I have a 6 cylinder 88 Cherokee that has 127,000 miles. I bought it used about 2 months ago and it run (ran) great. It appears the previous owners took decent care of it. It has now started running VERY hot! I have replaced the reservoir cap, thermostat, water pump, fan clutch and radiator within the last week and after all that the temp gauge will tach over in the red within 10 minutes idling in the driveway. I have no leaks, there is no milky or bubbly appearance on my dipstick and no smoke out of the exhaust pipes (the engine begins to smoke within that ten minute idle though). I have double checked to ensure the thermo. is installed properly and kept the reservoir cap of during the idle in an attempt to "burp" the system. One thing I did find odd was that even after the gauge hit red and I began to see smoke, The top rad. hose never got hot and I could not feel anything flowing, again the cap was off, so i don't know whether that lack of pressure caused this effect.
Between the valve cover and air filter there is a harness that holds some small lines. One of them is a vacuum that isn't attached to anything and when I place my finger over the hole it lowers my RPM. What is this supposed to be connected to and is it the cause of my over heat or have I blown a head gasket?

Not sure what the vacuum hose would be for but that top rad hose makes me have to ask if the the thermostat is in the right way. should be installed with the spring down.

otherwise you are experiencing a common problem for XJ's

JD

check out these web sites.

http://www.off-road.com/jeep/cherokee/98/06_jun/cooling/cooling1.html

http://www.off-road.com/jeep/cherokee/98/12_dec/radiator/radiator.html

http://jeepsunlimited.com/xj/cooling/cool.htm

They give some upgrades that will improve the cooling on these models.


JD

I've checked and then double checked the thermo (spring facing into block per the Haynes diagram). It's a Cherokee not a Cj, thanks though

it's likely air trapped in the system.

the hose that goes to the reservoir feeds from the water-pump, below the head and the upper radiator hose.

you can deal with it to some extent by parking on a steep hill, jacking or whatever it takes to get the rear end higher than the front (higher the better). then remove the sending unit for the temp gauge (back of the head), and burp out the air, then squeeze the upper radiator hose and push as much air as possible into the head so it can reach the opening. keep an eye on the reservoir and top it off as it empties.

this isn't a perfect fix but it will improve the problem.
another thing that helps are the 'water-wetter' products, just an additive that improves the heat transfer of coolant. it allows it to pick up heat from the engine faster and give it off in the radiator faster. when I was running it without a thermostat noticed about a 10 deg drop in temp.

drilling a small (1/8" or so) hole in the thermostat when installing a new one will help avoid trapping air behind it. it doesn't interfere with the operation of the thermostat and when burping the system you don't have to heat trapped air to a temp that will open it in order to allow coolant to protect your motor. on cars other than jeeps this will almost eliminate the need to burp the system after changing thermostats. on the Jeep of course you would still have to deal with the air trapped above the reservoir hose in the head, upper-radiator hose, and top of the radiator.

too bad you didn't look up some of the previous threads on cooling before you replaced all that you have. for about the same money you could have replaced it with an open-system conversion.

this is a very common problem on jeeps from the late 80's.

the cooling system is just poorly designed. so when you get cooling problems try and remember- Just Exchange Every Part.

Our driveway is on a bit of a slope (back of car lower than the front while idling) so this may have made my burping attempt worthless. I'm reluctant to do the "drill a hole in the thermo" suggestion so if I turn the car around so its facing down hill and ran it with the reservoir cap off will that work?

I have a '88 Laredo that had similar problems. Ran fine while moving but would overheat in a hurry at idle unless I ran the a/c to turn on the elec fan. I assumed that my fan switch was bad. When I replaced it, no coolant leaked out of the opening. Turns out I was only low on coolant. Sounds like you are too. Trapped air (As Capt talks about) will prevent you from topping off properly. I had a devil of a time doing it.

I ended up removing the top radiator hose and pouring in coolant there first. After reconnecting the hose I then topped of the bottle. I ran the engine at moderately high rpms and watched the coolant return in the bottle. As the level dropped, I added more coolant (just a little at a time). Let the engine cool completely and check/adjust the coolant level in the bottle.

After about 2 hours of this, I finally got the coolant level to remain fairly steady (some change will happen due to expansion). Now my fan kicks in when the engine gets hot like it's supposed to and I never see the temp get past about mid range on the temp gauge.

