Cooling system problems

Hey all,

I'm having problems with the cooling system on my '89 cherokee.

The first (and in my opinion most serious) is that my temperature gauge never gets above 190* or so (half way between 2nd and 3rd lines on the gauge). The gauge has 5 lines with the 1st labeled 100*, the 3rd labeled 210* and the 5th labeled 260*, so I'm guessing on the exact value. I replaced the thermostat 7 months ago assuming that it was the problem, but no change. When I start it, the gauge goes to full scale, but no matter how far I drive, it never rises above the mentioned point.

The second problem is that the electric fan runs all the time--A/C off immediately after starting (even before starting in the run position). Based on other threads here, this is not normal. I've replaced the relay for it and nothing changed, so I'm a little stumped on where to look next. This may help explain the first problem, but I'm not sure.

A little background on the jeep: 89' Cherokee, 4.0L, 236k miles, original engine, 4WD, towing package.

Chris

Unplug the eletric fan or take the relay out and see where the temp runs. The fan only is supposed to turn on at 210 which is slightly over the halfway mark on your temp gage. Next find a service manual, there is a very detailed description of how to check the fan for correct operation.

I have the Haynes manual for it, is that sufficient? Alternatively, I also have the Mitchell On-Demand System v1.50.003, but it's a little hard to follow.

The Mitchells is proably from the service manual. One other option that is quite common is to wire a switch into the circuit so you can turn the eletric fan on when you want. Do a search to find out how.

I have a 88 XJ and here is what I have learned about the temperature gauge and electric fan. The electric fan is to come on when :

1) The temperature in the cold tank of the radiator is 190F. The sensor in the tank is a switch which closes the fan relay.
2) The AC compressor engages and the fan will turn on, when the AC compressor disengages the fan turns off. If you are running defrost the AC compressor will also cycle.

You could have a bad fan relay. It is located on the driver's fender between the wash bottle and the air filter box but you said you changed it. I'd next disconnect the switch in the radiator. You will find the connector near the air front opening of the air box. With it disconnected start your XJ and see if the fan still does the same thing. If it stops then replace the fan switch in the radiator, figure on $20 for that part.

As someone else said you could remove the relay. I'd do this after you disconnected the radiator switch. Hopefully the fan will not run with the relay missing. If the fan continues to run with the relay missing then you have a major wiring problem and will need an electrician to fix it.

When the AC system engages the electric fan it is done using the AC relay. You may also want to look at that relay and replace it for age if nothing else. The AC relay turns on and it turns on the fan relay. So it the radiator switch and fan relay OR AC relay turning on the fan relay.

It can be fixed...

Thanks all, it was simply the switch in the radiator--unplugged it and the fan quit running--plugged it back in and away it went again. It appears that my engine temperature sensor is fine and the permanently running fan was keeping the engine too cool.

I would change out the temp sensor switch in the radiator if I was you but this begs the next question "how old is the radiator?" If it is the factory radiator it could be at the end of it life cycle. That is why the fan runs all the time.

Having the fan run all the time is not a good thing, it can mask a real cooling system problem. At road speeds you don't need fans due to the air being forced through the radiator.

I replaced my 88 XJ radiator in Feb this year. I had a 4 year old GDI which had a small leak at the end tank/core crimp. I went with a new Modine and it has not leaked. With an older vehicle replacing radiators is just part of the experience.

I am worried you may also have a damaged thermostat that opens early. I'd install a new mopar thermostat while I was changing the radiator.

I strongly recommend you change the switch in your radiator and see if the fan cycles. Then monitor the engine temperature and decide if the radiator needs replacement.