When I first bought my Cherokee the temp needle reached the middle just fine. Now for some reason it started only going up 1/4 of the way and no matter how hard I drive the car never warms up to full operating temperature. Any idea why this might be?

Also, kind of odd but ever since I first bought my Cherokee the fan turns on all the time. It will go on for 15 seconds, then go off, then go back on for 15 seconds, then go off. It's not running hot or anything, the fan just clicks on and off all the time.

 

Sticking thermostat?

Bad temp sender?

 

Verify temps at warm up with a temp gun. Could be the thermostat stuck open. If that's the electric fan your talking about then that's normal. It will come on when the a/c compressor kicks on. So depending on the weather and what your heat or a/c is set at it will kick on and off with the compressor.

 

Efan rapid on/off sounds like low refrigerant.

Does the heater work good when the gauge displays 1/4? If yes, probably faulty gauge reading....if no, probably stuck open t-stat.

 

XJ's have a fan clutch, right? If It's slipping it could be only working part way...
Edit.. Not unless it's electric.. Like OP's.. NM..

 

I had the same problem it mine was a problematic thermostat

 

Let's see...

I know that my refrigerant is low because the previous owner completely drained the AC when he was working on the motor and had to remove an AC line. Does low refrigerant really cause the fan to go on that much? If so, why?

And yes, my heat works just fine, the car doesn't overheat at all, it runs perfectly. I don't own a temp gun but I'll see how much they cost.

Parts are so cheap it might be cheaper just to buy a new thermostat and temperature sensor.

 

Agreed. New thermostat and temp sensor would be good. Never a bad thing to replace parts. I'd go with mopar. Your ac will kick on and off with low Freon.that's why the fan keeps coming on and off. There's got to be a little to no Freon left in the system. Mine was doing somewhat the same thing. I then evac and recharged it only to find out once the compressor started to actually work it hit the bucket. But o well. All good now. New compressor and now ice cold ac. I would have yours checked out. Probably do an evac and recharge. Make sure its working properly.

 

Before you start throwing money at parts:
the temp gauge issue you see, is likely the sending unit, and has nothing to do with your engine not getting warm enough. Your heater is fine, suggesting normal warmed up coolant/engine temp. Its not overheating either, so fan and thermostat are doing what they should.
A stuck open thermostat gives you a slower rising engine temp after cold start, but since the 4.0 6 cyl produces quite some heat, it will usually not result in an too cool engine. Overheating is the issue in these engines most of the time.

The temp sensor or sending unit therefore is likely up for replacement.
If you decide to replace your thermostat, replace it with a 195 F one (for you guys in the US) and consider other parts of the coolant system as well, if thats not been done. this way you only have to drain en refill system once.

Regarding the kick in/off of the fan: this is normal operation and happens when your engine operating temp is fluctuating between the preset limits: high side>fan kicks in till cooled enough and switches off. And yes, this happens even in these short cycles.
(Your ac system works somewhat different related to pressures and has low and high pressure switches to regulate this. Other issue.)
See how you go with replacing temp sending unit/sensor.

 

Hey guys, need some help here. Bought my 98 jeep cherokee xj about two years ago. First car I've gotten to fix solo with no help so still learning. Started to have a coolant leak on my floorboard so I of course took on the HORRIBLE task and replaced the heater and ac component inside...had the hoses replaced and new coolant pressurized through. Went ahead and replaced the squirrel cage and the little heat thing that glows red under the glove box...(cant think of the name of it atm) but thought she would be ready for winter right?...wrong :/ heat sloooowly started to get cooler and cooler so I said hey..must be the thermostat...got a "fail safe" one that's set at 165° and replaced the whole thermostat housing etc bcuz it was only $11...still no damn heat!!! Shes got no leaks anywhere and both hoses are hot. Only thing I can think of left that I haven't replaced is the water pump??? Any help would be awesome! Thanks.

 

165 is far too cold for a Cherokee. The original thermostat it set to 190 and that is what should be used.

 

195* thermostat and if you still have a heater control valve in the hoses, get rid if it. Run the heater full flow. Most people don't realize the A/C runs in defrost. The fan comes on with the compressor and when the compressor senses no pressure, it cycles off. If you don't want the fan to run, pull the connector on the compressor clutch. The fan will still come on if the temp goes over 210*

 

Cruiser highly recommends Mopar thermostats - and considering he's a former head Jeep mechanic, he knows what he's talking about.

98 won't have a Heater Control Valve, so it's already been eliminated.

If it were me - I'd start by getting a Mopar T-stat and when you go to put it in, take a garden hose and flush out the new heater core forward and backward (just to be sure).

Edit -- If you're going to put in a water pump - I'd do the t-stat, pump and flush at the same time. I'm of the mind that if you even question the water pump - replace it. Breaking down 500 miles from home will do that to you. So I won't ever dissuade someone from replacing their water pump - despite in your case feeling like it's virtually certain that it isn't causing your heating woes.

Make sure the system is burped (look this up if you're unfamiliar - lots of threads describe the procedure)

At that point, if you're still not getting heat, I'd see if the blend door is stuck. Another possibility (dave can elaborate ) is that the seals on the air ducts are leaking cold air that is killing the efficiency of the system.