kidkodiak

my 90' cherokee is having a heating problem I guess. The temperature gauge shows the truck sitting pretty consistently at about 230* when idling or slow driving, but drops back down to the average 210* when driving at normal speeds.

There are also wildly erratic swings in temperature on the gauge, sometimes pushing close up to the 250/260* range, then back down to about 220* very quickly.

I'm not sure what's up... I don't see any leaks in fluid, the fans seem to engage correctly, I've a new water pump installed a few months ago.

Any suggestions? I really want this thing to run cooler... it's the only issue on my old beater that I can't figure out , and other than this heating issue, it runs great.

Appreciate any help

solderjunkie

Don't assume the gauge is correct.

At 260 degrees, the coolant in the block would boil and you would have other symptoms... usually once you pass 260 it will peg the gauge because steam can't cool the engine.

Find somebody with an infrared thermometer to test the real temp of the thermostat housing.

Steelcityfan29

You have the same crappy pressurized system I had on mine. For about 150 bucks I swapped mine to the open system out of a 92 cherokee i found that had been rolled and the front end was perfect. I got the radiator had it pressure tested, it was great for a few other parts off the 92 and a few things from Napa.. out 150 bucks and my temp sits right about 200 no matter what now, its much better.

Steelcityfan29

I am NOT a mechanic at all. My friend who IS did this swap for me. This article was written by someone else.. I dont know where, it worked like a charm.

"
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 problems
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 gauge 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 gauge 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 you're 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' " "

I dont remember where I got it I just saved it on a word doc and used it. Thats basically what I did to my jeep but I got most of the parts off of a rolled totaled jeep from the local JY for next to nothing.

kidkodiak

I was wondering about the gauge. I know that it's running hotter than it should, but the erratic temperature swings on the dial made me wonder if something else was broken. I'll look into that suggestion, thanks


$150 bucks is my sort of repair Is any post'91 cherokee fair game for parts for this? I can go hit the JY and see what I can find, this might be a cool alternative (no pun intended)

Steelcityfan29

LOL I am not that mechanic of a guy.. my buddy did it for me and we used a totaled 92 and 93 for the better parts between the two. I think I had to get like 2 parts and some hose from napa.. and an overflow.. I used the universal overflow. you can see some pics on my post in jeep builds... called something like my 88 cherokee build <no name yet> . To see how it worked out.

a1racer

When you did your water pump did you do the thermostat to and did you flush the block when you had the chance I would also change the temp sensor and go to the open system if you can find on at the junk yard.

dwallace007

Here is a link for checking and verifying working temp sensors. You can quickly check the Temp sensor with a volt meter.

http://www.lunghd.com/Tech_Articles/...iagnostics.htm

Steelcityfan29

I flushed it and changed the thermostat too.. that was all cheap.. forgot to mention we purchased a new one too.

kidkodiak

Nope, was going to replace the thermostat on my next tune up... was going to do a pretty major tune-up here soon, once I have all of the stuff I need.

So...
1. new thermostat
2. new temp sensor
3. possible conversion to open system

anything else I could investigate or think about doing?

Thanks guys

Howler_GT

Change thermostat.
Flush system.
Both "good" things to do.

IF engine does not act wierd...change temp sending unit.
Do this "after" thermostat change if no difference in reading.

Does your rig have an open system?

Closed system usually has a huge "overflow" up against the firewall with tons of heater hoses running everywhere.

kidkodiak

I have the closed system with the Renix engine.

If I flush the engine AFTER I put in the thermostat, do I risk gunking it up? Should I flush it before and then install a new thermostat?

a1racer

Put the thermostat after doing the flush. And yeah going to the open system is not hard just get it from the junk yard then you should be set. And change your temp sensor so you are getting correct readings

Howler_GT

Whoops...my bad...

Typed in wrong order.

Flush then thermostat

fivendime

I'm having the same high temp fluctuations. It gets very hot when I go up hills and cools way down after I go down. Stays fairly consistent on the freeway and on back roads. Its just those hills that kill me. Plus the temp gauge sits past 210 all the time, and the motor is at that temp in about 4 miles of driving. I have replaced the radiator with a new 3 core, new heater control valve, water pump, t-stat, coolant temp sender, gauge temp sender and coolant all within 3000 miles and no change on the gauge? What the heck can be wrong here?

It also doesnt change much if I'm pulling a trailer, and the electric fan comes on with the AC but not when the motor gets hot.