IMO, I agree that this is a poor design. However, at the moment, mine works fine so I'll leave it alone until something major breaks. Then I may swap it all out for an open system.

As far as your vacuum leak, which line is it on the block?

http://tinyurl.com/4q8zw will take you to a page with the vacuum hose diagrams. Follow every one until you find the one missing.

How much fluid shood I have lost when I took the bottom radiator hose off? Now that you mention it, I didn't get much. My electric fan works fine, it comes on for the A/C. I do not know that the overheating is isolated to only when it idles, because I won't drive it until I get this fixed for fear of baking the engine. Would the air bubble cause the engine to smoke?

When my 86 Cherokee Pioneer was found to be overheating I went through all of the checks and found that the space between the engine radiator and A/C radiator was clogged up with dirt and leaves. Might be worth checking. Also remove the cap and while engine is running check to see if the water is circulating past the spout. As the engine is revved up the water might even rise enough to overflow. If it does, real easy, the core is clogged or the thremostat is not opening. You might want to remove the thermostat during your troubleshooting process. That will eliminate that from the problem possibilities. If the water still will not circulate across the radiator the pump impeller is not doing its job.







I have a 6 cylinder 88 Cherokee that has 127,000 miles. I bought it used about 2 months ago and it run (ran) great. It appears the previous owners took decent care of it. It has now started running VERY hot! I have replaced the reservoir cap, thermostat, water pump, fan clutch and radiator within the last week and after all that the temp gauge will tach over in the red within 10 minutes idling in the driveway. I have no leaks, there is no milky or bubbly appearance on my dipstick and no smoke out of the exhaust pipes (the engine begins to smoke within that ten minute idle though). I have double checked to ensure the thermo. is installed properly and kept the reservoir cap of during the idle in an attempt to "burp" the system. One thing I did find odd was that even after the gauge hit red and I began to see smoke, The top rad. hose never got hot and I could not feel anything flowing, again the cap was off, so i don't know whether that lack of pressure caused this effect.
Between the valve cover and air filter there is a harness that holds some small lines. One of them is a vacuum that isn't attached to anything and when I place my finger over the hole it lowers my RPM. What is this supposed to be connected to and is it the cause of my over heat or have I blown a head gasket?

When I replaced the Radiator, I was able to get a clean look at the A/C rad. and there was nothing there to block it up. Here is where I show my ignorance...What is an "impeller" and what "core" is potentially clogged? I was told, by the person I bought it from, to only fill the reservoir to the midline (which is not quite to the top of the post) is this correct?

the impeller is the piece that moves the antifreeze in the water pump

the core is the part of the radiator that the antifreeze flows through to remove the heat.

JD

I thought so, but since I replaced the water pump and radiator and those parts are new, I thought you may have been refering to something else. What about the water line in the reservoir?

I'm not sure about the system you have.

Is the rad cap/filler neck on the radiator or on the reservoir???

If it is on the the reservoir, then you have the closed system and you need to bleed and bleed and bleed and bleed to get the air out..Capt apathy gave good instructions for this. Also, though it takes awhile, the complete heat/cool cycle will eventually fill the system and eliminate the air. Make sure that the reservoir is full when you shut off the hot engine and watch where the level moves to when it has cooled off completely. Some have suggested that 3 cycles will do it - but.........

Some times loosening a hose at a connection higher than the rad and working it slightly loose will let some air out of a high spot.

to fix this, think- air rises to the top- how can I release it.

Keep talking on here, maybe there will be other ideas come to some of us.


JD

Our driveway is on a bit of a slope (back of car lower than the front while idling) so this may have made my burping attempt worthless. I'm reluctant to do the "drill a hole in the thermo" suggestion so if I turn the car around so its facing down hill and ran it with the reservoir cap off will that work?

no, as it is the hose to the reservoir is at the water pump. running the engine with the car level may get some of the air out of the head (as it goes through the pump some of the air will go to the reservoir hose and burp some, but the majority will go through the upper radiator hose and just add to the massive bubble up their, which will take up almost all of the upper hose, and the top few inches of the radiator.)

to try and get that air out, you would have to get the thermos open and get a strong enough flow to push the huge air-bubble to the bottom of the rad, through the engine, over and over again many times. each time it goes through the pump a very small portion may pass to the reservoir hose (better odds if you have the heater on high to encourage some flow in that direction).

