fan-blades.htm

awesome I will inspect and probably replace my fan clutch. thanks JOE!