Cooling Problems

I am having problems with my 1991 Jeep Cherokee (222,000+ miles). The temperature light starting coming on a few weeks ago. I had previously put Bars stop leak in my radiator to stop a small leak.
Since then, I have replaced the thermostat twice, flushed the radiator and engine coolant system, replaced the coolant temperature sensor, and yesterday replaced the radiator with a GDI 3-row. Also, my mechanic had inspected it and said the head gasket, etc looks fine. The light is still coming on. The water pump was taken off and inspected and looks fine since it is less than 2 years old.

I don't feel coolant flowing through the upper radiator hose after the light comes on, so I think it is a flow problem. Also, after the temp light comes on the radiator is hot, but the radiator cap is not hot. I am not sure if there is a clog somewhere in the engine, the water pump is busted or something else.

Someone please offer suggestions. Thanks.

I had previously put Bars stop leak in my radiator to stop a small leak. one word-DON'T

they guy who had mine before me used that crap and it took forever to get it out.

I end up removing the thermostat and putting in the prestone super-clean (you leave it in for 5 hours of full temp driving time). I used that 3 times. and would back flush it every day in between (unhook the upper radiator hose, with thermostat out, and jam the garden hose into the hose the water flowed backward through the radiator. I'd also use a small (5/16 dia) hose to siphon from the bottom of the radiator as the water was flowing out ( I'd get a couple tablespoons worth of debris each day). finally after several weeks of this I got it clean enough that I was no longer getting that nasty black bars-leak residue after using the cleaner and put the thermostat back in and every things been fine. except that after all the worry about the overheat I used a 180 thermostat and now I have trouble getting it warm enough on the cool days.

you also need to get the air out of that upper hose to get good circulation. the only way I've found to do this (I wish I could remember who to credit with telling me this) is to park the jeep facing downhill on the steepest hill you can find (or jack up the back). squeeze the hose and work the air pocket back into the head. then remove the temp gauge sending unit and let the air-bubble out. I then started it ran it for a bit on fairly high revs, then shut it down and tried for the air-bubble again. that got most of the air out, you can definitely feel the water through the hose now.

Thanks for the advice, I will try it tonight. Now I know about not using Bar's.....and my radiator is brand new and I put in a 180 thermostat as well. Hopefully your fix to get the air pocket out will do the trick.

What about the heater box or is there another drain for the cooling system on the motor to see if there is a clog there? It seems like it is some type of clog in the cooling system or the water pump is not functioning properly. Any other suggestions in case the "air pocket" fix doesn't work?

when you run the water back through the system, take the cap off the pressure bottle, put your garden-hose running in your radiator hose, and the water should run out the top of your radiator. if the water doesn't flow easyily from your radiator and is flowing back out the bottle instead (the bottle is higher), then I'd guess you have a clog.

the thing about that bars leak is that you put this whole can of crap in the cooling system, it likely only uses a little bit to close the hole, meanwhile this stuff is running through your system and the radiator is colder than the engine (especially right after the thermostat opens, and the stuff can start flowing). if you think it through, that leaves fairly good odds that the bars-leak will cool and jell back up in your radiator, once it jells and blocks part of the radiator there is no water(coolant) circulating in that part to melt it again. in effect it just glues part of your radiator core shut(thats how it patches the hole). thats why it took several times using the long-term cleaner(and letting the engine get hot for long periods) to finally get all that crap out of mine.

I'm far from being an expert machanic (I mainly only learn how to do a repair when I can't afford to pay someone else), but I don't usually trust a fix that comes in a can.

This is probably too late, but what's lost? The Cherokee you speak of I assume has a 4.0 Liter L6. If this is the case, and I am sure it is, then you may be experiencing a air lock in the coolant system. This engine notorious for this problem. If the coolant ever leaks to a certain point, or is drained, then you have to purge the air out of the system. The best way that I have found is to remove the thermostat and the radiator cap. Reattach the thermostat housing without the thermostat installed and reattach the upper radiator hose. Detach the upper hose at the radiator side and hold it as high as you can. Start adding the coolant in the hose not letting it down ( a helper is nice due to the awkwardness). Fill the hose until the coolant starts to flow out of the radiator cap, whether it is on the overlow jug or on the radiator itself. Another method I have been told works, but I have never tried, is to remove the coolant temperature sensor from the rear of the cylinder head and add coolant to the radiator cap neck or overflow bottle until coolant starts to flow out of the cts hole. Reinstall the CTS and Wah Lah. Oh, another suggestion is that the impeller may have been corrored, broken or spinning on the water pump. If this is the case, I highly suggest flushing the cooling system due to a possible electrolyis problem. Additives are available to neutralize the contaminents that cause this, but a good old fashion flushing is highly recommended.

Thanks for your reply. I think I have it solved.......the problem is that it has been so cold outside here that I am not sure if the overheating problem is actually solved, or the outside temp is keeping the engine cool enough. I guess I will find out soon as it has been getting in the 70's here.

I have tried a similar method you suggested as well as changing the radiator, thermostat, radiator cap, water pump, temp sensor, as well as flushed the entire system including the heat pump and all hoses (multiple times). I seem to be getting pressure now, so hopefully the problem is solved, just not sure if there is enough flow or not.......but the upper hose seems pressurized when the engine is running.....

If you can think of anything else, please feel free and reply, just in case the light decides to pop on again once temperatures start getting in the 80's and above.

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'

BCBlues, thanks for your reply.

My 1991 Cherokee is an open cooling system, it has a radiator cap, overflow tank, etc. I think the pre-1989 models are closed systems.

BCBlues, thanks for your reply.

My 1991 Cherokee is an open cooling system, it has a radiator cap, overflow tank, etc. I think the pre-1989 models are closed systems.


Your welcome,

My jeep is an 1988 Laredo (fully loaded and clean, stock with no lift -family car) with 230,000 Miles and it was constantly over heating and blowing out its coolant and getting air lock. It has a new out of the crate re-manufactured engine and transmission (now with 10,000 miles on it), all new sensors, starter, starter realy, and lots of other new parts, and I had put in a new stock radiator, fan sensor, expansion tank, and cap. After all of that it still over-heated in traffic, and on grades.

I combed the wrecking yards and looked at all the differances in the year models. I then came up with this conversion.

The funny thing is I have since found other articles from other Jeep owners that have basicly done the same thing.

For those intrested I have about 5000 miles on the conversion. Have driven with full passanger, luggage, and towing a small boat and have not lost any coolant or had any over-heating problems after doing this conversion. The temp gauge never moves, and stays just under the center mark.

My AC doesnt work at this time so we will see how that effects the engine temp when I get around to fixing that.

I also changed the thermostat (190 degree), water pump, fan clutch, and all hoses at the same time and did a full system flush.

I used all new components, not re-manufactured anything.

So far so good!!!