I've never seen a strong enough flow in my 89's system that would give me any faith in this happening.

the sensor for the temp gauge however is just a simple brass plug type (looks a little like a small, brass spark-plug), by removing this, parking the car with the rear-end high, and keeping the reservoir full you can get the air out of the head.

when coolant comes out, put the plug back in finger tight, and squeeze as much air as possible out of the upper rad hose, and back into the head. you have to almost completely squeeze the hose flat, and pushing the forward end low at the start will help encourage the air to go backward to the head, instead of into the radiator.

you'll have to repeat it quite a few times, until you get no air. then run the car until it's good and hot, and at high speed to work the air out, then park it and burp it again.

doing it without the hole in the thermostat will make it a bit harder. first of all the thermostat doesn't open until 190, everything is going to be very hot while you try to burp it.

having a hole that allows air to pass through the thermostat, simplifies the process and allows you to do it easily while cold.

drilling the hole is completely safe. I've been doing it to every car I've owned since the early 80's. it doesn't interfere with the thermostat or effect the operating temp at all, since it opens and closes to maintain a certain temp it just opens slightly less (since the hole is letting some by) before the coolant cools enough to stop it from opening further.

also it seems to help in the event of failed thermostats (if you have the kind that fail closed), if your thermostat fails in the shut position, your car will over-heat, without any circulation the coolant temp could shoot up and (depending on your % of water) trap a steam bubble behind the thermostat. the small hole, doesn't let any serious amount of water through but air and steam quickly pass through and makes sure your engine is fully protected by coolant.

also when you first install it and you have an air bubble behind the thermostat you have to get your car a lot hotter to get it to open, than you would have with water at the same temp.

I've even noticed the latest thermo I installed in my wifes Volvo already had a hole in it. I guess the suppliers are catching on.

after research and checking with some pro mechanics, it's air in the system, some of the suggestions here worked for me, especially having the vehicle tilt with the rear up front down, and removing the temp sender from the left rear of the head and letting the block fill, it is a poor design, i am still purging after several hot and cold cycles, but my temp seems to be steady, and both top and bottom hose are now heating equally, one other hint, one of the suggestions i found in here, drill small whole in the thermostat, instead i can suggest an alternate part no to the regular catalogues, it is also side stepped so that you won't accidentally break the housing when reinstallin it, let me know if you need the part no., duke.

Whats that part for the thermostat fix Dmagg.

hi viper, for 180 degrees, use stant part 13858, for 195 degrees, use part 13859, these stats are offset, if not real carefull bolting up the regular listed thermostat it is possible to crack the old housings, and they come with a poppet valve, early parts catalogues showed these numbers for jeep 4.0 litres, then they replaced with conventional looking stats, we had complaints of snapping cast housings so we send the old listed part numbers they seem to eliminate lots of headaches, good luck, by the way a 1/2" long crack in the seam of my pressure bottle was my culprit for engine coolant boiling, again good luck on a terribly designed system, dmagg.

It's fixed. I've replaced so many parts (prior to involving this forum) and lastly got most of the air out of the system. I'm not sure which part that was replaced fixed it, but I sure wish I talked with everyone here before I spent any money. Thanks for all your help.

Last question (for now); what is the correct oil pressure reading?

Last question (for now); what is the correct oil pressure reading?

Normal oil pressure should be 13 psi at 600 RPM or 37-75 psi at 1600 RPM.

Pardon my ignorance, but my guage (on the dash) reads from I think 170ish to 220ish, what should it read in there at an idle?

Pardon my ignorance, but my guage (on the dash) reads from I think 170ish to 220ish, what should it read in there at an idle?

that'd be your temp guage. it should be reading around 195-205 when warmed up.

For all of you that have a pre 1992 Jeep Cherokee with 4.0 Ltr 6cyl engine. I have the solution to your cooling system wows. My Jeep Cherokee is a 1988.
The stock Pre 92 system is a closed system with no radiator cap and complicated plumbing for the heater core and the coolant expansion tank.
The problem with the system, as I'm sure your already aware.
1. The coolant expands and blows out of the expansion tank cap with no place for it to recover from.

2. The electric coolant fan switch is in a bad location and rarely turns on the fan when needed because of constant coolant loss leaving the sender un-exposed to coolant, and its location in the radiator is a cold spot because of the design of the radiator.

Remove the original radiator and replace it with a Modine NAPA # 2802 or equivalent. This radiator is listed for a 1992 Jeep Cherokee. This radiator is an open system exact fit and has a radiator cap/fill neck. All hoses and transmission lines will connect in the same place. This radiator does not have a provision for the fan switch (I will get to this).
The proper radiator cap for this unit is NAPA #705-1445

Remove the water outlet (thermostat housing) and replace it with the housing from a 1993 4.0 6 cyl Cherokee. This is a dealer or auto recyceler item. This housing is an exact fit with all of the hose positions in the same place. In addition this housing has a hole tapped into it for the 1993 temp gage sending unit. This is were you will mount a Fan switch to replace the one that was on the origional radiator. This new switch location has better heat transfer to the switch so the electric fan will cycle more frequently thus resluting in better cooling.
Since you have the housing off this is a good time to replace the thermostat.

You will need a Fan switch. I used NAPA # FS113, and the proper connecter to this switch is NAPA # FSC10. This will turn on the fan between 207-220 degrees. The origional radiator mounted switch activated at 230 degrees. As mentioned earlyer the new fan switch mounts in the 1993 thermostat housing.
The switch is a single pole switch with one wire and switches to ground so you will have to use a head light/horn relay to connect it to your original fan wires.

1. Run the new fan switch wire to the ground terminal of the relay.

2. Carfully cut off the original wires with plug from the original radiator mounted fan switch. Cut them off at the switch side so you have the plug with the wires attached. The yellow wire is +12V and the black wire goes to the original fan relay. Connect the wires with plug to the switched (load = yellow, output= black) terminals of the relay. Since the yellow wire is hot +12v when the ignition is on use this wire (make a jumper to connect to the + side of the relay) to power (activate) the relay.

Recap step 2. Yellow wire goes to relay + (positive) and relay load terminals. Black wire goes to relay output terminal. Fan switch goes to relay - (minus /ground) terminal.

3. Remove all heater hoses, coolant expansion tank and mount, metal y-pipes, and heater valve if your model has one. Be carfull not to break the plastic vacume line attached to the heater valve as it can become brittle.

4. Install heater valve NAPA #660-1174. This valve has 4 connections. Looking at the valve from the opposite side from the vacume switch with the curved end of the valve facing upward you will see one connection facing forward, two connections facing back and one facing at a 45 degree angle facing towards you. On the bottom angled connection run a 5/8" heater hose to the thermostat housing. On the single connection on the front run 5/8" heater hose to the water pump. Connect the two rear facing connections to the top and bottom connections of the heater core. Connect the vacume line that was connected to your old valve to the connection on the new one.

5. Purchase an after market coolant recovery tank and mount it in the hole were the old coolant expansion tank/mount was removed from.

6. Run a 5/16 fuel line or equivalant from the expansion tank to the fitting just below the radiator cap.

7. Fill cooling system using standard methods and precautions.
Parts list. I used NAPA auto parts as a source so all part numbers are NAPA numbers. These are standard replacement parts and can be purchased from any after market or dealer source.

1. Modine Radiator # 2802 for 1992 Jeep Cherokee.

2. Radiator cap #705-1445.

3. Coolant Fan Switch # FS113.

4. Fan Temp Switch Connector # FSC10.

5. Heater Valve # 660-1174

6. Water outlet from 1993 Jeep Cherokee (dealer only or auto recycler).

7. Standard 30amp Headlight/Horn Relay.

8. 8' 5/8" Heater Hose.

9. 10' 5/16 Fuel line.

10. Teflon tape or equivalant thread sealant for Fan switch threads.

11. Small roll of 12 gage wire.

12. Small package of 1/4" spade connecters to connect wires to relay terminals.

13. Small package of butt connectors to connect fan switch to wire going to relay.

14. Two gallons of Antifreeze/Coolant.

You will now have a standard open cooling system like every other car on the road. No more will you be stuck on the side of the road with an over-heated Jeep as the result of running out of coolant because of the Renult designed closed cooling system. When you add coolant to the new system you will know that your radiator is full because you fill the radiator now, and you now have an overflow tank that will return the expanded coolant into the radiator when it cools down (just like every other car on the road.

This conversion takes about three or four hours depending on your abilitys. Show this list to any radiator shop and they will know what to do if your not a do-it-yourselfer.

The bottom line....This conversion will cost you about $350 to $400, about the same as replacing the origional components, but with the benifit of no more problems and the insurance of not overheating and causing expensive engine damage.
Happy Jeepin'